El ensamblador en línea para la función de envoltura no funciona por alguna razón
Estoy intentando escribir una función de envoltorio para la llamada al sistema read (), usando asm volatile, pero no funcionará, ya que la resolución no cambia su valor.
Aquí está el código:
<code>ssize_t my_read(int fd, void *buf, size_t count)
{
ssize_t res;
__asm__ volatile(
"int $0x80" /* make the request to the OS */
: "=a" (res), /* return result in eax ("a") */
"+b" (fd), /* pass arg1 in ebx ("b") */
"+c" (buf), /* pass arg2 in ecx ("c") */
"+d" (count) /* pass arg3 in edx ("d") */
: "a" (5) /* passing the system call for read to %eax , with call number 5 */
: "memory", "cc"); /* announce to the compiler that the memory and condition codes have been modified */
/* The operating system will return a negative value on error;
* wrappers return -1 on error and set the errno global variable */
if (-125 <= res && res < 0)
{
errno = -res;
res = -1;
}
return res;
}
</code>y aqui estaint main () :
<code> int main() {
int fd = 432423;
char buf[128];
size_t count = 128;
my_read(fd, buf, count);
return 0;
}
</code>Estoy haciendo algo mal ? tal vez sea por lavolatile ?
He intentado depurar el código, y cuando Eclipse entra enmy_read(fd, buf, count); y llega a la linea__asm__ volatile( enmy_read , falla y entra enif (-125 <= res && res < 0) ...
EDITAR:
<code>ssize_t my_read(int fd, void *buf, size_t count)
{
ssize_t res;
__asm__ volatile(
"int $0x80" /* make the request to the OS */
: "=a" (res) /* return result in eax ("a") */
: "a" (5) , /* passing the system call for read to %eax , with call number 5 */
"b" (fd), /* pass arg1 in ebx ("b") */
"c" (buf), /* pass arg2 in ecx ("c") */
"d" (count) /* pass arg3 in edx ("d") */
: "memory", "cc"); /* announce to the compiler that the memory and condition codes have been modified */
/* The operating system will return a negative value on error;
* wrappers return -1 on error and set the errno global variable */
if (-125 <= res && res < 0)
{
errno = -res;
res = -1;
}
return res;
}
</code>y principal:
<code> int main() {
int fd = 0;
char buf[128];
size_t count = 128;
my_read(fd, buf, count);
return 0;
}
</code>