uclibc-ng/libc/sysdeps/linux/i386/__syscall_error.c

/* Wrapper for setting errno.
 * Copyright (C) 2000-2006 Erik Andersen <andersen@uclibc.org>
 *
 * Licensed under the LGPL v2.1, see the file COPYING.LIB in this tarball.
 */

/* This routine is jumped to by all the syscall handlers, to stash
 * an error number into errno.  */

/* This version uses a lot of magic and relies heavily on x86 
 * calling convention ... The advantage is that this is the same 
 * size as the previous __syscall_error() but all the .S functions
 * need just one instruction.
 *
 * Local .S files have to set %eax to the negative errno value 
 * and then jump to this function.  The neglected return to caller 
 * and return value of -1 is taken care of here so we don't have to 
 * worry about it in the .S functions.
 *
 * We have to stash the errno from %eax in a local stack var because 
 * __set_errno will prob call a function thus clobbering %eax on us.
 */

#include <errno.h>
#include <features.h>

int attribute_hidden __syscall_error(void)
{
	register int edx asm("%edx");
	asm("mov %eax, %edx");
	asm("negl %edx");
	__set_errno(edx);
	return -1;
}