malocchio
10-12-2008, 22:03
No, non complicarti troppo la vita... :)
Siccome lavori ad un livello molto basso, se utilizzi funzioni esterne al file da assemblare dovrai solo istruire GNU as perché sappia che tu vuoi utilizzare una funzione esterna (i riferimenti verranno eventualmente risolti durante il linking), poi il resto del lavoro (gestione dello stack e simili) te lo fai da te.
Ti basta un .extern printf in testa al file:
.extern printf
.data
formato: .asciiz "Ciao!\n"
.text
.globl main
main:
pushl $formato
call printf
ret
Il tutto è un po' a memoria, perdonami i possibili errori, vista anche l'ora.
ciao ;)
Grazie mille della risposta!
Per quanto sia lungo (ho approfittato della stampante scolastica) mi sono stampato per intero il manuale di riferimento di gAS ed, essendo un back-end per GCC, non dà troppa importanza a codice un po' "strano". Quando trova un simbolo che semplicemente non ho dichiarato da nessun'altra parte lo usa come se fosse dichiarato extern.
In pratica la direttiva extern è un po' inutile, in quanto ci pensa lui.
Il mio problema è un altro. Pensavo che si potesse fare in qualche modo da gcc, ma alla fine non conviene. La fase di linking deve essere usata per "vedere" le funzioni della libreria standard.
Ho messo un po' le mani nella pasta ed ho spiato il comportamento di GCC:
Ho scritto un programma molto semplice in C:
#include <stdio.h>
#include <stdlib.h>
int main () {
char *ptr;
ptr = malloc(10);
*ptr = 122;
printf("%d",*ptr);
return 0;
}
Da terminale ho dato:
gcc main.c -o main -v --save-temps
Con "-v" vedo i comandi singoli eseguiti per compilare
Con "--save-temps" vedo tutti passaggi intermedi
Il primo passaggio è dato dal file main.i:
# 1 "main.c"
# 1 "<built-in>"
# 1 "<command-line>"
# 1 "main.c"
# 1 "/usr/include/stdio.h" 1 3 4
# 28 "/usr/include/stdio.h" 3 4
# 1 "/usr/include/features.h" 1 3 4
# 330 "/usr/include/features.h" 3 4
# 1 "/usr/include/sys/cdefs.h" 1 3 4
# 348 "/usr/include/sys/cdefs.h" 3 4
# 1 "/usr/include/bits/wordsize.h" 1 3 4
# 349 "/usr/include/sys/cdefs.h" 2 3 4
# 331 "/usr/include/features.h" 2 3 4
# 354 "/usr/include/features.h" 3 4
# 1 "/usr/include/gnu/stubs.h" 1 3 4
# 1 "/usr/include/bits/wordsize.h" 1 3 4
# 5 "/usr/include/gnu/stubs.h" 2 3 4
# 1 "/usr/include/gnu/stubs-32.h" 1 3 4
# 8 "/usr/include/gnu/stubs.h" 2 3 4
# 355 "/usr/include/features.h" 2 3 4
# 29 "/usr/include/stdio.h" 2 3 4
# 1 "/usr/lib/gcc/i486-linux-gnu/4.2.4/include/stddef.h" 1 3 4
# 214 "/usr/lib/gcc/i486-linux-gnu/4.2.4/include/stddef.h" 3 4
typedef unsigned int size_t;
# 35 "/usr/include/stdio.h" 2 3 4
# 1 "/usr/include/bits/types.h" 1 3 4
# 28 "/usr/include/bits/types.h" 3 4
# 1 "/usr/include/bits/wordsize.h" 1 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;
__extension__ typedef signed long long int __int64_t;
__extension__ typedef unsigned long long int __uint64_t;
__extension__ typedef long long int __quad_t;
__extension__ typedef unsigned long long int __u_quad_t;
# 131 "/usr/include/bits/types.h" 3 4
# 1 "/usr/include/bits/typesizes.h" 1 3 4
# 132 "/usr/include/bits/types.h" 2 3 4
__extension__ typedef __u_quad_t __dev_t;
__extension__ typedef unsigned int __uid_t;
__extension__ typedef unsigned int __gid_t;
__extension__ typedef unsigned long int __ino_t;
__extension__ typedef __u_quad_t __ino64_t;
__extension__ typedef unsigned int __mode_t;
__extension__ typedef unsigned int __nlink_t;
__extension__ typedef long int __off_t;
__extension__ typedef __quad_t __off64_t;
__extension__ typedef int __pid_t;
__extension__ typedef struct { int __val[2]; } __fsid_t;
__extension__ typedef long int __clock_t;
__extension__ typedef unsigned long int __rlim_t;
__extension__ typedef __u_quad_t __rlim64_t;
__extension__ typedef unsigned int __id_t;
__extension__ typedef long int __time_t;
__extension__ typedef unsigned int __useconds_t;
__extension__ typedef long int __suseconds_t;
__extension__ typedef int __daddr_t;
__extension__ typedef long int __swblk_t;
__extension__ typedef int __key_t;
__extension__ typedef int __clockid_t;
__extension__ typedef void * __timer_t;
__extension__ typedef long int __blksize_t;
__extension__ typedef long int __blkcnt_t;
__extension__ typedef __quad_t __blkcnt64_t;
__extension__ typedef unsigned long int __fsblkcnt_t;
__extension__ typedef __u_quad_t __fsblkcnt64_t;
__extension__ typedef unsigned long int __fsfilcnt_t;
__extension__ typedef __u_quad_t __fsfilcnt64_t;
__extension__ typedef int __ssize_t;
typedef __off64_t __loff_t;
typedef __quad_t *__qaddr_t;
typedef char *__caddr_t;
__extension__ typedef int __intptr_t;
__extension__ typedef unsigned int __socklen_t;
# 37 "/usr/include/stdio.h" 2 3 4
# 45 "/usr/include/stdio.h" 3 4
struct _IO_FILE;
typedef struct _IO_FILE FILE;
# 65 "/usr/include/stdio.h" 3 4
typedef struct _IO_FILE __FILE;
