path: root/coregrind/m_syscall.c

/*--------------------------------------------------------------------*/
/*--- Doing syscalls.                                  m_syscall.c ---*/
/*--------------------------------------------------------------------*/

/*
   This file is part of Valgrind, a dynamic binary instrumentation
   framework.

   Copyright (C) 2000-2010 Julian Seward 
      jseward@acm.org

   This program is free software; you can redistribute it and/or
   modify it under the terms of the GNU General Public License as
   published by the Free Software Foundation; either version 2 of the
   License, or (at your option) any later version.

   This program 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
   General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
   02111-1307, USA.

   The GNU General Public License is contained in the file COPYING.
*/

#include "pub_core_basics.h"
#include "pub_core_libcassert.h"
#include "pub_core_vki.h"
#include "pub_core_vkiscnums.h"
#include "pub_core_syscall.h"

/* ---------------------------------------------------------------------
   Building syscall return values.
   ------------------------------------------------------------------ */

#if defined(VGO_linux)

/* Make a SysRes value from a syscall return value.  This is
   Linux-specific.

   From:
   http://sources.redhat.com/cgi-bin/cvsweb.cgi/libc/sysdeps/unix/sysv/
   linux/i386/sysdep.h?
   rev=1.28&content-type=text/x-cvsweb-markup&cvsroot=glibc

   Linux uses a negative return value to indicate syscall errors,
   unlike most Unices, which use the condition codes' carry flag.

   Since version 2.1 the return value of a system call might be
   negative even if the call succeeded.  E.g., the 'lseek' system call
   might return a large offset.  Therefore we must not anymore test
   for < 0, but test for a real error by making sure the value in %eax
   is a real error number.  Linus said he will make sure the no
   syscall returns a value in -1 .. -4095 as a valid result so we can
   safely test with -4095.
*/

SysRes VG_(mk_SysRes_x86_linux) ( Int val ) {
   SysRes res;
   res._isError = val >= -4095 && val <= -1;
   if (res._isError) {
      res._val = (UInt)(-val);
   } else {
      res._val = (UInt)val;
   }
   return res;
}

/* Similarly .. */
SysRes VG_(mk_SysRes_amd64_linux) ( Long val ) {
   SysRes res;
   res._isError = val >= -4095 && val <= -1;
   if (res._isError) {
      res._val = (ULong)(-val);
   } else {
      res._val = (ULong)val;
   }
   return res;
}

/* PPC uses the CR7.SO bit to flag an error (CR0 in IBM-speak) */
/* Note this must be in the bottom bit of the second arg */
SysRes VG_(mk_SysRes_ppc32_linux) ( UInt val, UInt cr0so ) {
   SysRes res;
   res._isError = (cr0so & 1) != 0;
   res._val     = val;
   return res;
}

/* As per ppc32 version, cr0.so must be in l.s.b. of 2nd arg */
SysRes VG_(mk_SysRes_ppc64_linux) ( ULong val, ULong cr0so ) {
   SysRes res;
   res._isError = (cr0so & 1) != 0;
   res._val     = val;
   return res;
}

SysRes VG_(mk_SysRes_s390x_linux) ( Long val ) {
   SysRes res;
   res._isError = val >= -4095 && val <= -1;
   if (res._isError) {
      res._val = -val;
   } else {
      res._val = val;
   }
   return res;
}

SysRes VG_(mk_SysRes_arm_linux) ( Int val ) {
   SysRes res;
   res._isError = val >= -4095 && val <= -1;
   if (res._isError) {
      res._val = (UInt)(-val);
   } else {
      res._val = (UInt)val;
   }
   return res;
}

/* Generic constructors. */
SysRes VG_(mk_SysRes_Error) ( UWord err ) {
   SysRes r;
   r._isError = True;
   r._val     = err;
   return r;
}

SysRes VG_(mk_SysRes_Success) ( UWord res ) {
   SysRes r;
   r._isError = False;
   r._val     = res;
   return r;
}


#elif defined(VGO_darwin)

