Операционные системы -вопросы теории


Пример 3 7 Позиционнонезависимый



Пример 3.7. Позиционно-независимый код, порождаемый компилятором GNU С

/* strerror.c (emx+gcc) — Copyright (с) 1990-1996 by Eberhard Mattes */

#include <stdlib.h>
#include <string.h>
#include <emx/thread.h>

char *strerror (int errnum)
{ (
if (errnum >= 0 && errnum < _sys_nerr)
return (char *)_sys_errlist [errnum];
else
{
static char msg[] = "Unknown error ";
#if defined ( _ MT _ )
struct _thread *tp = _thread ( ) ;
#define result (tp->_th_error)
#else
static char result [32];
#endif
memcpy (result, msg, sizeof (rasg) — 1) ;
_itoa (errnum, result + sizeof (msg) — 1, 10) ;
return result;
}
}

gcc -f PIC -S strerror.c
. file "strerror"
gcc2_compiled. :
_ gnu_compiled_c :
.data
_msg.2:
.ascii "Unknown error \0"
.Icomm _result.3,32
.text
.align 2, 0x90
. globl _strerror
__strerror:
pushl %ebp
movl %esp, %ebp
pushl %ebx
call L4
L4:
popl %ebx
addl $_GLOBAL_OFFSET_TABLE_+ [ . -L4 ] , %ebx
cmpl $0,8 (%ebp)
jl L2
movl _ sys_nerr@GOT (%ebx) , %eax
movl 8 (%ebp) , %edx
cmpl %edx, (%eax)
jle L2
movl 8(%ebp),%eax
movl %eax,%edx
leal 0(,%edx,4),%eax
movl __sys_errlist@GOT(%ebx) , %edx
movl (%edx,%eax),%eax jmp LI
.align 2,0x90 jmp L3 .align 2,0x90
L2:
pushl $14
leal _msg.2@GOTOFF(%ebx),%edx
movl %edx,%eax
pushl %eax
leal _result.3@GOTOFF(%ebx) ,%edx
movl %edx,%eax
pushl %eax
call _memcpy@PLT
addl $12,%esp
pushl $10
leal _result.3@GOTOFF(%ebx) , %edx
leal 14(%edx),%eax
pushl %eax
movl 8(%ebp),%eax
pushl %eax
call __itoa@PLT
addl $12,%esp
leal _result.3@GOTOFF(%ebx) ,%edx
movl %edx,%eax
jmp LI
.align 2,0x90
L3:
LI:
movl -4 (%ebp),%ebx
leave
ret

 











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