# 75 "/usr/include/stdio.h" 3 4
# 1 "/usr/include/libio.h" 1 3 4
# 32 "/usr/include/libio.h" 3 4
# 1 "/usr/include/_G_config.h" 1 3 4
# 15 "/usr/include/_G_config.h" 3 4
# 1 "/usr/lib/gcc/i486-linux-gnu/4.2.4/include/stddef.h" 1 3 4
# 16 "/usr/include/_G_config.h" 2 3 4
# 1 "/usr/include/wchar.h" 1 3 4
# 78 "/usr/include/wchar.h" 3 4
typedef struct
{
int __count;
union
{
unsigned int __wch;
char __wchb[4];
} __value;
} __mbstate_t;
# 21 "/usr/include/_G_config.h" 2 3 4
typedef struct
{
__off_t __pos;
__mbstate_t __state;
} _G_fpos_t;
typedef struct
{
__off64_t __pos;
__mbstate_t __state;
} _G_fpos64_t;
# 53 "/usr/include/_G_config.h" 3 4
typedef int _G_int16_t __attribute__ ((__mode__ (__HI__)));
typedef int _G_int32_t __attribute__ ((__mode__ (__SI__)));
typedef unsigned int _G_uint16_t __attribute__ ((__mode__ (__HI__)));
typedef unsigned int _G_uint32_t __attribute__ ((__mode__ (__SI__)));
# 33 "/usr/include/libio.h" 2 3 4
# 53 "/usr/include/libio.h" 3 4
# 1 "/usr/lib/gcc/i486-linux-gnu/4.2.4/include/stdarg.h" 1 3 4
# 43 "/usr/lib/gcc/i486-linux-gnu/4.2.4/include/stdarg.h" 3 4
typedef __builtin_va_list __gnuc_va_list;
# 54 "/usr/include/libio.h" 2 3 4
# 170 "/usr/include/libio.h" 3 4
struct _IO_jump_t; struct _IO_FILE;
# 180 "/usr/include/libio.h" 3 4
typedef void _IO_lock_t;
struct _IO_marker {
struct _IO_marker *_next;
struct _IO_FILE *_sbuf;
int _pos;
# 203 "/usr/include/libio.h" 3 4
};
enum __codecvt_result
{
__codecvt_ok,
__codecvt_partial,
__codecvt_error,
__codecvt_noconv
};
# 271 "/usr/include/libio.h" 3 4
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;
# 319 "/usr/include/libio.h" 3 4
__off64_t _offset;
# 328 "/usr/include/libio.h" 3 4
void *__pad1;
void *__pad2;
void *__pad3;
void *__pad4;
size_t __pad5;
int _mode;
char _unused2[15 * sizeof (int) - 4 * sizeof (void *) - sizeof (size_t)];
};
typedef struct _IO_FILE _IO_FILE;
struct _IO_FILE_plus;
extern struct _IO_FILE_plus _IO_2_1_stdin_;
extern struct _IO_FILE_plus _IO_2_1_stdout_;
extern struct _IO_FILE_plus _IO_2_1_stderr_;
# 364 "/usr/include/libio.h" 3 4
typedef __ssize_t __io_read_fn (void *__cookie, char *__buf, size_t __nbytes);
typedef __ssize_t __io_write_fn (void *__cookie, __const char *__buf,
size_t __n);
typedef int __io_seek_fn (void *__cookie, __off64_t *__pos, int __w);
typedef int __io_close_fn (void *__cookie);
# 416 "/usr/include/libio.h" 3 4
extern int __underflow (_IO_FILE *);
extern int __uflow (_IO_FILE *);
extern int __overflow (_IO_FILE *, int);
# 458 "/usr/include/libio.h" 3 4
extern int _IO_getc (_IO_FILE *__fp);
extern int _IO_putc (int __c, _IO_FILE *__fp);
extern int _IO_feof (_IO_FILE *__fp) __attribute__ ((__nothrow__));
extern int _IO_ferror (_IO_FILE *__fp) __attribute__ ((__nothrow__));
extern int _IO_peekc_locked (_IO_FILE *__fp);
extern void _IO_flockfile (_IO_FILE *) __attribute__ ((__nothrow__));
extern void _IO_funlockfile (_IO_FILE *) __attribute__ ((__nothrow__));
extern int _IO_ftrylockfile (_IO_FILE *) __attribute__ ((__nothrow__));
# 488 "/usr/include/libio.h" 3 4
extern int _IO_vfscanf (_IO_FILE * __restrict, const char * __restrict,
__gnuc_va_list, int *__restrict);
extern int _IO_vfprintf (_IO_FILE *__restrict, const char *__restrict,
__gnuc_va_list);
extern __ssize_t _IO_padn (_IO_FILE *, int, __ssize_t);
extern size_t _IO_sgetn (_IO_FILE *, void *, size_t);
extern __off64_t _IO_seekoff (_IO_FILE *, __off64_t, int, int);
extern __off64_t _IO_seekpos (_IO_FILE *, __off64_t, int);
extern void _IO_free_backup_area (_IO_FILE *) __attribute__ ((__nothrow__));
# 76 "/usr/include/stdio.h" 2 3 4
# 89 "/usr/include/stdio.h" 3 4
typedef _G_fpos_t fpos_t;
# 141 "/usr/include/stdio.h" 3 4
# 1 "/usr/include/bits/stdio_lim.h" 1 3 4
# 142 "/usr/include/stdio.h" 2 3 4
extern struct _IO_FILE *stdin;
extern struct _IO_FILE *stdout;
extern struct _IO_FILE *stderr;
extern int remove (__const char *__filename) __attribute__ ((__nothrow__));
extern int rename (__const char *__old, __const char *__new) __attribute__ ((__nothrow__));
extern FILE *tmpfile (void) ;
# 186 "/usr/include/stdio.h" 3 4
extern char *tmpnam (char *__s) __attribute__ ((__nothrow__)) ;
extern char *tmpnam_r (char *__s) __attribute__ ((__nothrow__)) ;
# 204 "/usr/include/stdio.h" 3 4
extern char *tempnam (__const char *__dir, __const char *__pfx)
__attribute__ ((__nothrow__)) __attribute__ ((__malloc__)) ;
extern int fclose (FILE *__stream);
extern int fflush (FILE *__stream);
# 229 "/usr/include/stdio.h" 3 4
extern int fflush_unlocked (FILE *__stream);
# 243 "/usr/include/stdio.h" 3 4
extern FILE *fopen (__const char *__restrict __filename,
__const char *__restrict __modes) ;
extern FILE *freopen (__const char *__restrict __filename,
__const char *__restrict __modes,
FILE *__restrict __stream) ;
# 272 "/usr/include/stdio.h" 3 4
# 283 "/usr/include/stdio.h" 3 4
extern FILE *fdopen (int __fd, __const char *__modes) __attribute__ ((__nothrow__)) ;
# 304 "/usr/include/stdio.h" 3 4
extern void setbuf (FILE *__restrict __stream, char *__restrict __buf) __attribute__ ((__nothrow__));
extern int setvbuf (FILE *__restrict __stream, char *__restrict __buf,