/* Darwin: Some syscalls return a double-word result. */
SysRes VG_(mk_SysRes_x86_darwin) ( UChar scclass, Bool isErr,
                                   UInt wHI, UInt wLO )
{
   SysRes res;
   res._wHI  = 0;
   res._wLO  = 0;
   res._mode = 0; /* invalid */
   vg_assert(isErr == False || isErr == True);
   vg_assert(sizeof(UWord) == sizeof(UInt));
   switch (scclass) {
      case VG_DARWIN_SYSCALL_CLASS_UNIX:
         res._wLO  = wLO;
         res._wHI  = wHI;
         res._mode = isErr ? SysRes_UNIX_ERR : SysRes_UNIX_OK;
         break;
      case VG_DARWIN_SYSCALL_CLASS_MACH:
         vg_assert(!isErr);
         vg_assert(wHI == 0);
         res._wLO  = wLO;
         res._mode = SysRes_MACH;
         break;
      case VG_DARWIN_SYSCALL_CLASS_MDEP:
         vg_assert(!isErr);
         vg_assert(wHI == 0);
         res._wLO  = wLO;
         res._mode = SysRes_MDEP;
         break;
      default:
         vg_assert(0);
   }
   return res;
}

SysRes VG_(mk_SysRes_amd64_darwin) ( UChar scclass, Bool isErr,
                                     ULong wHI, ULong wLO )
{
   SysRes res;
   res._wHI  = 0;
   res._wLO  = 0;
   res._mode = 0; /* invalid */
   vg_assert(isErr == False || isErr == True);
   vg_assert(sizeof(UWord) == sizeof(ULong));
   switch (scclass) {
      case VG_DARWIN_SYSCALL_CLASS_UNIX:
         res._wLO  = wLO;
         res._wHI  = wHI;
         res._mode = isErr ? SysRes_UNIX_ERR : SysRes_UNIX_OK;
         break;
      case VG_DARWIN_SYSCALL_CLASS_MACH:
         vg_assert(!isErr);
         vg_assert(wHI == 0);
         res._wLO  = wLO;
         res._mode = SysRes_MACH;
         break;
      case VG_DARWIN_SYSCALL_CLASS_MDEP:
         vg_assert(!isErr);
         vg_assert(wHI == 0);
         res._wLO  = wLO;
         res._mode = SysRes_MDEP;
         break;
      default:
         vg_assert(0);
   }
   return res;
}

/* Generic constructors.  We assume (without checking if this makes
   any sense, from the caller's point of view) that these are for the
   UNIX style of syscall. */
SysRes VG_(mk_SysRes_Error) ( UWord err ) {
   SysRes r;
   r._wHI  = 0;
   r._wLO  = err;
   r._mode = SysRes_UNIX_ERR;
   return r;
}

SysRes VG_(mk_SysRes_Success) ( UWord res ) {
   SysRes r;
   r._wHI  = 0;
   r._wLO  = res;
   r._mode = SysRes_UNIX_OK;
   return r;
}


#else
#  error "Unknown OS"
#endif


/* ---------------------------------------------------------------------
   VG_(do_syscall): A function for doing syscalls.
   ------------------------------------------------------------------ */

#if defined(VGP_x86_linux)
/* Incoming args (syscall number + up to 6 args) come on the stack.
   (ie. the C calling convention).

   The syscall number goes in %eax.  The args are passed to the syscall in
   the regs %ebx, %ecx, %edx, %esi, %edi, %ebp, ie. the kernel's syscall
   calling convention.

   %eax gets the return value.  Not sure which registers the kernel
   clobbers, so we preserve all the callee-save regs (%esi, %edi, %ebx,
   %ebp).
*/
extern UWord do_syscall_WRK (
          UWord syscall_no, 
          UWord a1, UWord a2, UWord a3,
          UWord a4, UWord a5, UWord a6
       );
asm(
".text\n"
"do_syscall_WRK:\n"
"	push	%esi\n"
"	push	%edi\n"
"	push	%ebx\n"
"	push	%ebp\n"
"	movl	16+ 4(%esp),%eax\n"
"	movl	16+ 8(%esp),%ebx\n"
"	movl	16+12(%esp),%ecx\n"
"	movl	16+16(%esp),%edx\n"
"	movl	16+20(%esp),%esi\n"
"	movl	16+24(%esp),%edi\n"
"	movl	16+28(%esp),%ebp\n"
"	int	$0x80\n"
"	popl	%ebp\n"
"	popl	%ebx\n"
"	popl	%edi\n"
"	popl	%esi\n"
"	ret\n"
".previous\n"
);

#elif defined(VGP_amd64_linux)
/* Incoming args (syscall number + up to 6 args) come in %rdi, %rsi,
   %rdx, %rcx, %r8, %r9, and the last one on the stack (ie. the C
   calling convention).

