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

   1 /* Copyright (C) 1996-2014 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3    Contributed by David Mosberger <davidm@azstarnet.com>, 1996.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library.  If not, see
  17    <http://www.gnu.org/licenses/>.  */
  18
  19 #include <sysdep.h>
  20
  21 /*
  22  * This is for COMPATIBILITY with Linux/x86 only.  Linux/Alpha system
  23  * calls return an error indication in a3.  This allows arbitrary 64bit
  24  * values to be returned in v0 (because negative values are not
  25  * mistaken as error numbers).  However, C allows only one value to
  26  * be returned, so the interface below folds the error indication passed in
  27  * a3 back into v0: it sets v0 to -errno if an error occurs.  Thus,
  28  * no negative 64bit numbers can be returned.  To avoid this problem,
  29  * use assembly stubs wherever possible/convenient.
  30  *
  31  * Usage:
  32  *
  33  * long syscall(syscall_number, arg1, arg2, arg3, arg4, arg5, arg6)
  34  *
  35  * syscall_number = the index of the system call we're invoking
  36  * arg1-arg6 = up to 6 integer arguments to the system call
  37  *
  38  * We need to do some arg shifting: the kernel expects the
  39  * syscall number in v0 and the first six args in a0-a5.
  40  *
  41  */
  42
  43
  44 LEAF(__syscall, 0)
  45 #ifdef PROF
  46         ldgp    gp, 0(pv)
  47         .set noat
  48         lda     AT, _mcount
  49         jsr     AT, (AT), _mcount
  50         .set at
  51         .prologue 1
  52 #else
  53         .prologue 0
  54 #endif
  55
  56         mov     a0, v0          /* Syscall number -> v0 */
  57         mov     a1, a0          /* arg1-arg5 -> a0-a4 */
  58         mov     a2, a1
  59         mov     a3, a2
  60         mov     a4, a3
  61         mov     a5, a4
  62         ldq     a5,0(sp)        /* arg6 -> a5 */
  63
  64         call_pal PAL_callsys    /* Invoke system call */
  65         bne     a3, SYSCALL_ERROR_LABEL
  66         ret
  67
  68 PSEUDO_END(__syscall)
  69
  70 weak_alias (__syscall, syscall)