int __modes, size_t __n) __attribute__ ((__nothrow__));
extern void setbuffer (FILE *__restrict __stream, char *__restrict __buf,
size_t __size) __attribute__ ((__nothrow__));
extern void setlinebuf (FILE *__stream) __attribute__ ((__nothrow__));
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)));
# 398 "/usr/include/stdio.h" 3 4
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__));
# 441 "/usr/include/stdio.h" 3 4
# 504 "/usr/include/stdio.h" 3 4
extern int fgetc (FILE *__stream);
extern int getc (FILE *__stream);
extern int getchar (void);
# 528 "/usr/include/stdio.h" 3 4
extern int getc_unlocked (FILE *__stream);
extern int getchar_unlocked (void);
# 539 "/usr/include/stdio.h" 3 4
extern int fgetc_unlocked (FILE *__stream);
extern int fputc (int __c, FILE *__stream);
extern int putc (int __c, FILE *__stream);
extern int putchar (int __c);
# 572 "/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)
;
extern char *gets (char *__s) ;
# 653 "/usr/include/stdio.h" 3 4
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) ;
# 706 "/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);
# 742 "/usr/include/stdio.h" 3 4
extern int fseeko (FILE *__stream, __off_t __off, int __whence);
extern __off_t ftello (FILE *__stream) ;
# 761 "/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);
# 784 "/usr/include/stdio.h" 3 4
# 793 "/usr/include/stdio.h" 3 4
extern void clearerr (FILE *__stream) __attribute__ ((__nothrow__));
extern int feof (FILE *__stream) __attribute__ ((__nothrow__)) ;
extern int ferror (FILE *__stream) __attribute__ ((__nothrow__)) ;
extern void clearerr_unlocked (FILE *__stream) __attribute__ ((__nothrow__));
extern int feof_unlocked (FILE *__stream) __attribute__ ((__nothrow__)) ;
extern int ferror_unlocked (FILE *__stream) __attribute__ ((__nothrow__)) ;
extern void perror (__const char *__s);
# 1 "/usr/include/bits/sys_errlist.h" 1 3 4
# 27 "/usr/include/bits/sys_errlist.h" 3 4
extern int sys_nerr;
extern __const char *__const sys_errlist[];
# 823 "/usr/include/stdio.h" 2 3 4
extern int fileno (FILE *__stream) __attribute__ ((__nothrow__)) ;
extern int fileno_unlocked (FILE *__stream) __attribute__ ((__nothrow__)) ;
# 842 "/usr/include/stdio.h" 3 4
extern FILE *popen (__const char *__command, __const char *__modes) ;
extern int pclose (FILE *__stream);
extern char *ctermid (char *__s) __attribute__ ((__nothrow__));
# 882 "/usr/include/stdio.h" 3 4
extern void flockfile (FILE *__stream) __attribute__ ((__nothrow__));
extern int ftrylockfile (FILE *__stream) __attribute__ ((__nothrow__)) ;
extern void funlockfile (FILE *__stream) __attribute__ ((__nothrow__));
# 912 "/usr/include/stdio.h" 3 4
# 2 "main.c" 2
# 1 "/usr/include/stdlib.h" 1 3 4
# 33 "/usr/include/stdlib.h" 3 4
# 1 "/usr/lib/gcc/i486-linux-gnu/4.2.4/include/stddef.h" 1 3 4
# 326 "/usr/lib/gcc/i486-linux-gnu/4.2.4/include/stddef.h" 3 4
typedef int wchar_t;
# 34 "/usr/include/stdlib.h" 2 3 4
# 96 "/usr/include/stdlib.h" 3 4
typedef struct
{
int quot;
int rem;
} div_t;
typedef struct
{
long int quot;
long int rem;
} ldiv_t;
# 140 "/usr/include/stdlib.h" 3 4
extern size_t __ctype_get_mb_cur_max (void) __attribute__ ((__nothrow__)) ;
extern double atof (__const char *__nptr)
__attribute__ ((__nothrow__)) __attribute__ ((__pure__)) __attribute__ ((__nonnull__ (1))) ;
extern int atoi (__const char *__nptr)
__attribute__ ((__nothrow__)) __attribute__ ((__pure__)) __attribute__ ((__nonnull__ (1))) ;
extern long int atol (__const char *__nptr)
__attribute__ ((__nothrow__)) __attribute__ ((__pure__)) __attribute__ ((__nonnull__ (1))) ;
__extension__ extern long long int atoll (__const char *__nptr)
__attribute__ ((__nothrow__)) __attribute__ ((__pure__)) __attribute__ ((__nonnull__ (1))) ;
extern double strtod (__const char *__restrict __nptr,
char **__restrict __endptr)
__attribute__ ((__nothrow__)) __attribute__ ((__nonnull__ (1))) ;
# 182 "/usr/include/stdlib.h" 3 4
extern long int strtol (__const char *__restrict __nptr,
char **__restrict __endptr, int __base)
__attribute__ ((__nothrow__)) __attribute__ ((__nonnull__ (1))) ;
extern unsigned long int strtoul (__const char *__restrict __nptr,
char **__restrict __endptr, int __base)
__attribute__ ((__nothrow__)) __attribute__ ((__nonnull__ (1))) ;
__extension__
extern long long int strtoq (__const char *__restrict __nptr,
char **__restrict __endptr, int __base)
__attribute__ ((__nothrow__)) __attribute__ ((__nonnull__ (1))) ;
__extension__
extern unsigned long long int strtouq (__const char *__restrict __nptr,
char **__restrict __endptr, int __base)
__attribute__ ((__nothrow__)) __attribute__ ((__nonnull__ (1))) ;
__extension__
extern long long int strtoll (__const char *__restrict __nptr,
char **__restrict __endptr, int __base)
__attribute__ ((__nothrow__)) __attribute__ ((__nonnull__ (1))) ;
__extension__
extern unsigned long long int strtoull (__const char *__restrict __nptr,
char **__restrict __endptr, int __base)
