Compilation Process
src code -> executable
What is a Compiler?
A compiler translate's source code into an machine readable executable.
C Compilers
GCC
GCC stands for GNU Compiler Collection.
Clang
clang llvm backend for compiling C, C++, Objective-C, and Objective-C++.
C Program Compilation Pipeline
Take src code and produce a binary(executable) with a pipline (steps).
C program compilation rule
- Only source files are compiled
- Each source file is sompiled separately
Pipeline steps:
- Preprocessor from .c to .i (preprocessed src)
- ↓
- Compilation from .i to .s (asm src)
- ↓
- Assembly from .s to .o (machine code obj file)
- ↓
- Linker link the generated object files
- ↓
- executable
Output of one component becomes the input of the next component. The generated binary depends on the OS/ARCH.
To get all intermediate files run:
-Wall enable most error warnings -save-temps do not delete intermediate files
gcc –Wall –save-temps main.c
ls
a.out main.bc main.c main.i main.o main.s
All intermediate files:
- main.i – Product by Preprocessor step
- main.s – Product by Compiler
- main.o – Product by Assembler
- a.out(Linux) – executable
Step 1 – Preprocessing
Writing a C program:
- include libs
- define macros
- conditional compilation.
All of these are considered to as preprocessor directives.
Header Files
The source file consists of a number of header files in the C language, and it is the preprocessor’s task to include the library.
Example:
If the program contains #include, this line will be replaced by the original contents of the header file when the source file is pre-processed. Macros
Macros are defined by #define syntax in the C programming language. During the preprocessing stage, the macros are replaced by their values. Conditional Compilation
Often we want our compiled code to be minimal, so we can use conditional compilation. The preprocessor often operates on a conditional compilation and reduces the code by adding only those lines that fulfill the condition.
Some Conditional Compilation preprocessor directives are:
- #undef
- #ifdef
- #ifndef
- #if
- #else
- #elif
- #endif
Comments
For improved readability and more reference to the code, we use the comments in our code. However, the comments do not provide the computer with the necessary information and therefore the comments are removed in the pre-processing stage.
The pre-processed code is often called the Translation Unit (Compilation Unit).
You can see the pre-processed code of the C program in the section below.
Extract preprocessed code from GCC
We can also take a look at the file from each part of the compilation pipeline. Let’s ask the C compiler driver to dump the translation unit without going any further.
To extract the translation unit from the source code, we can use the -E option in the GCC.
generate preprocessed file
gcc -E main.c -o main.i
c src
#include <stdio.h>
#include <stdlib.h>
// MAX comment will be removed
#define MAX 10
int main() {
printf("Hello world\n");
printf("%d\n", MAX);
return EXIT_SUCCESS;
}
preprocessed example
preprocessed
# 0 "main.c"
# 0 "<built-in>"
# 0 "<command-line>"
# 1 "/usr/include/stdc-predef.h" 1 3 4
# 0 "<command-line>" 2
# 1 "main.c"
# 1 "/usr/include/stdio.h" 1 3 4
# 27 "/usr/include/stdio.h" 3 4
# 1 "/usr/include/bits/libc-header-start.h" 1 3 4
# 33 "/usr/include/bits/libc-header-start.h" 3 4
# 1 "/usr/include/features.h" 1 3 4
# 392 "/usr/include/features.h" 3 4
# 1 "/usr/include/features-time64.h" 1 3 4
# 20 "/usr/include/features-time64.h" 3 4
# 1 "/usr/include/bits/wordsize.h" 1 3 4
# 21 "/usr/include/features-time64.h" 2 3 4
# 1 "/usr/include/bits/timesize.h" 1 3 4
# 19 "/usr/include/bits/timesize.h" 3 4
# 1 "/usr/include/bits/wordsize.h" 1 3 4
# 20 "/usr/include/bits/timesize.h" 2 3 4
# 22 "/usr/include/features-time64.h" 2 3 4
# 393 "/usr/include/features.h" 2 3 4
# 490 "/usr/include/features.h" 3 4
# 1 "/usr/include/sys/cdefs.h" 1 3 4
# 559 "/usr/include/sys/cdefs.h" 3 4
# 1 "/usr/include/bits/wordsize.h" 1 3 4
# 560 "/usr/include/sys/cdefs.h" 2 3 4
# 1 "/usr/include/bits/long-double.h" 1 3 4
# 561 "/usr/include/sys/cdefs.h" 2 3 4
# 491 "/usr/include/features.h" 2 3 4
# 514 "/usr/include/features.h" 3 4
# 1 "/usr/include/gnu/stubs.h" 1 3 4
# 10 "/usr/include/gnu/stubs.h" 3 4
# 1 "/usr/include/gnu/stubs-64.h" 1 3 4
# 11 "/usr/include/gnu/stubs.h" 2 3 4
# 515 "/usr/include/features.h" 2 3 4
# 34 "/usr/include/bits/libc-header-start.h" 2 3 4
# 28 "/usr/include/stdio.h" 2 3 4
# 1 "/usr/lib/gcc/x86_64-pc-linux-gnu/12.1.0/include/stddef.h" 1 3 4
# 214 "/usr/lib/gcc/x86_64-pc-linux-gnu/12.1.0/include/stddef.h" 3 4
# 214 "/usr/lib/gcc/x86_64-pc-linux-gnu/12.1.0/include/stddef.h" 3 4
typedef long unsigned int size_t;
# 34 "/usr/include/stdio.h" 2 3 4
# 1 "/usr/lib/gcc/x86_64-pc-linux-gnu/12.1.0/include/stdarg.h" 1 3 4
# 40 "/usr/lib/gcc/x86_64-pc-linux-gnu/12.1.0/include/stdarg.h" 3 4
typedef __builtin_va_list __gnuc_va_list;
# 37 "/usr/include/stdio.h" 2 3 4
# 1 "/usr/include/bits/types.h" 1 3 4
# 27 "/usr/include/bits/types.h" 3 4
# 1 "/usr/include/bits/wordsize.h" 1 3 4
# 28 "/usr/include/bits/types.h" 2 3 4
# 1 "/usr/include/bits/timesize.h" 1 3 4
# 19 "/usr/include/bits/timesize.h" 3 4
# 1 "/usr/include/bits/wordsize.h" 1 3 4
# 20 "/usr/include/bits/timesize.h" 2 3 4
# 29 "/usr/include/bits/types.h" 2 3 4
typedef unsigned char __u_char;
typedef unsigned short int __u_short;
typedef unsigned int __u_int;
typedef unsigned long int __u_long;
typedef signed char __int8_t;
typedef unsigned char __uint8_t;
typedef signed short int __int16_t;
typedef unsigned short int __uint16_t;
typedef signed int __int32_t;
typedef unsigned int __uint32_t;
typedef signed long int __int64_t;
typedef unsigned long int __uint64_t;
typedef __int8_t __int_least8_t;
typedef __uint8_t __uint_least8_t;
typedef __int16_t __int_least16_t;
typedef __uint16_t __uint_least16_t;
typedef __int32_t __int_least32_t;
typedef __uint32_t __uint_least32_t;
typedef __int64_t __int_least64_t;
typedef __uint64_t __uint_least64_t;
typedef long int __quad_t;
typedef unsigned long int __u_quad_t;
typedef long int __intmax_t;
typedef unsigned long int __uintmax_t;
# 141 "/usr/include/bits/types.h" 3 4
# 1 "/usr/include/bits/typesizes.h" 1 3 4
# 142 "/usr/include/bits/types.h" 2 3 4
# 1 "/usr/include/bits/time64.h" 1 3 4
# 143 "/usr/include/bits/types.h" 2 3 4
typedef unsigned long int __dev_t;
typedef unsigned int __uid_t;
typedef unsigned int __gid_t;
typedef unsigned long int __ino_t;
typedef unsigned long int __ino64_t;
typedef unsigned int __mode_t;
typedef unsigned long int __nlink_t;
typedef long int __off_t;
typedef long int __off64_t;
typedef int __pid_t;
typedef struct { int __val[2]; } __fsid_t;
