glibc/sysdeps/unix/sysv/linux/alpha/syscall.S

/* Copyright (C) 1996-2024 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library.  If not, see
   <https://www.gnu.org/licenses/>.  */

#include <sysdep.h>

/*
 * This is for COMPATIBILITY with Linux/x86 only.  Linux/Alpha system
 * calls return an error indication in a3.  This allows arbitrary 64bit
 * values to be returned in v0 (because negative values are not
 * mistaken as error numbers).  However, C allows only one value to
 * be returned, so the interface below folds the error indication passed in
 * a3 back into v0: it sets v0 to -errno if an error occurs.  Thus,
 * no negative 64bit numbers can be returned.  To avoid this problem,
 * use assembly stubs wherever possible/convenient.
 *
 * Usage:
 *
 * long	syscall(syscall_number, arg1, arg2, arg3, arg4, arg5, arg6)
 *
 * syscall_number = the index of the system call we're invoking
 * arg1-arg6 = up to 6 integer arguments to the system call
 *
 * We need to do some arg shifting: the kernel expects the
 * syscall number in v0 and the first six args in a0-a5.
 *
 */


LEAF(__syscall, 0)
#ifdef PROF
	ldgp	gp, 0(pv)
	.set noat
	lda	AT, _mcount
	jsr	AT, (AT), _mcount
	.set at
	.prologue 1
#else
	.prologue 0
#endif

	mov	a0, v0		/* Syscall number -> v0 */
	mov	a1, a0		/* arg1-arg5 -> a0-a4 */
	mov	a2, a1
	mov	a3, a2
	mov	a4, a3
	mov	a5, a4
	ldq	a5,0(sp)	/* arg6 -> a5 */

	call_pal PAL_callsys	/* Invoke system call */
	bne	a3, SYSCALL_ERROR_LABEL
	ret

PSEUDO_END(__syscall)

weak_alias (__syscall, syscall)