   The syscall number goes in %rax.  The args are passed to the syscall in
   the regs %rdi, %rsi, %rdx, %r10, %r8, %r9 (yes, really %r10, not %rcx),
   ie. the kernel's syscall calling convention.

   %rax gets the return value.  %rcx and %r11 are clobbered by the syscall;
   no matter, they are caller-save (the syscall clobbers no callee-save
   regs, so we don't have to do any register saving/restoring).
*/
extern UWord do_syscall_WRK (
          UWord syscall_no, 
          UWord a1, UWord a2, UWord a3,
          UWord a4, UWord a5, UWord a6
       );
asm(
".text\n"
"do_syscall_WRK:\n"
        /* Convert function calling convention --> syscall calling
           convention */
"	movq	%rdi, %rax\n"
"	movq	%rsi, %rdi\n"
"	movq	%rdx, %rsi\n"
"	movq	%rcx, %rdx\n"
"	movq	%r8,  %r10\n"
"	movq	%r9,  %r8\n"
"	movq    8(%rsp), %r9\n"	 /* last arg from stack */
"	syscall\n"
"	ret\n"
".previous\n"
);

#elif defined(VGP_ppc32_linux)
/* Incoming args (syscall number + up to 6 args) come in %r3:%r9.

   The syscall number goes in %r0.  The args are passed to the syscall in
   the regs %r3:%r8, i.e. the kernel's syscall calling convention.

   The %cr0.so bit flags an error.
   We return the syscall return value in %r3, and the %cr0.so in 
   the lowest bit of %r4.
   We return a ULong, of which %r3 is the high word, and %r4 the low.
   No callee-save regs are clobbered, so no saving/restoring is needed.
*/
extern ULong do_syscall_WRK (
          UWord syscall_no, 
          UWord a1, UWord a2, UWord a3,
          UWord a4, UWord a5, UWord a6
       );
asm(
".text\n"
"do_syscall_WRK:\n"
"        mr      0,3\n"
"        mr      3,4\n"
"        mr      4,5\n"
"        mr      5,6\n"
"        mr      6,7\n"
"        mr      7,8\n"
"        mr      8,9\n"
"        sc\n"                  /* syscall: sets %cr0.so on error         */
"        mfcr    4\n"           /* %cr -> low word of return var          */
"        rlwinm  4,4,4,31,31\n" /* rotate flag bit so to lsb, and mask it */
"        blr\n"                 /* and return                             */
".previous\n"
);

#elif defined(VGP_ppc64_linux)
/* Due to the need to return 65 bits of result, this is completely
   different from the ppc32 case.  The single arg register points to a
   7-word block containing the syscall # and the 6 args.  The syscall
   result proper is put in [0] of the block, and %cr0.so is in the
   bottom bit of [1]. */
extern void do_syscall_WRK ( ULong* argblock );
asm(
".align   2\n"
".globl   do_syscall_WRK\n"
".section \".opd\",\"aw\"\n"
".align   3\n"
"do_syscall_WRK:\n"
".quad    .do_syscall_WRK,.TOC.@tocbase,0\n"
".previous\n"
".type    .do_syscall_WRK,@function\n"
".globl   .do_syscall_WRK\n"
".do_syscall_WRK:\n"
"        std  3,-16(1)\n"  /* stash arg */
"        ld   8, 48(3)\n"  /* sc arg 6 */
"        ld   7, 40(3)\n"  /* sc arg 5 */
"        ld   6, 32(3)\n"  /* sc arg 4 */
"        ld   5, 24(3)\n"  /* sc arg 3 */
"        ld   4, 16(3)\n"  /* sc arg 2 */
"        ld   0,  0(3)\n"  /* sc number */
"        ld   3,  8(3)\n"  /* sc arg 1 */
"        sc\n"             /* result in r3 and cr0.so */
"        ld   5,-16(1)\n"  /* reacquire argblock ptr (r5 is caller-save) */
"        std  3,0(5)\n"    /* argblock[0] = r3 */
"        mfcr 3\n"
"        srwi 3,3,28\n"
"        andi. 3,3,1\n"
"        std  3,8(5)\n"    /* argblock[1] = cr0.s0 & 1 */
"        blr\n"
);