typedef long int __clock_t;
typedef unsigned long int __rlim_t;
typedef unsigned long int __rlim64_t;
typedef unsigned int __id_t;
typedef long int __time_t;
typedef unsigned int __useconds_t;
typedef long int __suseconds_t;
typedef long int __suseconds64_t;
typedef int __daddr_t;
typedef int __key_t;
typedef int __clockid_t;
typedef void * __timer_t;
typedef long int __blksize_t;
typedef long int __blkcnt_t;
typedef long int __blkcnt64_t;
typedef unsigned long int __fsblkcnt_t;
typedef unsigned long int __fsblkcnt64_t;
typedef unsigned long int __fsfilcnt_t;
typedef unsigned long int __fsfilcnt64_t;
typedef long int __fsword_t;
typedef long int __ssize_t;
typedef long int __syscall_slong_t;
typedef unsigned long int __syscall_ulong_t;
typedef __off64_t __loff_t;
typedef char *__caddr_t;
typedef long int __intptr_t;
typedef unsigned int __socklen_t;
typedef int __sig_atomic_t;
# 39 "/usr/include/stdio.h" 2 3 4
# 1 "/usr/include/bits/types/__fpos_t.h" 1 3 4
# 1 "/usr/include/bits/types/__mbstate_t.h" 1 3 4
# 13 "/usr/include/bits/types/__mbstate_t.h" 3 4
typedef struct
{
int __count;
union
{
unsigned int __wch;
char __wchb[4];
} __value;
} __mbstate_t;
# 6 "/usr/include/bits/types/__fpos_t.h" 2 3 4
typedef struct _G_fpos_t
{
__off_t __pos;
__mbstate_t __state;
} __fpos_t;
# 40 "/usr/include/stdio.h" 2 3 4
# 1 "/usr/include/bits/types/__fpos64_t.h" 1 3 4
# 10 "/usr/include/bits/types/__fpos64_t.h" 3 4
typedef struct _G_fpos64_t
{
__off64_t __pos;
__mbstate_t __state;
} __fpos64_t;
# 41 "/usr/include/stdio.h" 2 3 4
# 1 "/usr/include/bits/types/__FILE.h" 1 3 4
struct _IO_FILE;
typedef struct _IO_FILE __FILE;
# 42 "/usr/include/stdio.h" 2 3 4
# 1 "/usr/include/bits/types/FILE.h" 1 3 4
struct _IO_FILE;
typedef struct _IO_FILE FILE;
# 43 "/usr/include/stdio.h" 2 3 4
# 1 "/usr/include/bits/types/struct_FILE.h" 1 3 4
# 35 "/usr/include/bits/types/struct_FILE.h" 3 4
struct _IO_FILE;
struct _IO_marker;
struct _IO_codecvt;
struct _IO_wide_data;
typedef void _IO_lock_t;
struct _IO_FILE
{
int _flags;
char *_IO_read_ptr;
char *_IO_read_end;
char *_IO_read_base;
char *_IO_write_base;
char *_IO_write_ptr;
char *_IO_write_end;
char *_IO_buf_base;
char *_IO_buf_end;
char *_IO_save_base;
char *_IO_backup_base;
char *_IO_save_end;
struct _IO_marker *_markers;
struct _IO_FILE *_chain;
int _fileno;
int _flags2;
__off_t _old_offset;
unsigned short _cur_column;
signed char _vtable_offset;
char _shortbuf[1];
_IO_lock_t *_lock;
__off64_t _offset;
struct _IO_codecvt *_codecvt;
struct _IO_wide_data *_wide_data;
struct _IO_FILE *_freeres_list;
void *_freeres_buf;
size_t __pad5;
int _mode;
char _unused2[15 * sizeof (int) - 4 * sizeof (void *) - sizeof (size_t)];
};
# 44 "/usr/include/stdio.h" 2 3 4
# 52 "/usr/include/stdio.h" 3 4
typedef __gnuc_va_list va_list;
# 63 "/usr/include/stdio.h" 3 4
typedef __off_t off_t;
# 77 "/usr/include/stdio.h" 3 4
typedef __ssize_t ssize_t;
typedef __fpos_t fpos_t;
# 133 "/usr/include/stdio.h" 3 4
# 1 "/usr/include/bits/stdio_lim.h" 1 3 4
# 134 "/usr/include/stdio.h" 2 3 4
# 143 "/usr/include/stdio.h" 3 4
extern FILE *stdin;
extern FILE *stdout;
extern FILE *stderr;
extern int remove (const char *__filename) __attribute__ ((__nothrow__ , __leaf__));
extern int rename (const char *__old, const char *__new) __attribute__ ((__nothrow__ , __leaf__));
extern int renameat (int __oldfd, const char *__old, int __newfd,
const char *__new) __attribute__ ((__nothrow__ , __leaf__));
# 178 "/usr/include/stdio.h" 3 4
extern int fclose (FILE *__stream);
# 188 "/usr/include/stdio.h" 3 4
extern FILE *tmpfile (void)
__attribute__ ((__malloc__)) __attribute__ ((__malloc__ (fclose, 1))) ;
# 205 "/usr/include/stdio.h" 3 4
extern char *tmpnam (char[20]) __attribute__ ((__nothrow__ , __leaf__)) ;
extern char *tmpnam_r (char __s[20]) __attribute__ ((__nothrow__ , __leaf__)) ;
# 222 "/usr/include/stdio.h" 3 4
extern char *tempnam (const char *__dir, const char *__pfx)
__attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__malloc__)) __attribute__ ((__malloc__ (__builtin_free, 1)));
extern int fflush (FILE *__stream);
# 239 "/usr/include/stdio.h" 3 4
extern int fflush_unlocked (FILE *__stream);
# 258 "/usr/include/stdio.h" 3 4
extern FILE *fopen (const char *__restrict __filename,
const char *__restrict __modes)
__attribute__ ((__malloc__)) __attribute__ ((__malloc__ (fclose, 1))) ;
extern FILE *freopen (const char *__restrict __filename,
const char *__restrict __modes,
FILE *__restrict __stream) ;
# 293 "/usr/include/stdio.h" 3 4
extern FILE *fdopen (int __fd, const char *__modes) __attribute__ ((__nothrow__ , __leaf__))
__attribute__ ((__malloc__)) __attribute__ ((__malloc__ (fclose, 1))) ;
# 308 "/usr/include/stdio.h" 3 4
extern FILE *fmemopen (void *__s, size_t __len, const char *__modes)
__attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__malloc__)) __attribute__ ((__malloc__ (fclose, 1))) ;
extern FILE *open_memstream (char **__bufloc, size_t *__sizeloc) __attribute__ ((__nothrow__ , __leaf__))
__attribute__ ((__malloc__)) __attribute__ ((__malloc__ (fclose, 1))) ;
# 328 "/usr/include/stdio.h" 3 4
extern void setbuf (FILE *__restrict __stream, char *__restrict __buf) __attribute__ ((__nothrow__ , __leaf__));
extern int setvbuf (FILE *__restrict __stream, char *__restrict __buf,
int __modes, size_t __n) __attribute__ ((__nothrow__ , __leaf__));
extern void setbuffer (FILE *__restrict __stream, char *__restrict __buf,
size_t __size) __attribute__ ((__nothrow__ , __leaf__));
extern void setlinebuf (FILE *__stream) __attribute__ ((__nothrow__ , __leaf__));
extern int fprintf (FILE *__restrict __stream,
const char *__restrict __format, ...);
extern int printf (const char *__restrict __format, ...);
extern int sprintf (char *__restrict __s,
const char *__restrict __format, ...) __attribute__ ((__nothrow__));
extern int vfprintf (FILE *__restrict __s, const char *__restrict __format,
__gnuc_va_list __arg);
extern int vprintf (const char *__restrict __format, __gnuc_va_list __arg);
extern int vsprintf (char *__restrict __s, const char *__restrict __format,
__gnuc_va_list __arg) __attribute__ ((__nothrow__));
extern int snprintf (char *__restrict __s, size_t __maxlen,
const char *__restrict __format, ...)
__attribute__ ((__nothrow__)) __attribute__ ((__format__ (__printf__, 3, 4)));
extern int vsnprintf (char *__restrict __s, size_t __maxlen,
const char *__restrict __format, __gnuc_va_list __arg)
__attribute__ ((__nothrow__)) __attribute__ ((__format__ (__printf__, 3, 0)));
# 403 "/usr/include/stdio.h" 3 4
extern int vdprintf (int __fd, const char *__restrict __fmt,
__gnuc_va_list __arg)
__attribute__ ((__format__ (__printf__, 2, 0)));
extern int dprintf (int __fd, const char *__restrict __fmt, ...)