__attribute__ ((__nothrow__)) __attribute__ ((__nonnull__ (1))) ;
# 311 "/usr/include/stdlib.h" 3 4
extern char *l64a (long int __n) __attribute__ ((__nothrow__)) ;
extern long int a64l (__const char *__s)
__attribute__ ((__nothrow__)) __attribute__ ((__pure__)) __attribute__ ((__nonnull__ (1))) ;
# 1 "/usr/include/sys/types.h" 1 3 4
# 29 "/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;
# 62 "/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;
typedef __off_t off_t;
# 100 "/usr/include/sys/types.h" 3 4
typedef __pid_t pid_t;
typedef __id_t id_t;
typedef __ssize_t ssize_t;
typedef __daddr_t daddr_t;
typedef __caddr_t caddr_t;
typedef __key_t key_t;
# 133 "/usr/include/sys/types.h" 3 4
# 1 "/usr/include/time.h" 1 3 4
# 75 "/usr/include/time.h" 3 4
typedef __time_t time_t;
# 93 "/usr/include/time.h" 3 4
typedef __clockid_t clockid_t;
# 105 "/usr/include/time.h" 3 4
typedef __timer_t timer_t;
# 134 "/usr/include/sys/types.h" 2 3 4
# 147 "/usr/include/sys/types.h" 3 4
# 1 "/usr/lib/gcc/i486-linux-gnu/4.2.4/include/stddef.h" 1 3 4
# 148 "/usr/include/sys/types.h" 2 3 4
typedef unsigned long int ulong;
typedef unsigned short int ushort;
typedef unsigned int uint;
# 195 "/usr/include/sys/types.h" 3 4
typedef int int8_t __attribute__ ((__mode__ (__QI__)));
typedef int int16_t __attribute__ ((__mode__ (__HI__)));
typedef int int32_t __attribute__ ((__mode__ (__SI__)));
typedef int int64_t __attribute__ ((__mode__ (__DI__)));
typedef unsigned int u_int8_t __attribute__ ((__mode__ (__QI__)));
typedef unsigned int u_int16_t __attribute__ ((__mode__ (__HI__)));
typedef unsigned int u_int32_t __attribute__ ((__mode__ (__SI__)));
typedef unsigned int u_int64_t __attribute__ ((__mode__ (__DI__)));
typedef int register_t __attribute__ ((__mode__ (__word__)));
# 217 "/usr/include/sys/types.h" 3 4
# 1 "/usr/include/endian.h" 1 3 4
# 37 "/usr/include/endian.h" 3 4
# 1 "/usr/include/bits/endian.h" 1 3 4
# 38 "/usr/include/endian.h" 2 3 4
# 218 "/usr/include/sys/types.h" 2 3 4
# 1 "/usr/include/sys/select.h" 1 3 4
# 31 "/usr/include/sys/select.h" 3 4
# 1 "/usr/include/bits/select.h" 1 3 4
# 32 "/usr/include/sys/select.h" 2 3 4
# 1 "/usr/include/bits/sigset.h" 1 3 4
# 24 "/usr/include/bits/sigset.h" 3 4
typedef int __sig_atomic_t;
typedef struct
{
unsigned long int __val[(1024 / (8 * sizeof (unsigned long int)))];
} __sigset_t;
# 35 "/usr/include/sys/select.h" 2 3 4
typedef __sigset_t sigset_t;
# 1 "/usr/include/time.h" 1 3 4
# 121 "/usr/include/time.h" 3 4
struct timespec
{
__time_t tv_sec;
long int tv_nsec;
};
# 45 "/usr/include/sys/select.h" 2 3 4
# 1 "/usr/include/bits/time.h" 1 3 4
# 69 "/usr/include/bits/time.h" 3 4
struct timeval
{
__time_t tv_sec;
__suseconds_t tv_usec;
};
# 47 "/usr/include/sys/select.h" 2 3 4
typedef __suseconds_t suseconds_t;
typedef long int __fd_mask;
# 67 "/usr/include/sys/select.h" 3 4
typedef struct
{
__fd_mask __fds_bits[1024 / (8 * sizeof (__fd_mask))];
} fd_set;
typedef __fd_mask fd_mask;
# 99 "/usr/include/sys/select.h" 3 4
# 109 "/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);
# 121 "/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);
# 221 "/usr/include/sys/types.h" 2 3 4
# 1 "/usr/include/sys/sysmacros.h" 1 3 4
# 30 "/usr/include/sys/sysmacros.h" 3 4
__extension__
extern unsigned int gnu_dev_major (unsigned long long int __dev)
__attribute__ ((__nothrow__));
__extension__
extern unsigned int gnu_dev_minor (unsigned long long int __dev)
__attribute__ ((__nothrow__));
__extension__
extern unsigned long long int gnu_dev_makedev (unsigned int __major,
unsigned int __minor)
__attribute__ ((__nothrow__));
# 224 "/usr/include/sys/types.h" 2 3 4
# 235 "/usr/include/sys/types.h" 3 4
typedef __blkcnt_t blkcnt_t;
typedef __fsblkcnt_t fsblkcnt_t;
typedef __fsfilcnt_t fsfilcnt_t;
# 270 "/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/wordsize.h" 1 3 4
# 24 "/usr/include/bits/pthreadtypes.h" 2 3 4
# 50 "/usr/include/bits/pthreadtypes.h" 3 4
typedef unsigned long int pthread_t;
typedef union
{
char __size[36];
long int __align;
} pthread_attr_t;
# 67 "/usr/include/bits/pthreadtypes.h" 3 4
typedef struct __pthread_internal_slist
{
struct __pthread_internal_slist *__next;
} __pthread_slist_t;
typedef union
{
struct __pthread_mutex_s
{
int __lock;
unsigned int __count;
int __owner;
int __kind;
unsigned int __nusers;
__extension__ union
{
int __spins;
__pthread_slist_t __list;
};
} __data;
char __size[24];
long int __align;
} pthread_mutex_t;
typedef union
{
char __size[4];
int __align;
} pthread_mutexattr_t;
typedef union
{
struct
{
int __lock;
unsigned int __futex;
__extension__ unsigned long long int __total_seq;
__extension__ unsigned long long int __wakeup_seq;
__extension__ unsigned long long int __woken_seq;
void *__mutex;
unsigned int __nwaiters;
unsigned int __broadcast_seq;
} __data;
char __size[48];
__extension__ long long int __align;
} pthread_cond_t;
typedef union
{
char __size[4];
int __align;
} pthread_condattr_t;