#elif defined(VGP_arm_linux)
/* I think the conventions are:
   args  in r0 r1 r2 r3 r4 r5
   sysno in r7
   return value in r0, w/ same conventions as x86-linux, viz r0 in
   -4096 .. -1 is an error value.  All other values are success
   values.
*/
extern UWord do_syscall_WRK (
          UWord a1, UWord a2, UWord a3,
          UWord a4, UWord a5, UWord a6,
          UWord syscall_no
       );
asm(
".text\n"
"do_syscall_WRK:\n"
"         push    {r4, r5, r7}\n"
"         ldr     r4, [sp, #12]\n"
"         ldr     r5, [sp, #16]\n"
"         ldr     r7, [sp, #20]\n"
"         svc     0x0\n"
"         pop     {r4, r5, r7}\n"
"         bx      lr\n"
".previous\n"
);

#elif defined(VGP_x86_darwin)

/* Incoming args (syscall number + up to 8 args) come in on the stack

   The kernel's syscall calling convention is:
   * the syscall number goes in eax
   * the args are passed to the syscall on the stack,
     pushed onto the stack R->L (that is, the usual x86
     calling conventions, with the leftmost arg at the lowest
     address)
   Call instruction:
   * UNIX: sysenter
   * UNIX: int $0x80
   * MACH: int $0x81
   * MDEP: int $0x82
   Note that the call type can be determined from the syscall number;
   there is no need to inspect the actual instruction.  Although obviously
   the instruction must match.
   Return value:
   * MACH,MDEP: the return value comes back in eax
   * UNIX: the return value comes back in edx:eax (hi32:lo32)
   Error:
   * MACH,MDEP: no error is returned
   * UNIX: the carry flag indicates success or failure

   nb here, sizeof(UWord) == sizeof(UInt)
*/

__private_extern__ ULong 
do_syscall_unix_WRK ( UWord a1, UWord a2, UWord a3, /* 4(esp)..12(esp) */
                      UWord a4, UWord a5, UWord a6, /* 16(esp)..24(esp) */
                      UWord a7, UWord a8, /* 28(esp)..32(esp) */
                      UWord syscall_no, /* 36(esp) */
                      /*OUT*/UInt* errflag /* 40(esp) */ );
// Unix syscall: 64-bit return in edx:eax, with LSB in eax
// error indicated by carry flag: clear=good, set=bad
asm(".private_extern _do_syscall_unix_WRK\n"
    "_do_syscall_unix_WRK:\n"
    "        movl    40(%esp), %ecx   \n"  /* assume syscall success */
    "        movl    $0, (%ecx)       \n"
    "        movl    36(%esp), %eax   \n"
    "        int     $0x80            \n"
    "        jnc     1f               \n"  /* jump if success */
    "        movl    40(%esp), %ecx   \n"  /* syscall failed - set *errflag */
    "        movl    $1, (%ecx)       \n"
    "    1:  ret                      \n"
    );

__private_extern__ UInt 
do_syscall_mach_WRK ( UWord a1, UWord a2, UWord a3, /* 4(esp)..12(esp) */
                      UWord a4, UWord a5, UWord a6, /* 16(esp)..24(esp) */
                      UWord a7, UWord a8, /* 28(esp)..32(esp) */
                      UWord syscall_no /* 36(esp) */ );
// Mach trap: 32-bit result in %eax, no error flag
asm(".private_extern _do_syscall_mach_WRK\n"
    "_do_syscall_mach_WRK:\n"
    "        movl    36(%esp), %eax   \n"
    "        int     $0x81            \n"
    "        ret                      \n"
    );

__private_extern__ UInt 
do_syscall_mdep_WRK ( UWord a1, UWord a2, UWord a3, /* 4(esp)..12(esp) */
                      UWord a4, UWord a5, UWord a6, /* 16(esp)..24(esp) */
                      UWord a7, UWord a8, /* 28(esp)..32(esp) */
                      UWord syscall_no /* 36(esp) */ );
// mdep trap: 32-bit result in %eax, no error flag
asm(
    ".private_extern _do_syscall_mdep_WRK\n"
    "_do_syscall_mdep_WRK:\n"
    "        movl    36(%esp), %eax   \n"
    "        int     $0x82            \n"
    "        ret                      \n"
    );