__attribute__ ((__format__ (__printf__, 2, 3)));
extern int fscanf (FILE *__restrict __stream,
const char *__restrict __format, ...) ;
extern int scanf (const char *__restrict __format, ...) ;
extern int sscanf (const char *__restrict __s,
const char *__restrict __format, ...) __attribute__ ((__nothrow__ , __leaf__));
# 1 "/usr/include/bits/floatn.h" 1 3 4
# 119 "/usr/include/bits/floatn.h" 3 4
# 1 "/usr/include/bits/floatn-common.h" 1 3 4
# 24 "/usr/include/bits/floatn-common.h" 3 4
# 1 "/usr/include/bits/long-double.h" 1 3 4
# 25 "/usr/include/bits/floatn-common.h" 2 3 4
# 120 "/usr/include/bits/floatn.h" 2 3 4
# 431 "/usr/include/stdio.h" 2 3 4
extern int fscanf (FILE *__restrict __stream, const char *__restrict __format, ...) __asm__ ("" "__isoc99_fscanf")
;
extern int scanf (const char *__restrict __format, ...) __asm__ ("" "__isoc99_scanf")
;
extern int sscanf (const char *__restrict __s, const char *__restrict __format, ...) __asm__ ("" "__isoc99_sscanf") __attribute__ ((__nothrow__ , __leaf__))
;
# 459 "/usr/include/stdio.h" 3 4
extern int vfscanf (FILE *__restrict __s, const char *__restrict __format,
__gnuc_va_list __arg)
__attribute__ ((__format__ (__scanf__, 2, 0))) ;
extern int vscanf (const char *__restrict __format, __gnuc_va_list __arg)
__attribute__ ((__format__ (__scanf__, 1, 0))) ;
extern int vsscanf (const char *__restrict __s,
const char *__restrict __format, __gnuc_va_list __arg)
__attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__format__ (__scanf__, 2, 0)));
extern int vfscanf (FILE *__restrict __s, const char *__restrict __format, __gnuc_va_list __arg) __asm__ ("" "__isoc99_vfscanf")
__attribute__ ((__format__ (__scanf__, 2, 0))) ;
extern int vscanf (const char *__restrict __format, __gnuc_va_list __arg) __asm__ ("" "__isoc99_vscanf")
__attribute__ ((__format__ (__scanf__, 1, 0))) ;
extern int vsscanf (const char *__restrict __s, const char *__restrict __format, __gnuc_va_list __arg) __asm__ ("" "__isoc99_vsscanf") __attribute__ ((__nothrow__ , __leaf__))
__attribute__ ((__format__ (__scanf__, 2, 0)));
# 513 "/usr/include/stdio.h" 3 4
extern int fgetc (FILE *__stream);
extern int getc (FILE *__stream);
extern int getchar (void);
extern int getc_unlocked (FILE *__stream);
extern int getchar_unlocked (void);
# 538 "/usr/include/stdio.h" 3 4
extern int fgetc_unlocked (FILE *__stream);
# 549 "/usr/include/stdio.h" 3 4
extern int fputc (int __c, FILE *__stream);
extern int putc (int __c, FILE *__stream);
extern int putchar (int __c);
# 565 "/usr/include/stdio.h" 3 4
extern int fputc_unlocked (int __c, FILE *__stream);
extern int putc_unlocked (int __c, FILE *__stream);
extern int putchar_unlocked (int __c);
extern int getw (FILE *__stream);
extern int putw (int __w, FILE *__stream);
extern char *fgets (char *__restrict __s, int __n, FILE *__restrict __stream)
__attribute__ ((__access__ (__write_only__, 1, 2)));
# 632 "/usr/include/stdio.h" 3 4
extern __ssize_t __getdelim (char **__restrict __lineptr,
size_t *__restrict __n, int __delimiter,
FILE *__restrict __stream) ;
extern __ssize_t getdelim (char **__restrict __lineptr,
size_t *__restrict __n, int __delimiter,
FILE *__restrict __stream) ;
extern __ssize_t getline (char **__restrict __lineptr,
size_t *__restrict __n,
FILE *__restrict __stream) ;
extern int fputs (const char *__restrict __s, FILE *__restrict __stream);
extern int puts (const char *__s);
extern int ungetc (int __c, FILE *__stream);
extern size_t fread (void *__restrict __ptr, size_t __size,
size_t __n, FILE *__restrict __stream) ;
extern size_t fwrite (const void *__restrict __ptr, size_t __size,
size_t __n, FILE *__restrict __s);
# 702 "/usr/include/stdio.h" 3 4
extern size_t fread_unlocked (void *__restrict __ptr, size_t __size,
size_t __n, FILE *__restrict __stream) ;
extern size_t fwrite_unlocked (const void *__restrict __ptr, size_t __size,
size_t __n, FILE *__restrict __stream);
extern int fseek (FILE *__stream, long int __off, int __whence);
extern long int ftell (FILE *__stream) ;
extern void rewind (FILE *__stream);
# 736 "/usr/include/stdio.h" 3 4
extern int fseeko (FILE *__stream, __off_t __off, int __whence);
extern __off_t ftello (FILE *__stream) ;
# 760 "/usr/include/stdio.h" 3 4
extern int fgetpos (FILE *__restrict __stream, fpos_t *__restrict __pos);
extern int fsetpos (FILE *__stream, const fpos_t *__pos);
# 786 "/usr/include/stdio.h" 3 4
extern void clearerr (FILE *__stream) __attribute__ ((__nothrow__ , __leaf__));
extern int feof (FILE *__stream) __attribute__ ((__nothrow__ , __leaf__)) ;
extern int ferror (FILE *__stream) __attribute__ ((__nothrow__ , __leaf__)) ;
extern void clearerr_unlocked (FILE *__stream) __attribute__ ((__nothrow__ , __leaf__));
extern int feof_unlocked (FILE *__stream) __attribute__ ((__nothrow__ , __leaf__)) ;
extern int ferror_unlocked (FILE *__stream) __attribute__ ((__nothrow__ , __leaf__)) ;
extern void perror (const char *__s);
extern int fileno (FILE *__stream) __attribute__ ((__nothrow__ , __leaf__)) ;
extern int fileno_unlocked (FILE *__stream) __attribute__ ((__nothrow__ , __leaf__)) ;
# 823 "/usr/include/stdio.h" 3 4
extern int pclose (FILE *__stream);
extern FILE *popen (const char *__command, const char *__modes)
__attribute__ ((__malloc__)) __attribute__ ((__malloc__ (pclose, 1))) ;
extern char *ctermid (char *__s) __attribute__ ((__nothrow__ , __leaf__))
__attribute__ ((__access__ (__write_only__, 1)));
# 867 "/usr/include/stdio.h" 3 4
extern void flockfile (FILE *__stream) __attribute__ ((__nothrow__ , __leaf__));
extern int ftrylockfile (FILE *__stream) __attribute__ ((__nothrow__ , __leaf__)) ;
extern void funlockfile (FILE *__stream) __attribute__ ((__nothrow__ , __leaf__));
# 885 "/usr/include/stdio.h" 3 4
extern int __uflow (FILE *);
extern int __overflow (FILE *, int);
# 902 "/usr/include/stdio.h" 3 4
# 2 "main.c" 2
# 1 "/usr/include/stdlib.h" 1 3 4
# 26 "/usr/include/stdlib.h" 3 4
# 1 "/usr/include/bits/libc-header-start.h" 1 3 4
# 27 "/usr/include/stdlib.h" 2 3 4
# 1 "/usr/lib/gcc/x86_64-pc-linux-gnu/12.1.0/include/stddef.h" 1 3 4
# 329 "/usr/lib/gcc/x86_64-pc-linux-gnu/12.1.0/include/stddef.h" 3 4
typedef int wchar_t;
# 33 "/usr/include/stdlib.h" 2 3 4
# 1 "/usr/include/bits/waitflags.h" 1 3 4
# 41 "/usr/include/stdlib.h" 2 3 4
# 1 "/usr/include/bits/waitstatus.h" 1 3 4
# 42 "/usr/include/stdlib.h" 2 3 4
# 59 "/usr/include/stdlib.h" 3 4
typedef struct
{
int quot;
int rem;
} div_t;
typedef struct
{
long int quot;
long int rem;
} ldiv_t;
__extension__ typedef struct
{
long long int quot;
long long int rem;
} lldiv_t;
# 98 "/usr/include/stdlib.h" 3 4
extern size_t __ctype_get_mb_cur_max (void) __attribute__ ((__nothrow__ , __leaf__)) ;
extern double atof (const char *__nptr)
__attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__pure__)) __attribute__ ((__nonnull__ (1))) ;
extern int atoi (const char *__nptr)
__attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__pure__)) __attribute__ ((__nonnull__ (1))) ;
extern long int atol (const char *__nptr)
__attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__pure__)) __attribute__ ((__nonnull__ (1))) ;
__extension__ extern long long int atoll (const char *__nptr)
__attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__pure__)) __attribute__ ((__nonnull__ (1))) ;
extern double strtod (const char *__restrict __nptr,
char **__restrict __endptr)
__attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (1)));
extern float strtof (const char *__restrict __nptr,
char **__restrict __endptr) __attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (1)));
extern long double strtold (const char *__restrict __nptr,
char **__restrict __endptr)
__attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (1)));
# 177 "/usr/include/stdlib.h" 3 4
extern long int strtol (const char *__restrict __nptr,
char **__restrict __endptr, int __base)
__attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (1)));
extern unsigned long int strtoul (const char *__restrict __nptr,
char **__restrict __endptr, int __base)
__attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (1)));
__extension__
extern long long int strtoq (const char *__restrict __nptr,
char **__restrict __endptr, int __base)
__attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (1)));
__extension__
extern unsigned long long int strtouq (const char *__restrict __nptr,
char **__restrict __endptr, int __base)
__attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (1)));
__extension__
extern long long int strtoll (const char *__restrict __nptr,
char **__restrict __endptr, int __base)
__attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (1)));
__extension__
extern unsigned long long int strtoull (const char *__restrict __nptr,
char **__restrict __endptr, int __base)
__attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (1)));
# 386 "/usr/include/stdlib.h" 3 4
extern char *l64a (long int __n) __attribute__ ((__nothrow__ , __leaf__)) ;
extern long int a64l (const char *__s)
__attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__pure__)) __attribute__ ((__nonnull__ (1))) ;
# 1 "/usr/include/sys/types.h" 1 3 4
# 27 "/usr/include/sys/types.h" 3 4
typedef __u_char u_char;
typedef __u_short u_short;
typedef __u_int u_int;
typedef __u_long u_long;
typedef __quad_t quad_t;
typedef __u_quad_t u_quad_t;
typedef __fsid_t fsid_t;
typedef __loff_t loff_t;
typedef __ino_t ino_t;
# 59 "/usr/include/sys/types.h" 3 4
typedef __dev_t dev_t;
typedef __gid_t gid_t;
typedef __mode_t mode_t;
typedef __nlink_t nlink_t;
typedef __uid_t uid_t;
# 97 "/usr/include/sys/types.h" 3 4
typedef __pid_t pid_t;
typedef __id_t id_t;
# 114 "/usr/include/sys/types.h" 3 4
typedef __daddr_t daddr_t;
typedef __caddr_t caddr_t;
typedef __key_t key_t;
# 1 "/usr/include/bits/types/clock_t.h" 1 3 4
typedef __clock_t clock_t;
# 127 "/usr/include/sys/types.h" 2 3 4
# 1 "/usr/include/bits/types/clockid_t.h" 1 3 4
typedef __clockid_t clockid_t;
# 129 "/usr/include/sys/types.h" 2 3 4
# 1 "/usr/include/bits/types/time_t.h" 1 3 4
# 10 "/usr/include/bits/types/time_t.h" 3 4
typedef __time_t time_t;
# 130 "/usr/include/sys/types.h" 2 3 4
# 1 "/usr/include/bits/types/timer_t.h" 1 3 4
typedef __timer_t timer_t;
# 131 "/usr/include/sys/types.h" 2 3 4
# 144 "/usr/include/sys/types.h" 3 4
# 1 "/usr/lib/gcc/x86_64-pc-linux-gnu/12.1.0/include/stddef.h" 1 3 4
# 145 "/usr/include/sys/types.h" 2 3 4
typedef unsigned long int ulong;
typedef unsigned short int ushort;
typedef unsigned int uint;
# 1 "/usr/include/bits/stdint-intn.h" 1 3 4
# 24 "/usr/include/bits/stdint-intn.h" 3 4
typedef __int8_t int8_t;
typedef __int16_t int16_t;
typedef __int32_t int32_t;
typedef __int64_t int64_t;
# 156 "/usr/include/sys/types.h" 2 3 4
typedef __uint8_t u_int8_t;
typedef __uint16_t u_int16_t;
typedef __uint32_t u_int32_t;
typedef __uint64_t u_int64_t;
typedef int register_t __attribute__ ((__mode__ (__word__)));
# 176 "/usr/include/sys/types.h" 3 4
# 1 "/usr/include/endian.h" 1 3 4
# 24 "/usr/include/endian.h" 3 4
# 1 "/usr/include/bits/endian.h" 1 3 4
# 35 "/usr/include/bits/endian.h" 3 4
# 1 "/usr/include/bits/endianness.h" 1 3 4
# 36 "/usr/include/bits/endian.h" 2 3 4
# 25 "/usr/include/endian.h" 2 3 4
# 35 "/usr/include/endian.h" 3 4
# 1 "/usr/include/bits/byteswap.h" 1 3 4
# 33 "/usr/include/bits/byteswap.h" 3 4
static __inline __uint16_t
__bswap_16 (__uint16_t __bsx)
{
return __builtin_bswap16 (__bsx);
}
static __inline __uint32_t
__bswap_32 (__uint32_t __bsx)
{
return __builtin_bswap32 (__bsx);
}
# 69 "/usr/include/bits/byteswap.h" 3 4
__extension__ static __inline __uint64_t
__bswap_64 (__uint64_t __bsx)
{
return __builtin_bswap64 (__bsx);
}
# 36 "/usr/include/endian.h" 2 3 4
# 1 "/usr/include/bits/uintn-identity.h" 1 3 4
# 32 "/usr/include/bits/uintn-identity.h" 3 4
static __inline __uint16_t
__uint16_identity (__uint16_t __x)
{
return __x;
}
static __inline __uint32_t
__uint32_identity (__uint32_t __x)
{
return __x;
}
static __inline __uint64_t
__uint64_identity (__uint64_t __x)
{
return __x;
}
# 37 "/usr/include/endian.h" 2 3 4
# 177 "/usr/include/sys/types.h" 2 3 4
# 1 "/usr/include/sys/select.h" 1 3 4
# 30 "/usr/include/sys/select.h" 3 4
# 1 "/usr/include/bits/select.h" 1 3 4
# 31 "/usr/include/sys/select.h" 2 3 4
# 1 "/usr/include/bits/types/sigset_t.h" 1 3 4
# 1 "/usr/include/bits/types/__sigset_t.h" 1 3 4
typedef struct
{
unsigned long int __val[(1024 / (8 * sizeof (unsigned long int)))];
} __sigset_t;
# 5 "/usr/include/bits/types/sigset_t.h" 2 3 4
typedef __sigset_t sigset_t;
# 34 "/usr/include/sys/select.h" 2 3 4
# 1 "/usr/include/bits/types/struct_timeval.h" 1 3 4
struct timeval
{
__time_t tv_sec;
__suseconds_t tv_usec;
};
# 38 "/usr/include/sys/select.h" 2 3 4
# 1 "/usr/include/bits/types/struct_timespec.h" 1 3 4
# 11 "/usr/include/bits/types/struct_timespec.h" 3 4
struct timespec
{
__time_t tv_sec;
__syscall_slong_t tv_nsec;
# 31 "/usr/include/bits/types/struct_timespec.h" 3 4
};
# 40 "/usr/include/sys/select.h" 2 3 4
typedef __suseconds_t suseconds_t;
typedef long int __fd_mask;
# 59 "/usr/include/sys/select.h" 3 4
typedef struct
{
__fd_mask __fds_bits[1024 / (8 * (int) sizeof (__fd_mask))];
} fd_set;
typedef __fd_mask fd_mask;
# 91 "/usr/include/sys/select.h" 3 4
# 102 "/usr/include/sys/select.h" 3 4
extern int select (int __nfds, fd_set *__restrict __readfds,
fd_set *__restrict __writefds,
fd_set *__restrict __exceptfds,
struct timeval *__restrict __timeout);
# 127 "/usr/include/sys/select.h" 3 4
extern int pselect (int __nfds, fd_set *__restrict __readfds,
fd_set *__restrict __writefds,
fd_set *__restrict __exceptfds,
const struct timespec *__restrict __timeout,
const __sigset_t *__restrict __sigmask);
# 153 "/usr/include/sys/select.h" 3 4
# 180 "/usr/include/sys/types.h" 2 3 4
typedef __blksize_t blksize_t;
typedef __blkcnt_t blkcnt_t;
typedef __fsblkcnt_t fsblkcnt_t;
typedef __fsfilcnt_t fsfilcnt_t;
# 227 "/usr/include/sys/types.h" 3 4
# 1 "/usr/include/bits/pthreadtypes.h" 1 3 4
# 23 "/usr/include/bits/pthreadtypes.h" 3 4
# 1 "/usr/include/bits/thread-shared-types.h" 1 3 4
# 44 "/usr/include/bits/thread-shared-types.h" 3 4
# 1 "/usr/include/bits/pthreadtypes-arch.h" 1 3 4
# 21 "/usr/include/bits/pthreadtypes-arch.h" 3 4
# 1 "/usr/include/bits/wordsize.h" 1 3 4
# 22 "/usr/include/bits/pthreadtypes-arch.h" 2 3 4
# 45 "/usr/include/bits/thread-shared-types.h" 2 3 4
# 1 "/usr/include/bits/atomic_wide_counter.h" 1 3 4
# 25 "/usr/include/bits/atomic_wide_counter.h" 3 4
typedef union
{
__extension__ unsigned long long int __value64;
struct
{
unsigned int __low;
unsigned int __high;
} __value32;
} __atomic_wide_counter;
# 47 "/usr/include/bits/thread-shared-types.h" 2 3 4
typedef struct __pthread_internal_list
{
struct __pthread_internal_list *__prev;
struct __pthread_internal_list *__next;
} __pthread_list_t;
typedef struct __pthread_internal_slist
{
struct __pthread_internal_slist *__next;
} __pthread_slist_t;
# 76 "/usr/include/bits/thread-shared-types.h" 3 4
# 1 "/usr/include/bits/struct_mutex.h" 1 3 4
# 22 "/usr/include/bits/struct_mutex.h" 3 4
struct __pthread_mutex_s
{
int __lock;
unsigned int __count;
int __owner;
unsigned int __nusers;
int __kind;
short __spins;
short __elision;
__pthread_list_t __list;
# 53 "/usr/include/bits/struct_mutex.h" 3 4
};
# 77 "/usr/include/bits/thread-shared-types.h" 2 3 4
# 89 "/usr/include/bits/thread-shared-types.h" 3 4
# 1 "/usr/include/bits/struct_rwlock.h" 1 3 4
# 23 "/usr/include/bits/struct_rwlock.h" 3 4
struct __pthread_rwlock_arch_t
{
unsigned int __readers;
unsigned int __writers;
unsigned int __wrphase_futex;
unsigned int __writers_futex;
unsigned int __pad3;
unsigned int __pad4;
int __cur_writer;
int __shared;
signed char __rwelision;
unsigned char __pad1[7];
unsigned long int __pad2;
unsigned int __flags;
# 55 "/usr/include/bits/struct_rwlock.h" 3 4
};
# 90 "/usr/include/bits/thread-shared-types.h" 2 3 4
struct __pthread_cond_s
{
__atomic_wide_counter __wseq;
__atomic_wide_counter __g1_start;
unsigned int __g_refs[2] ;
unsigned int __g_size[2];
unsigned int __g1_orig_size;
unsigned int __wrefs;
unsigned int __g_signals[2];
};
typedef unsigned int __tss_t;
typedef unsigned long int __thrd_t;
typedef struct
{
int __data ;
} __once_flag;
# 24 "/usr/include/bits/pthreadtypes.h" 2 3 4
typedef unsigned long int pthread_t;
typedef union
{
char __size[4];
int __align;
} pthread_mutexattr_t;
typedef union
{
char __size[4];
int __align;
} pthread_condattr_t;
typedef unsigned int pthread_key_t;
typedef int pthread_once_t;
union pthread_attr_t
{
char __size[56];
long int __align;
};
typedef union pthread_attr_t pthread_attr_t;
typedef union
{
struct __pthread_mutex_s __data;
char __size[40];
long int __align;
} pthread_mutex_t;
typedef union
{
struct __pthread_cond_s __data;
char __size[48];
__extension__ long long int __align;
} pthread_cond_t;
typedef union
{
struct __pthread_rwlock_arch_t __data;
char __size[56];
long int __align;
} pthread_rwlock_t;
typedef union
{
char __size[8];
long int __align;
} pthread_rwlockattr_t;
typedef volatile int pthread_spinlock_t;
typedef union
{
char __size[32];
long int __align;
} pthread_barrier_t;
typedef union
{
char __size[4];
int __align;
} pthread_barrierattr_t;
# 228 "/usr/include/sys/types.h" 2 3 4
# 396 "/usr/include/stdlib.h" 2 3 4
extern long int random (void) __attribute__ ((__nothrow__ , __leaf__));
extern void srandom (unsigned int __seed) __attribute__ ((__nothrow__ , __leaf__));
extern char *initstate (unsigned int __seed, char *__statebuf,
size_t __statelen) __attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (2)));
extern char *setstate (char *__statebuf) __attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (1)));
struct random_data
{
int32_t *fptr;
int32_t *rptr;
int32_t *state;
int rand_type;
int rand_deg;
int rand_sep;
int32_t *end_ptr;
};
extern int random_r (struct random_data *__restrict __buf,
int32_t *__restrict __result) __attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (1, 2)));