typedef unsigned int pthread_key_t;
typedef int pthread_once_t;
typedef union
{
# 170 "/usr/include/bits/pthreadtypes.h" 3 4
struct
{
int __lock;
unsigned int __nr_readers;
unsigned int __readers_wakeup;
unsigned int __writer_wakeup;
unsigned int __nr_readers_queued;
unsigned int __nr_writers_queued;
unsigned char __flags;
unsigned char __shared;
unsigned char __pad1;
unsigned char __pad2;
int __writer;
} __data;
char __size[32];
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[20];
long int __align;
} pthread_barrier_t;
typedef union
{
char __size[4];
int __align;
} pthread_barrierattr_t;
# 271 "/usr/include/sys/types.h" 2 3 4
# 321 "/usr/include/stdlib.h" 2 3 4
extern long int random (void) __attribute__ ((__nothrow__));
extern void srandom (unsigned int __seed) __attribute__ ((__nothrow__));
extern char *initstate (unsigned int __seed, char *__statebuf,
size_t __statelen) __attribute__ ((__nothrow__)) __attribute__ ((__nonnull__ (2)));
extern char *setstate (char *__statebuf) __attribute__ ((__nothrow__)) __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__)) __attribute__ ((__nonnull__ (1, 2)));
extern int srandom_r (unsigned int __seed, struct random_data *__buf)
__attribute__ ((__nothrow__)) __attribute__ ((__nonnull__ (2)));
extern int initstate_r (unsigned int __seed, char *__restrict __statebuf,
size_t __statelen,
struct random_data *__restrict __buf)
__attribute__ ((__nothrow__)) __attribute__ ((__nonnull__ (2, 4)));
extern int setstate_r (char *__restrict __statebuf,
struct random_data *__restrict __buf)
__attribute__ ((__nothrow__)) __attribute__ ((__nonnull__ (1, 2)));
extern int rand (void) __attribute__ ((__nothrow__));
extern void srand (unsigned int __seed) __attribute__ ((__nothrow__));
extern int rand_r (unsigned int *__seed) __attribute__ ((__nothrow__));
extern double drand48 (void) __attribute__ ((__nothrow__));
extern double erand48 (unsigned short int __xsubi[3]) __attribute__ ((__nothrow__)) __attribute__ ((__nonnull__ (1)));
extern long int lrand48 (void) __attribute__ ((__nothrow__));
extern long int nrand48 (unsigned short int __xsubi[3])
__attribute__ ((__nothrow__)) __attribute__ ((__nonnull__ (1)));
extern long int mrand48 (void) __attribute__ ((__nothrow__));
extern long int jrand48 (unsigned short int __xsubi[3])
__attribute__ ((__nothrow__)) __attribute__ ((__nonnull__ (1)));
extern void srand48 (long int __seedval) __attribute__ ((__nothrow__));
extern unsigned short int *seed48 (unsigned short int __seed16v[3])
__attribute__ ((__nothrow__)) __attribute__ ((__nonnull__ (1)));
extern void lcong48 (unsigned short int __param[7]) __attribute__ ((__nothrow__)) __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;
unsigned long long int __a;
};
extern int drand48_r (struct drand48_data *__restrict __buffer,
double *__restrict __result) __attribute__ ((__nothrow__)) __attribute__ ((__nonnull__ (1, 2)));
extern int erand48_r (unsigned short int __xsubi[3],
struct drand48_data *__restrict __buffer,
double *__restrict __result) __attribute__ ((__nothrow__)) __attribute__ ((__nonnull__ (1, 2)));
extern int lrand48_r (struct drand48_data *__restrict __buffer,
long int *__restrict __result)
__attribute__ ((__nothrow__)) __attribute__ ((__nonnull__ (1, 2)));
extern int nrand48_r (unsigned short int __xsubi[3],
struct drand48_data *__restrict __buffer,
long int *__restrict __result)
__attribute__ ((__nothrow__)) __attribute__ ((__nonnull__ (1, 2)));
extern int mrand48_r (struct drand48_data *__restrict __buffer,
long int *__restrict __result)
__attribute__ ((__nothrow__)) __attribute__ ((__nonnull__ (1, 2)));
extern int jrand48_r (unsigned short int __xsubi[3],
struct drand48_data *__restrict __buffer,
long int *__restrict __result)
__attribute__ ((__nothrow__)) __attribute__ ((__nonnull__ (1, 2)));
extern int srand48_r (long int __seedval, struct drand48_data *__buffer)
__attribute__ ((__nothrow__)) __attribute__ ((__nonnull__ (2)));
extern int seed48_r (unsigned short int __seed16v[3],
struct drand48_data *__buffer) __attribute__ ((__nothrow__)) __attribute__ ((__nonnull__ (1, 2)));
extern int lcong48_r (unsigned short int __param[7],
struct drand48_data *__buffer)
__attribute__ ((__nothrow__)) __attribute__ ((__nonnull__ (1, 2)));
extern void *malloc (size_t __size) __attribute__ ((__nothrow__)) __attribute__ ((__malloc__)) ;
extern void *calloc (size_t __nmemb, size_t __size)
__attribute__ ((__nothrow__)) __attribute__ ((__malloc__)) ;
extern void *realloc (void *__ptr, size_t __size)
__attribute__ ((__nothrow__)) __attribute__ ((__warn_unused_result__));
extern void free (void *__ptr) __attribute__ ((__nothrow__));
extern void cfree (void *__ptr) __attribute__ ((__nothrow__));
# 1 "/usr/include/alloca.h" 1 3 4
# 25 "/usr/include/alloca.h" 3 4
# 1 "/usr/lib/gcc/i486-linux-gnu/4.2.4/include/stddef.h" 1 3 4
# 26 "/usr/include/alloca.h" 2 3 4
extern void *alloca (size_t __size) __attribute__ ((__nothrow__));