extern int srandom_r (unsigned int __seed, struct random_data *__buf)
__attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (2)));
extern int initstate_r (unsigned int __seed, char *__restrict __statebuf,
size_t __statelen,
struct random_data *__restrict __buf)
__attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (2, 4)));
extern int setstate_r (char *__restrict __statebuf,
struct random_data *__restrict __buf)
__attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (1, 2)));
extern int rand (void) __attribute__ ((__nothrow__ , __leaf__));
extern void srand (unsigned int __seed) __attribute__ ((__nothrow__ , __leaf__));
extern int rand_r (unsigned int *__seed) __attribute__ ((__nothrow__ , __leaf__));
extern double drand48 (void) __attribute__ ((__nothrow__ , __leaf__));
extern double erand48 (unsigned short int __xsubi[3]) __attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (1)));
extern long int lrand48 (void) __attribute__ ((__nothrow__ , __leaf__));
extern long int nrand48 (unsigned short int __xsubi[3])
__attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (1)));
extern long int mrand48 (void) __attribute__ ((__nothrow__ , __leaf__));
extern long int jrand48 (unsigned short int __xsubi[3])
__attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (1)));
extern void srand48 (long int __seedval) __attribute__ ((__nothrow__ , __leaf__));
extern unsigned short int *seed48 (unsigned short int __seed16v[3])
__attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (1)));
extern void lcong48 (unsigned short int __param[7]) __attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (1)));
struct drand48_data
{
unsigned short int __x[3];
unsigned short int __old_x[3];
unsigned short int __c;
unsigned short int __init;
__extension__ unsigned long long int __a;
};
extern int drand48_r (struct drand48_data *__restrict __buffer,
double *__restrict __result) __attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (1, 2)));
extern int erand48_r (unsigned short int __xsubi[3],
struct drand48_data *__restrict __buffer,
double *__restrict __result) __attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (1, 2)));
extern int lrand48_r (struct drand48_data *__restrict __buffer,
long int *__restrict __result)
__attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (1, 2)));
extern int nrand48_r (unsigned short int __xsubi[3],
struct drand48_data *__restrict __buffer,
long int *__restrict __result)
__attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (1, 2)));
extern int mrand48_r (struct drand48_data *__restrict __buffer,
long int *__restrict __result)
__attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (1, 2)));
extern int jrand48_r (unsigned short int __xsubi[3],
struct drand48_data *__restrict __buffer,
long int *__restrict __result)
__attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (1, 2)));
extern int srand48_r (long int __seedval, struct drand48_data *__buffer)
__attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (2)));
extern int seed48_r (unsigned short int __seed16v[3],
struct drand48_data *__buffer) __attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (1, 2)));
extern int lcong48_r (unsigned short int __param[7],
struct drand48_data *__buffer)
__attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (1, 2)));
extern void *malloc (size_t __size) __attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__malloc__))
__attribute__ ((__alloc_size__ (1))) ;
extern void *calloc (size_t __nmemb, size_t __size)
__attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__malloc__)) __attribute__ ((__alloc_size__ (1, 2))) ;
extern void *realloc (void *__ptr, size_t __size)
__attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__warn_unused_result__)) __attribute__ ((__alloc_size__ (2)));
extern void free (void *__ptr) __attribute__ ((__nothrow__ , __leaf__));
extern void *reallocarray (void *__ptr, size_t __nmemb, size_t __size)
__attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__warn_unused_result__))
__attribute__ ((__alloc_size__ (2, 3)))
__attribute__ ((__malloc__ (__builtin_free, 1)));
extern void *reallocarray (void *__ptr, size_t __nmemb, size_t __size)
__attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__malloc__ (reallocarray, 1)));
# 1 "/usr/include/alloca.h" 1 3 4
# 24 "/usr/include/alloca.h" 3 4
# 1 "/usr/lib/gcc/x86_64-pc-linux-gnu/12.1.0/include/stddef.h" 1 3 4
# 25 "/usr/include/alloca.h" 2 3 4
extern void *alloca (size_t __size) __attribute__ ((__nothrow__ , __leaf__));
# 575 "/usr/include/stdlib.h" 2 3 4
extern void *valloc (size_t __size) __attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__malloc__))
__attribute__ ((__alloc_size__ (1))) ;
extern int posix_memalign (void **__memptr, size_t __alignment, size_t __size)
__attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (1))) ;
extern void *aligned_alloc (size_t __alignment, size_t __size)
__attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__malloc__)) __attribute__ ((__alloc_align__ (1)))
__attribute__ ((__alloc_size__ (2))) ;
extern void abort (void) __attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__noreturn__));
extern int atexit (void (*__func) (void)) __attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (1)));
extern int at_quick_exit (void (*__func) (void)) __attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (1)));
extern int on_exit (void (*__func) (int __status, void *__arg), void *__arg)
__attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (1)));
extern void exit (int __status) __attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__noreturn__));
extern void quick_exit (int __status) __attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__noreturn__));
extern void _Exit (int __status) __attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__noreturn__));
extern char *getenv (const char *__name) __attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (1))) ;
# 654 "/usr/include/stdlib.h" 3 4
extern int putenv (char *__string) __attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (1)));
extern int setenv (const char *__name, const char *__value, int __replace)
__attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (2)));
extern int unsetenv (const char *__name) __attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (1)));
extern int clearenv (void) __attribute__ ((__nothrow__ , __leaf__));
# 682 "/usr/include/stdlib.h" 3 4
extern char *mktemp (char *__template) __attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (1)));
# 695 "/usr/include/stdlib.h" 3 4
extern int mkstemp (char *__template) __attribute__ ((__nonnull__ (1))) ;
# 717 "/usr/include/stdlib.h" 3 4
extern int mkstemps (char *__template, int __suffixlen) __attribute__ ((__nonnull__ (1))) ;
# 738 "/usr/include/stdlib.h" 3 4
extern char *mkdtemp (char *__template) __attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (1))) ;
# 791 "/usr/include/stdlib.h" 3 4
extern int system (const char *__command) ;
# 808 "/usr/include/stdlib.h" 3 4
extern char *realpath (const char *__restrict __name,
char *__restrict __resolved) __attribute__ ((__nothrow__ , __leaf__)) ;
typedef int (*__compar_fn_t) (const void *, const void *);
# 828 "/usr/include/stdlib.h" 3 4
extern void *bsearch (const void *__key, const void *__base,
size_t __nmemb, size_t __size, __compar_fn_t __compar)
__attribute__ ((__nonnull__ (1, 2, 5))) ;
extern void qsort (void *__base, size_t __nmemb, size_t __size,
__compar_fn_t __compar) __attribute__ ((__nonnull__ (1, 4)));
# 848 "/usr/include/stdlib.h" 3 4
extern int abs (int __x) __attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__const__)) ;
extern long int labs (long int __x) __attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__const__)) ;
__extension__ extern long long int llabs (long long int __x)
__attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__const__)) ;
extern div_t div (int __numer, int __denom)
__attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__const__)) ;
extern ldiv_t ldiv (long int __numer, long int __denom)
__attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__const__)) ;
__extension__ extern lldiv_t lldiv (long long int __numer,
long long int __denom)
__attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__const__)) ;
# 880 "/usr/include/stdlib.h" 3 4
extern char *ecvt (double __value, int __ndigit, int *__restrict __decpt,
int *__restrict __sign) __attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (3, 4))) ;
extern char *fcvt (double __value, int __ndigit, int *__restrict __decpt,
int *__restrict __sign) __attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (3, 4))) ;
extern char *gcvt (double __value, int __ndigit, char *__buf)
__attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (3))) ;
extern char *qecvt (long double __value, int __ndigit,
int *__restrict __decpt, int *__restrict __sign)
__attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (3, 4))) ;
extern char *qfcvt (long double __value, int __ndigit,
int *__restrict __decpt, int *__restrict __sign)
__attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (3, 4))) ;
extern char *qgcvt (long double __value, int __ndigit, char *__buf)
__attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (3))) ;
extern int ecvt_r (double __value, int __ndigit, int *__restrict __decpt,
int *__restrict __sign, char *__restrict __buf,
size_t __len) __attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (3, 4, 5)));
extern int fcvt_r (double __value, int __ndigit, int *__restrict __decpt,
int *__restrict __sign, char *__restrict __buf,
size_t __len) __attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (3, 4, 5)));
extern int qecvt_r (long double __value, int __ndigit,
int *__restrict __decpt, int *__restrict __sign,
char *__restrict __buf, size_t __len)
__attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (3, 4, 5)));
extern int qfcvt_r (long double __value, int __ndigit,
int *__restrict __decpt, int *__restrict __sign,
char *__restrict __buf, size_t __len)
__attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (3, 4, 5)));
extern int mblen (const char *__s, size_t __n) __attribute__ ((__nothrow__ , __leaf__));
extern int mbtowc (wchar_t *__restrict __pwc,
const char *__restrict __s, size_t __n) __attribute__ ((__nothrow__ , __leaf__));
extern int wctomb (char *__s, wchar_t __wchar) __attribute__ ((__nothrow__ , __leaf__));
extern size_t mbstowcs (wchar_t *__restrict __pwcs,
const char *__restrict __s, size_t __n) __attribute__ ((__nothrow__ , __leaf__))
__attribute__ ((__access__ (__read_only__, 2)));
extern size_t wcstombs (char *__restrict __s,
const wchar_t *__restrict __pwcs, size_t __n)
__attribute__ ((__nothrow__ , __leaf__))
__attribute__ ((__access__ (__write_only__, 1, 3)))
__attribute__ ((__access__ (__read_only__, 2)));
extern int rpmatch (const char *__response) __attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (1))) ;
# 967 "/usr/include/stdlib.h" 3 4
extern int getsubopt (char **__restrict __optionp,
char *const *__restrict __tokens,
char **__restrict __valuep)
__attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (1, 2, 3))) ;
# 1013 "/usr/include/stdlib.h" 3 4
extern int getloadavg (double __loadavg[], int __nelem)
__attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (1)));
# 1023 "/usr/include/stdlib.h" 3 4
# 1 "/usr/include/bits/stdlib-float.h" 1 3 4
# 1024 "/usr/include/stdlib.h" 2 3 4
# 1035 "/usr/include/stdlib.h" 3 4
# 3 "main.c" 2
# 7 "main.c"
int main() {
printf("Hello world\n");
printf("%d\n", 10);
return
# 10 "main.c" 3 4
0
# 10 "main.c"
;
}
There is a CPP tool, which stands for C Pre-Processor, which is used to pre-process a C file.
The C preprocessor or cpp is the macro preprocessor for the C, Objective-C, and C++ computer programming languages. The preprocessor provides the ability for the inclusion of header files, macro expansions, conditional compilation, and line control.
cpp main.c
This command will provide you the preprocessed code for the c program.
The preprocessed file has an extension of .i, and if you pass this file to the C compiler driver, the preprocessor stage will be bypassed. This happens because of the file with the .i extension is supposed to have already been preprocessed and is sent directly to the compilation stage.
Step 2 – Compilation
In the previous section, we had our Translation Unit, and now we can move on to our next step, i.e. the compilation of the Translation Unit Code.
The input for the compilation component is the translation unit, obtained from the previous component. The output from the compilation component is the assembly code (Still Human-readable code, but closer to the hardware).
Extract Assembly Code from GCC
As in the previous stage, we dumped the translation unit code using the -E option. Here, we can use the -S option for the GCC to obtain the assembly code. This will create a file with the .s extension, and we will see the contents of the file using the cat command.
generate asm from c src
gcc -S main.c -o main.s
.file "main.c"
.text
.section .rodata
.LC0:
.string "Hello world"
.LC1:
.string "%d\n"
.text
.globl main
.type main, @function
main:
.LFB6:
.cfi_startproc
pushq %rbp
.cfi_def_cfa_offset 16
.cfi_offset 6, -16
movq %rsp, %rbp
.cfi_def_cfa_register 6
leaq .LC0(%rip), %rax
movq %rax, %rdi
call puts@PLT
movl $10, %esi
leaq .LC1(%rip), %rax
movq %rax, %rdi
movl $0, %eax
call printf@PLT
movl $0, %eax
popq %rbp
.cfi_def_cfa 7, 8
ret
.cfi_endproc
.LFE6:
.size main, .-main
.ident "GCC: (GNU) 12.1.0"
.section .note.GNU-stack,"",@progbits
The Compilation phase gives us the Assembly code that is unique to the target architecture.
Even if the C language compiler is the same for two different machines with the same C program but different processors and hardware, different assembly codes would be produced.
Generating the assembly code from the C code is one of the most critical stages in the C Program Compilation Pipeline since the assembly code is a low-level language that can be translated to an object file using an assembler.
Step 3 – Assembly
The Compilation stage gives us the assembly code that is the input for the next pipeline component, i.e. assembly.
In this stage, the actual instructions on the machine level are generated from the assembly code. Each architecture has its own assembler, which converts its own assembly code into its own machine code.
The assembler generates a relocatable object file from the assembly code.
Create Object file from the Assembly file
create object file from asm
as main.s -o main.o
This is really helpful when you want to work with object files and repeating all of the above steps can be quite hectic for a number of files.
The contents inside the object file contain low-level code and are thus not readable to humans. In the latter portion, we will also learn about a tool that will allow us to see the contents of an object file.
Now that we know how to build object files directly from both the assembly file and the C program. It’s time to learn about the Linking Stage in the C program compilation process.
Step 4 – Linking
This is one of the most critical steps in the C compilation pipeline where the generated relocatable object files are combined/linked to create another object file that is executable in nature.
Let’s take a look at the situation.
Suppose we have a custom header file example.h, which contains a printRef function prototype, and a source file example.c, which contains the function definition of the header file.
example.c
#include "example.h"
void printRef() { printf("printRef defined here"); }
example.h
void printRef();
main.c
#include "example.h"
#include <stdlib.h>
int main() {
printRef();
return EXIT_SUCCESS;
}
As we know there are two source files, and we’ll have to generate separate object files, which will be linked by the linker later to provide us an executable object file.
gcc -c main.c -o main.o
gcc -c example.c example.o
Now we need to link the object files together:
link object files with gcc
gcc example.o main.o -o a.out
tip
if you now want to change the implementation of printRef you would only need to recompile that single file and link it again. There is a tool for handling this process automatically GNU Make.
Analysis of Object Files
The nm tool is used to display symbols that can be found in an object file.
nm -a example.o
0000000000000000 a example.c
0000000000000000 T printRef
U puts
0000000000000000 r .rodata
0000000000000000 t .text
nm -a main.o
0000000000000000 T main
0000000000000000 a main.c
U printRef
0000000000000000 t .text
nm -a a.out
0000000000000000 a
0000000000000000 a abi-note.c
000000000000039c r __abi_tag
0000000000004030 B __bss_start
0000000000004030 b completed.0
0000000000000000 a crtstuff.c
0000000000000000 a crtstuff.c
w __cxa_finalize@GLIBC_2.2.5
0000000000004020 D __data_start
0000000000004020 W data_start
0000000000001070 t deregister_tm_clones
00000000000010e0 t __do_global_dtors_aux
0000000000003df0 d __do_global_dtors_aux_fini_array_entry
0000000000004028 D __dso_handle
0000000000003df8 d _DYNAMIC
0000000000004030 D _edata
0000000000004038 B _end
0000000000000000 a example.c
0000000000001164 T _fini
0000000000001130 t frame_dummy
0000000000003de8 d __frame_dummy_init_array_entry
00000000000020e0 r __FRAME_END__
0000000000004000 d _GLOBAL_OFFSET_TABLE_
w __gmon_start__
000000000000201c r __GNU_EH_FRAME_HDR
0000000000001000 T _init
0000000000000000 a init.c
0000000000002000 R _IO_stdin_used
w _ITM_deregisterTMCloneTable
w _ITM_registerTMCloneTable
U __libc_start_main@GLIBC_2.34
0000000000001139 T main
0000000000000000 a main.c
000000000000114e T printRef
U puts@GLIBC_2.2.5
00000000000010a0 t register_tm_clones
0000000000001040 T _start
0000000000004030 D __TMC_END__
The object module provides all the details required to relocate and link the application to another program.
ELF
The ELF header at the top of this table defines the ELF file. The next section is a section header table containing details on all parts in the ELF file.
Let’s Understand the Four important Sections in the ELF File.
- .text – Our c program is stored in this section. We only have read and execute permission to this section and not write permission.
- .data – All initialized global and static variables are stored in the .data section. (Read and Write Permission)
- .rodata – Constants and literals are stored in the .rodata section. (Read Permission)
- .bss – This section contains uninitialized global and static variables. (Read and Write Permission)
To see the content of the generated executable use the readelf tool.
read ELF
readelf -a a.out
ELF Header:
Magic: 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00
Class: ELF64
Data: 2's complement, little endian
Version: 1 (current)
OS/ABI: UNIX - System V
ABI Version: 0
Type: DYN (Position-Independent Executable file)
Machine: Advanced Micro Devices X86-64
Version: 0x1
Entry point address: 0x1040
Start of program headers: 64 (bytes into file)
Start of section headers: 18240 (bytes into file)
Flags: 0x0
Size of this header: 64 (bytes)
Size of program headers: 56 (bytes)
Number of program headers: 13
Size of section headers: 64 (bytes)
Number of section headers: 37
Section header string table index: 36
Section Headers:
[Nr] Name Type Address Offset
Size EntSize Flags Link Info Align
[ 0] NULL 0000000000000000 00000000
0000000000000000 0000000000000000 0 0 0
[ 1] .interp PROGBITS 0000000000000318 00000318
000000000000001c 0000000000000000 A 0 0 1
[ 2] .note.gnu.pr[...] NOTE 0000000000000338 00000338
0000000000000040 0000000000000000 A 0 0 8
[ 3] .note.gnu.bu[...] NOTE 0000000000000378 00000378
0000000000000024 0000000000000000 A 0 0 4
[ 4] .note.ABI-tag NOTE 000000000000039c 0000039c
0000000000000020 0000000000000000 A 0 0 4
[ 5] .gnu.hash GNU_HASH 00000000000003c0 000003c0
000000000000001c 0000000000000000 A 6 0 8
[ 6] .dynsym DYNSYM 00000000000003e0 000003e0
00000000000000a8 0000000000000018 A 7 1 8
[ 7] .dynstr STRTAB 0000000000000488 00000488
000000000000008d 0000000000000000 A 0 0 1
[ 8] .gnu.version VERSYM 0000000000000516 00000516
000000000000000e 0000000000000002 A 6 0 2
[ 9] .gnu.version_r VERNEED 0000000000000528 00000528
0000000000000030 0000000000000000 A 7 1 8
[10] .rela.dyn RELA 0000000000000558 00000558
00000000000000c0 0000000000000018 A 6 0 8
[11] .rela.plt RELA 0000000000000618 00000618
0000000000000018 0000000000000018 AI 6 23 8
[12] .init PROGBITS 0000000000001000 00001000
000000000000001b 0000000000000000 AX 0 0 4
[13] .plt PROGBITS 0000000000001020 00001020
0000000000000020 0000000000000010 AX 0 0 16
[14] .text PROGBITS 0000000000001040 00001040
0000000000000124 0000000000000000 AX 0 0 16
[15] .fini PROGBITS 0000000000001164 00001164
000000000000000d 0000000000000000 AX 0 0 4
[16] .rodata PROGBITS 0000000000002000 00002000
000000000000001a 0000000000000000 A 0 0 4
[17] .eh_frame_hdr PROGBITS 000000000000201c 0000201c
000000000000002c 0000000000000000 A 0 0 4
[18] .eh_frame PROGBITS 0000000000002048 00002048
000000000000009c 0000000000000000 A 0 0 8
[19] .init_array INIT_ARRAY 0000000000003de8 00002de8
0000000000000008 0000000000000008 WA 0 0 8
[20] .fini_array FINI_ARRAY 0000000000003df0 00002df0
0000000000000008 0000000000000008 WA 0 0 8
[21] .dynamic DYNAMIC 0000000000003df8 00002df8
00000000000001e0 0000000000000010 WA 7 0 8
[22] .got PROGBITS 0000000000003fd8 00002fd8
0000000000000028 0000000000000008 WA 0 0 8
[23] .got.plt PROGBITS 0000000000004000 00003000
0000000000000020 0000000000000008 WA 0 0 8
[24] .data PROGBITS 0000000000004020 00003020
0000000000000010 0000000000000000 WA 0 0 8
[25] .bss NOBITS 0000000000004030 00003030
0000000000000008 0000000000000000 WA 0 0 1
[26] .comment PROGBITS 0000000000000000 00003030
0000000000000012 0000000000000001 MS 0 0 1
[27] .debug_aranges PROGBITS 0000000000000000 00003050
00000000000000f0 0000000000000000 0 0 16
[28] .debug_info PROGBITS 0000000000000000 00003140
0000000000000585 0000000000000000 0 0 1
[29] .debug_abbrev PROGBITS 0000000000000000 000036c5
0000000000000198 0000000000000000 0 0 1
[30] .debug_line PROGBITS 0000000000000000 0000385d
00000000000001da 0000000000000000 0 0 1
[31] .debug_str PROGBITS 0000000000000000 00003a37
0000000000000471 0000000000000001 MS 0 0 1
[32] .debug_line_str PROGBITS 0000000000000000 00003ea8
000000000000013e 0000000000000001 MS 0 0 1
[33] .debug_rnglists PROGBITS 0000000000000000 00003fe6
0000000000000042 0000000000000000 0 0 1
[34] .symtab SYMTAB 0000000000000000 00004028
00000000000003a8 0000000000000018 35 20 8
[35] .strtab STRTAB 0000000000000000 000043d0
00000000000001f7 0000000000000000 0 0 1
[36] .shstrtab STRTAB 0000000000000000 000045c7
0000000000000176 0000000000000000 0 0 1
Key to Flags:
W (write), A (alloc), X (execute), M (merge), S (strings), I (info),
L (link order), O (extra OS processing required), G (group), T (TLS),
C (compressed), x (unknown), o (OS specific), E (exclude),
D (mbind), l (large), p (processor specific)
There are no section groups in this file.
Program Headers:
Type Offset VirtAddr PhysAddr
FileSiz MemSiz Flags Align
PHDR 0x0000000000000040 0x0000000000000040 0x0000000000000040
0x00000000000002d8 0x00000000000002d8 R 0x8
INTERP 0x0000000000000318 0x0000000000000318 0x0000000000000318
0x000000000000001c 0x000000000000001c R 0x1
[Requesting program interpreter: /lib64/ld-linux-x86-64.so.2]
LOAD 0x0000000000000000 0x0000000000000000 0x0000000000000000
0x0000000000000630 0x0000000000000630 R 0x1000
LOAD 0x0000000000001000 0x0000000000001000 0x0000000000001000
0x0000000000000171 0x0000000000000171 R E 0x1000
LOAD 0x0000000000002000 0x0000000000002000 0x0000000000002000
0x00000000000000e4 0x00000000000000e4 R 0x1000
LOAD 0x0000000000002de8 0x0000000000003de8 0x0000000000003de8
0x0000000000000248 0x0000000000000250 RW 0x1000
DYNAMIC 0x0000000000002df8 0x0000000000003df8 0x0000000000003df8
0x00000000000001e0 0x00000000000001e0 RW 0x8
NOTE 0x0000000000000338 0x0000000000000338 0x0000000000000338
0x0000000000000040 0x0000000000000040 R 0x8
NOTE 0x0000000000000378 0x0000000000000378 0x0000000000000378
0x0000000000000044 0x0000000000000044 R 0x4
GNU_PROPERTY 0x0000000000000338 0x0000000000000338 0x0000000000000338
0x0000000000000040 0x0000000000000040 R 0x8
GNU_EH_FRAME 0x000000000000201c 0x000000000000201c 0x000000000000201c
0x000000000000002c 0x000000000000002c R 0x4
GNU_STACK 0x0000000000000000 0x0000000000000000 0x0000000000000000
0x0000000000000000 0x0000000000000000 RW 0x10
GNU_RELRO 0x0000000000002de8 0x0000000000003de8 0x0000000000003de8
0x0000000000000218 0x0000000000000218 R 0x1
Section to Segment mapping:
Segment Sections...