# 498 "/usr/include/stdlib.h" 2 3 4
extern void *valloc (size_t __size) __attribute__ ((__nothrow__)) __attribute__ ((__malloc__)) ;
extern int posix_memalign (void **__memptr, size_t __alignment, size_t __size)
__attribute__ ((__nothrow__)) __attribute__ ((__nonnull__ (1))) ;
extern void abort (void) __attribute__ ((__nothrow__)) __attribute__ ((__noreturn__));
extern int atexit (void (*__func) (void)) __attribute__ ((__nothrow__)) __attribute__ ((__nonnull__ (1)));
extern int on_exit (void (*__func) (int __status, void *__arg), void *__arg)
__attribute__ ((__nothrow__)) __attribute__ ((__nonnull__ (1)));
extern void exit (int __status) __attribute__ ((__nothrow__)) __attribute__ ((__noreturn__));
# 543 "/usr/include/stdlib.h" 3 4
extern char *getenv (__const char *__name) __attribute__ ((__nothrow__)) __attribute__ ((__nonnull__ (1))) ;
extern char *__secure_getenv (__const char *__name)
__attribute__ ((__nothrow__)) __attribute__ ((__nonnull__ (1))) ;
extern int putenv (char *__string) __attribute__ ((__nothrow__)) __attribute__ ((__nonnull__ (1)));
extern int setenv (__const char *__name, __const char *__value, int __replace)
__attribute__ ((__nothrow__)) __attribute__ ((__nonnull__ (2)));
extern int unsetenv (__const char *__name) __attribute__ ((__nothrow__));
extern int clearenv (void) __attribute__ ((__nothrow__));
# 583 "/usr/include/stdlib.h" 3 4
extern char *mktemp (char *__template) __attribute__ ((__nothrow__)) __attribute__ ((__nonnull__ (1))) ;
# 594 "/usr/include/stdlib.h" 3 4
extern int mkstemp (char *__template) __attribute__ ((__nonnull__ (1))) ;
# 614 "/usr/include/stdlib.h" 3 4
extern char *mkdtemp (char *__template) __attribute__ ((__nothrow__)) __attribute__ ((__nonnull__ (1))) ;
# 640 "/usr/include/stdlib.h" 3 4
extern int system (__const char *__command) ;
# 662 "/usr/include/stdlib.h" 3 4
extern char *realpath (__const char *__restrict __name,
char *__restrict __resolved) __attribute__ ((__nothrow__)) ;
typedef int (*__compar_fn_t) (__const void *, __const void *);
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)));
extern int abs (int __x) __attribute__ ((__nothrow__)) __attribute__ ((__const__)) ;
extern long int labs (long int __x) __attribute__ ((__nothrow__)) __attribute__ ((__const__)) ;
extern div_t div (int __numer, int __denom)
__attribute__ ((__nothrow__)) __attribute__ ((__const__)) ;
extern ldiv_t ldiv (long int __numer, long int __denom)
__attribute__ ((__nothrow__)) __attribute__ ((__const__)) ;
# 727 "/usr/include/stdlib.h" 3 4
extern char *ecvt (double __value, int __ndigit, int *__restrict __decpt,
int *__restrict __sign) __attribute__ ((__nothrow__)) __attribute__ ((__nonnull__ (3, 4))) ;
extern char *fcvt (double __value, int __ndigit, int *__restrict __decpt,
int *__restrict __sign) __attribute__ ((__nothrow__)) __attribute__ ((__nonnull__ (3, 4))) ;
extern char *gcvt (double __value, int __ndigit, char *__buf)
__attribute__ ((__nothrow__)) __attribute__ ((__nonnull__ (3))) ;
extern char *qecvt (long double __value, int __ndigit,
int *__restrict __decpt, int *__restrict __sign)
__attribute__ ((__nothrow__)) __attribute__ ((__nonnull__ (3, 4))) ;
extern char *qfcvt (long double __value, int __ndigit,
int *__restrict __decpt, int *__restrict __sign)
__attribute__ ((__nothrow__)) __attribute__ ((__nonnull__ (3, 4))) ;
extern char *qgcvt (long double __value, int __ndigit, char *__buf)
__attribute__ ((__nothrow__)) __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__)) __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__)) __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__)) __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__)) __attribute__ ((__nonnull__ (3, 4, 5)));
extern int mblen (__const char *__s, size_t __n) __attribute__ ((__nothrow__)) ;
extern int mbtowc (wchar_t *__restrict __pwc,
__const char *__restrict __s, size_t __n) __attribute__ ((__nothrow__)) ;
extern int wctomb (char *__s, wchar_t __wchar) __attribute__ ((__nothrow__)) ;
extern size_t mbstowcs (wchar_t *__restrict __pwcs,
__const char *__restrict __s, size_t __n) __attribute__ ((__nothrow__));
extern size_t wcstombs (char *__restrict __s,
__const wchar_t *__restrict __pwcs, size_t __n)
__attribute__ ((__nothrow__));
extern int rpmatch (__const char *__response) __attribute__ ((__nothrow__)) __attribute__ ((__nonnull__ (1))) ;
# 832 "/usr/include/stdlib.h" 3 4
extern int posix_openpt (int __oflag) ;
# 867 "/usr/include/stdlib.h" 3 4
extern int getloadavg (double __loadavg[], int __nelem)
__attribute__ ((__nothrow__)) __attribute__ ((__nonnull__ (1)));
# 883 "/usr/include/stdlib.h" 3 4
# 3 "main.c" 2
int main () {
char *ptr;
ptr = malloc(10);
*ptr = 122;
printf("%d",*ptr);
return 0;
}
(scusate la lunghezza) Il preprocessore espande gli include ricopiando i file e quindi risolvendo tutte le dipendenze. Di nessun interesse per me, perché il passaggio successivo si lascia dietro di sé tutto questo (serve solo al compilatore C, non all'assembler).