00
01 .interp
02 .interp .note.gnu.property .note.gnu.build-id .note.ABI-tag .gnu.hash .dynsym .dynstr .gnu.version .gnu.version_r .rela.dyn .rela.plt
03 .init .plt .text .fini
04 .rodata .eh_frame_hdr .eh_frame
05 .init_array .fini_array .dynamic .got .got.plt .data .bss
06 .dynamic
07 .note.gnu.property
08 .note.gnu.build-id .note.ABI-tag
09 .note.gnu.property
10 .eh_frame_hdr
11
12 .init_array .fini_array .dynamic .got
Dynamic section at offset 0x2df8 contains 26 entries:
Tag Type Name/Value
0x0000000000000001 (NEEDED) Shared library: [libc.so.6]
0x000000000000000c (INIT) 0x1000
0x000000000000000d (FINI) 0x1164
0x0000000000000019 (INIT_ARRAY) 0x3de8
0x000000000000001b (INIT_ARRAYSZ) 8 (bytes)
0x000000000000001a (FINI_ARRAY) 0x3df0
0x000000000000001c (FINI_ARRAYSZ) 8 (bytes)
0x000000006ffffef5 (GNU_HASH) 0x3c0
0x0000000000000005 (STRTAB) 0x488
0x0000000000000006 (SYMTAB) 0x3e0
0x000000000000000a (STRSZ) 141 (bytes)
0x000000000000000b (SYMENT) 24 (bytes)
0x0000000000000015 (DEBUG) 0x0
0x0000000000000003 (PLTGOT) 0x4000
0x0000000000000002 (PLTRELSZ) 24 (bytes)
0x0000000000000014 (PLTREL) RELA
0x0000000000000017 (JMPREL) 0x618
0x0000000000000007 (RELA) 0x558
0x0000000000000008 (RELASZ) 192 (bytes)
0x0000000000000009 (RELAENT) 24 (bytes)
0x000000006ffffffb (FLAGS_1) Flags: PIE
0x000000006ffffffe (VERNEED) 0x528
0x000000006fffffff (VERNEEDNUM) 1
0x000000006ffffff0 (VERSYM) 0x516
0x000000006ffffff9 (RELACOUNT) 3
0x0000000000000000 (NULL) 0x0
Relocation section '.rela.dyn' at offset 0x558 contains 8 entries:
Offset Info Type Sym. Value Sym. Name + Addend
000000003de8 000000000008 R_X86_64_RELATIVE 1130
000000003df0 000000000008 R_X86_64_RELATIVE 10e0
000000004028 000000000008 R_X86_64_RELATIVE 4028
000000003fd8 000100000006 R_X86_64_GLOB_DAT 0000000000000000 __libc_start_main@GLIBC_2.34 + 0
000000003fe0 000200000006 R_X86_64_GLOB_DAT 0000000000000000 _ITM_deregisterTM[...] + 0
000000003fe8 000400000006 R_X86_64_GLOB_DAT 0000000000000000 __gmon_start__ + 0
000000003ff0 000500000006 R_X86_64_GLOB_DAT 0000000000000000 _ITM_registerTMCl[...] + 0
000000003ff8 000600000006 R_X86_64_GLOB_DAT 0000000000000000 __cxa_finalize@GLIBC_2.2.5 + 0
Relocation section '.rela.plt' at offset 0x618 contains 1 entry:
Offset Info Type Sym. Value Sym. Name + Addend
000000004018 000300000007 R_X86_64_JUMP_SLO 0000000000000000 puts@GLIBC_2.2.5 + 0
No processor specific unwind information to decode
Symbol table '.dynsym' contains 7 entries:
Num: Value Size Type Bind Vis Ndx Name
0: 0000000000000000 0 NOTYPE LOCAL DEFAULT UND
1: 0000000000000000 0 FUNC GLOBAL DEFAULT UND _[...]@GLIBC_2.34 (2)
2: 0000000000000000 0 NOTYPE WEAK DEFAULT UND _ITM_deregisterT[...]
3: 0000000000000000 0 FUNC GLOBAL DEFAULT UND puts@GLIBC_2.2.5 (3)
4: 0000000000000000 0 NOTYPE WEAK DEFAULT UND __gmon_start__
5: 0000000000000000 0 NOTYPE WEAK DEFAULT UND _ITM_registerTMC[...]
6: 0000000000000000 0 FUNC WEAK DEFAULT UND [...]@GLIBC_2.2.5 (3)
Symbol table '.symtab' contains 39 entries:
Num: Value Size Type Bind Vis Ndx Name
0: 0000000000000000 0 NOTYPE LOCAL DEFAULT UND
1: 0000000000000000 0 FILE LOCAL DEFAULT ABS abi-note.c
2: 000000000000039c 32 OBJECT LOCAL DEFAULT 4 __abi_tag
3: 0000000000000000 0 FILE LOCAL DEFAULT ABS init.c
4: 0000000000000000 0 FILE LOCAL DEFAULT ABS crtstuff.c
5: 0000000000001070 0 FUNC LOCAL DEFAULT 14 deregister_tm_clones
6: 00000000000010a0 0 FUNC LOCAL DEFAULT 14 register_tm_clones
7: 00000000000010e0 0 FUNC LOCAL DEFAULT 14 __do_global_dtors_aux
8: 0000000000004030 1 OBJECT LOCAL DEFAULT 25 completed.0
9: 0000000000003df0 0 OBJECT LOCAL DEFAULT 20 __do_global_dtor[...]
10: 0000000000001130 0 FUNC LOCAL DEFAULT 14 frame_dummy
11: 0000000000003de8 0 OBJECT LOCAL DEFAULT 19 __frame_dummy_in[...]
12: 0000000000000000 0 FILE LOCAL DEFAULT ABS main.c
13: 0000000000000000 0 FILE LOCAL DEFAULT ABS example.c
14: 0000000000000000 0 FILE LOCAL DEFAULT ABS crtstuff.c
15: 00000000000020e0 0 OBJECT LOCAL DEFAULT 18 __FRAME_END__
16: 0000000000000000 0 FILE LOCAL DEFAULT ABS
17: 0000000000003df8 0 OBJECT LOCAL DEFAULT 21 _DYNAMIC
18: 000000000000201c 0 NOTYPE LOCAL DEFAULT 17 __GNU_EH_FRAME_HDR
19: 0000000000004000 0 OBJECT LOCAL DEFAULT 23 _GLOBAL_OFFSET_TABLE_
20: 0000000000000000 0 FUNC GLOBAL DEFAULT UND __libc_start_mai[...]
21: 0000000000000000 0 NOTYPE WEAK DEFAULT UND _ITM_deregisterT[...]
22: 0000000000004020 0 NOTYPE WEAK DEFAULT 24 data_start
23: 000000000000114e 22 FUNC GLOBAL DEFAULT 14 printRef
24: 0000000000000000 0 FUNC GLOBAL DEFAULT UND puts@GLIBC_2.2.5
25: 0000000000004030 0 NOTYPE GLOBAL DEFAULT 24 _edata
26: 0000000000001164 0 FUNC GLOBAL HIDDEN 15 _fini
27: 0000000000004020 0 NOTYPE GLOBAL DEFAULT 24 __data_start
28: 0000000000000000 0 NOTYPE WEAK DEFAULT UND __gmon_start__
29: 0000000000004028 0 OBJECT GLOBAL HIDDEN 24 __dso_handle
30: 0000000000002000 4 OBJECT GLOBAL DEFAULT 16 _IO_stdin_used
31: 0000000000004038 0 NOTYPE GLOBAL DEFAULT 25 _end
32: 0000000000001040 38 FUNC GLOBAL DEFAULT 14 _start
33: 0000000000004030 0 NOTYPE GLOBAL DEFAULT 25 __bss_start
34: 0000000000001139 21 FUNC GLOBAL DEFAULT 14 main
35: 0000000000004030 0 OBJECT GLOBAL HIDDEN 24 __TMC_END__
36: 0000000000000000 0 NOTYPE WEAK DEFAULT UND _ITM_registerTMC[...]
37: 0000000000000000 0 FUNC WEAK DEFAULT UND __cxa_finalize@G[...]
38: 0000000000001000 0 FUNC GLOBAL HIDDEN 12 _init
Version symbols section '.gnu.version' contains 7 entries:
Addr: 0x0000000000000516 Offset: 0x000516 Link: 6 (.dynsym)
000: 0 (*local*) 2 (GLIBC_2.34) 1 (*global*) 3 (GLIBC_2.2.5)
004: 1 (*global*) 1 (*global*) 3 (GLIBC_2.2.5)
Version needs section '.gnu.version_r' contains 1 entry:
Addr: 0x0000000000000528 Offset: 0x000528 Link: 7 (.dynstr)
000000: Version: 1 File: libc.so.6 Cnt: 2
0x0010: Name: GLIBC_2.2.5 Flags: none Version: 3
0x0020: Name: GLIBC_2.34 Flags: none Version: 2
Displaying notes found in: .note.gnu.property
Owner Data size Description
GNU 0x00000030 NT_GNU_PROPERTY_TYPE_0
Properties: x86 ISA needed: x86-64-baseline
x86 feature used: x86
x86 ISA used:
Displaying notes found in: .note.gnu.build-id
Owner Data size Description
GNU 0x00000014 NT_GNU_BUILD_ID (unique build ID bitstring)
Build ID: 37fa5a5311ba7bfb5f69bdd5ecf83814345f3cf1
Displaying notes found in: .note.ABI-tag
Owner Data size Description
GNU 0x00000010 NT_GNU_ABI_TAG (ABI version tag)
OS: Linux, ABI: 4.4.0
In the Executable file, we too have ELF Header at the top, next Section is the Program Headers.
- CODE -> .code .rodata -> Read and execute
- DATA -> .data .bss -> Read and write
- STACK -> created at runtime -> Read and write
- HEAP -> created at runtime -> Read and write