Il file main.s (codice assembler - sintassi AT&T)
.file "main.c"
.section .rodata
.LC0:
.string "%d"
.text
.globl main
.type main, @function
main:
leal 4(%esp), %ecx
andl $-16, %esp
pushl -4(%ecx)
pushl %ebp
movl %esp, %ebp
pushl %ecx
subl $36, %esp
movl $10, (%esp)
call malloc
movl %eax, -8(%ebp)
movl -8(%ebp), %eax
movb $122, (%eax)
movl -8(%ebp), %eax
movzbl (%eax), %eax
movsbl %al,%eax
movl %eax, 4(%esp)
movl $.LC0, (%esp)
call printf
movl $0, %eax
addl $36, %esp
popl %ecx
popl %ebp
leal -4(%ecx), %esp
ret
.size main, .-main
.ident "GCC: (GNU) 4.2.4 (Ubuntu 4.2.4-1ubuntu3)"
.section .note.GNU-stack,"",@progbits
Vabbè è un po' egizio il prodotto del compilatore, ma qualcosa si intravede. In grassetto ci sono le due funzioni chiamate. Da notare assolutamente che non c'è nessun altro riferimento ad esse, quindi sono dei simboli esterni (implicitamente). Se ne deduce che il lavoro lo fa il linker.
Adesso vediamo l'ouput verbose di GCC, che mi rivela tutti i passaggi compiuti:
gcc main.c -o main -v --save-temps
------------------------------------------------------------------------ ECCO LA CONFIGURAZIONE DI GCC
Using built-in specs.
Target: i486-linux-gnu
Configured with: ../src/configure -v --enable-languages=c,c++,fortran,objc,obj-c++,treelang --prefix=/usr --enable-shared --with-system-zlib --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --enable-nls --with-gxx-include-dir=/usr/include/c++/4.2 --program-suffix=-4.2 --enable-clocale=gnu --enable-libstdcxx-debug --enable-objc-gc --enable-mpfr --enable-targets=all --enable-checking=release --build=i486-linux-gnu --host=i486-linux-gnu --target=i486-linux-gnu
Thread model: posix
gcc version 4.2.4 (Ubuntu 4.2.4-1ubuntu3)
------------------------------------------------------------------------ PREPROCESSA (main.c -> main.i)
/usr/lib/gcc/i486-linux-gnu/4.2.4/cc1 -E -quiet -v main.c -mtune=generic -fpch-preprocess -o main.i
ignoring nonexistent directory "/usr/local/include/i486-linux-gnu"
ignoring nonexistent directory "/usr/lib/gcc/i486-linux-gnu/4.2.4/../../../../i486-linux-gnu/include"
ignoring nonexistent directory "/usr/include/i486-linux-gnu"
#include "..." search starts here:
#include <...> search starts here:
/usr/local/include
/usr/lib/gcc/i486-linux-gnu/4.2.4/include
/usr/include
End of search list.
----------------------------------------------------------------------------- COMPILA (main.i -> main.s)
/usr/lib/gcc/i486-linux-gnu/4.2.4/cc1 -fpreprocessed main.i -quiet -dumpbase main.c -mtune=generic -auxbase main -version -fstack-protector -fstack-protector -o main.s
GNU C version 4.2.4 (Ubuntu 4.2.4-1ubuntu3) (i486-linux-gnu)
compiled by GNU C version 4.2.4 (Ubuntu 4.2.4-1ubuntu3).
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: e2971cf2189271aeeb10133511ecea3a
------------------------------------------------------------------------------------- ASSEMBLA (main.s -> main.o)
as --traditional-format -V -Qy -o main.o main.s
GNU assembler version 2.18.0 (i486-linux-gnu) using BFD version (GNU Binutils for Ubuntu) 2.18.0.20080103
---------------------------------------------------------------------------------- LINKA (main.o -> main)
/usr/lib/gcc/i486-linux-gnu/4.2.4/collect2 --eh-frame-hdr -m elf_i386 --hash-style=both -dynamic-linker /lib/ld-linux.so.2 -o main /usr/lib/gcc/i486-linux-gnu/4.2.4/../../../../lib/crt1.o /usr/lib/gcc/i486-linux-gnu/4.2.4/../../../../lib/crti.o /usr/lib/gcc/i486-linux-gnu/4.2.4/crtbegin.o -L/usr/lib/gcc/i486-linux-gnu/4.2.4 -L/usr/lib/gcc/i486-linux-gnu/4.2.4 -L/usr/lib/gcc/i486-linux-gnu/4.2.4/../../../../lib -L/lib/../lib -L/usr/lib/../lib -L/usr/lib/gcc/i486-linux-gnu/4.2.4/../../.. main.o -lgcc --as-needed -lgcc_s --no-as-needed -lc -lgcc --as-needed -lgcc_s --no-as-needed /usr/lib/gcc/i486-linux-gnu/4.2.4/crtend.o /usr/lib/gcc/i486-linux-gnu/4.2.4/../../../../lib/crtn.o
Ho messo dei divisori per evidenziare i passaggi
Fino all'assemblaggio niente di speciale, lascia perplessi l'ultimo passaggio (LINKING).
collect2 non è altro che un alias per ld (il GNU linker). Non capisco che differenza ci sia, ma usare uno o l'altro non fa differenza.
ecco l'output di
malocchio@malocchio:~/gas$ /usr/lib/gcc/i486-linux-gnu/4.2/collect2 --help
Usage: /usr/bin/ld [options] file...
Options:
-a KEYWORD Shared library control for HP/UX compatibility
-A ARCH, --architecture ARCH
Set architecture
-b TARGET, --format TARGET Specify target for following input files
-c FILE, --mri-script FILE Read MRI format linker script
-d, -dc, -dp Force common symbols to be defined
.......
Report bugs to <http://www.sourceware.org/bugzilla/>La prima riga (in grassetto) è la più importante!
allora deduco che tutti quei percorsi ai file *.o (ovvero file oggetto già compilati ma non linkati) sono quello che fanno per me.
Allora ho fatto un mio file assembler daccapo, l'ho assemblato e l'ho linkato con ld, aggiungendo i parametri al linker con i percorsi ai file.
Primo problema: nel file assembler va usato "main" come entry point (standard C) invece che "_start" (standard per l'assembler).
Quindi:
file main.s:
.file "main.c"
.section .rodata
stringa:
.string "ciao\0"
.text
.globl main
.type main, @function
main:
pushl $stringa
call printf
addl $4, %esp
#esco
movl $1, %eax
xorl %ebx, %ebx
int $0x80
ret
Assemblo e linko, con i vari riferimenti ai file oggetto.
malocchio@malocchio:~/gas$ as main.s -o main.o
malocchio@malocchio:~/gas$ ld --eh-frame-hdr -m elf_i386 --hash-style=both -dynamic-linker /lib/ld-linux.so.2 -o main /usr/lib/gcc/i486-linux-gnu/4.2.4/../../../../lib/crt1.o /usr/lib/gcc/i486-linux-gnu/4.2.4/../../../../lib/crti.o /usr/lib/gcc/i486-linux-gnu/4.2.4/crtbegin.o -L/usr/lib/gcc/i486-linux-gnu/4.2.4 -L/usr/lib/gcc/i486-linux-gnu/4.2.4 -L/usr/lib/gcc/i486-linux-gnu/4.2.4/../../../../lib -L/lib/../lib -L/usr/lib/../lib -L/usr/lib/gcc/i486-linux-gnu/4.2.4/../../.. main.o -lgcc --as-needed -lgcc_s --no-as-needed -lc -lgcc --as-needed -lgcc_s --no-as-needed /usr/lib/gcc/i486-linux-gnu/4.2.4/crtend.o /usr/lib/gcc/i486-linux-gnu/4.2.4/../../../../lib/crtn.o
malocchio@malocchio:~/gas$ ./main
perfetto, se non fosse che non stampa niente.
Ho scoperto tramite varie prove che chiamando una "getchar()" oppure una "puts("")" dopo la printf l'ouput si vede, ed in modo corretto.
File main.s modificato:
.file "main.c"
.section .rodata
stringa:
.string "ciao\0"
.text
.globl main
.type main, @function
main:
pushl $stringa
call printf
addl $4, %esp
call getchar
#esco
movl $1, %eax
xorl %ebx, %ebx
int $0x80
ret
fase di compilazione ed execute:
malocchio@malocchio:~/gas$ as main.s -o main.o
malocchio@malocchio:~/gas$ ld --eh-frame-hdr -m elf_i386 --hash-style=both -dynamic-linker /lib/ld-linux.so.2 -o main /usr/lib/gcc/i486-linux-gnu/4.2.4/../../../../lib/crt1.o /usr/lib/gcc/i486-linux-gnu/4.2.4/../../../../lib/crti.o /usr/lib/gcc/i486-linux-gnu/4.2.4/crtbegin.o -L/usr/lib/gcc/i486-linux-gnu/4.2.4 -L/usr/lib/gcc/i486-linux-gnu/4.2.4 -L/usr/lib/gcc/i486-linux-gnu/4.2.4/../../../../lib -L/lib/../lib -L/usr/lib/../lib -L/usr/lib/gcc/i486-linux-gnu/4.2.4/../../.. main.o -lgcc --as-needed -lgcc_s --no-as-needed -lc -lgcc --as-needed -lgcc_s --no-as-needed /usr/lib/gcc/i486-linux-gnu/4.2.4/crtend.o /usr/lib/gcc/i486-linux-gnu/4.2.4/../../../../lib/crtn.o
malocchio@malocchio:~/gas$ ./main
ciao
malocchio@malocchio:~/gas$Adesso funziona!
Ecco i miei dubbi:
1) La compilazione del programma è corretta così oppure c'è un metodo più corretto??
2) Vedi il dubbio riguardo l'uso della puts() nell'assembler nel mio post precedente.
3) Perché l'ouput si visualizza solo dopo aver richiamato un'altra funzione I/O come puts o getchar?? Sembra un problema con il buffer ma non mi spiego perché.
4) Il comando per il link funziona con tutta la libreria standard oppure dovrebbe variare a seconda dei vari include che mi servirebbero se il programa fosse scritto in C?
Grazie, e scusate la lunghezza, volevo fare una cosa fatta bene.
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