#elif defined(VGP_amd64_darwin)

/* Incoming args (syscall number + up to 8 args) come in registers and stack

   The kernel's syscall calling convention is:
   * the syscall number goes in rax
   * the args are passed to the syscall in registers and the stack
   * the call instruction is 'syscall'
   Return value:
   * MACH,MDEP: the return value comes back in rax
   * UNIX: the return value comes back in rdx:rax (hi64:lo64)
   Error:
   * MACH,MDEP: no error is returned
   * UNIX: the carry flag indicates success or failure

   nb here, sizeof(UWord) == sizeof(ULong)
*/

__private_extern__ UWord 
do_syscall_unix_WRK ( UWord a1, UWord a2, UWord a3, /* rdi, rsi, rdx */
                      UWord a4, UWord a5, UWord a6, /* rcx, r8,  r9 */
                      UWord a7, UWord a8,           /* 8(rsp), 16(rsp) */
                      UWord syscall_no,             /* 24(rsp) */
                      /*OUT*/ULong* errflag,        /* 32(rsp) */
                      /*OUT*/ULong* res2 );         /* 40(rsp) */
// Unix syscall: 128-bit return in rax:rdx, with LSB in rax
// error indicated by carry flag: clear=good, set=bad
asm(".private_extern _do_syscall_unix_WRK\n"
    "_do_syscall_unix_WRK:\n"
    "        movq    %rcx, %r10       \n"  /* pass rcx in r10 instead */
    "        movq    32(%rsp), %rax   \n"  /* assume syscall success */
    "        movq    $0, (%rax)       \n"
    "        movq    24(%rsp), %rax   \n"  /* load syscall_no */
    "        syscall                  \n"
    "        jnc     1f               \n"  /* jump if success */
    "        movq    32(%rsp), %rcx   \n"  /* syscall failed - set *errflag */
    "        movq    $1, (%rcx)       \n"
    "    1:  movq    40(%rsp), %rcx   \n"  /* save 2nd result word */
    "        movq    %rdx, (%rcx)     \n"
    "        retq                     \n"  /* return 1st result word */
    );

__private_extern__ UWord 
do_syscall_mach_WRK ( UWord a1, UWord a2, UWord a3, /* rdi, rsi, rdx */
                      UWord a4, UWord a5, UWord a6, /* rcx, r8,  r9 */
                      UWord a7, UWord a8,           /* 8(rsp), 16(rsp) */
                      UWord syscall_no );           /* 24(rsp) */
// Mach trap: 64-bit result, no error flag
asm(".private_extern _do_syscall_mach_WRK\n"
    "_do_syscall_mach_WRK:\n"
    "        movq    %rcx, %r10       \n"  /* pass rcx in r10 instead */
    "        movq    24(%rsp), %rax   \n"  /* load syscall_no */
    "        syscall                  \n"
    "        retq                     \n"
    );

#elif defined(VGP_s390x_linux)

static UWord do_syscall_WRK (
   UWord syscall_no,
   UWord arg1, UWord arg2, UWord arg3,
   UWord arg4, UWord arg5, UWord arg6
   )
{
   register UWord __arg1 asm("2") = arg1;
   register UWord __arg2 asm("3") = arg2;
   register UWord __arg3 asm("4") = arg3;
   register UWord __arg4 asm("5") = arg4;
   register UWord __arg5 asm("6") = arg5;
   register UWord __arg6 asm("7") = arg6;
   register ULong __svcres asm("2");

   __asm__ __volatile__ (
                 "lgr %%r1,%1\n\t"
                 "svc 0\n\t"
		: "=d" (__svcres)
		: "a" (syscall_no),
		  "0" (__arg1),
		  "d" (__arg2),
		  "d" (__arg3),
		  "d" (__arg4),
		  "d" (__arg5),
		  "d" (__arg6)
		: "1", "cc", "memory");

   return (UWord) (__svcres);
}

#else
#  error Unknown platform
#endif


/* Finally, the generic code.  This sends the call to the right
   helper. */

SysRes VG_(do_syscall) ( UWord sysno, UWord a1, UWord a2, UWord a3,
                                      UWord a4, UWord a5, UWord a6,
                                      UWord a7, UWord a8 )
{
#  if defined(VGP_x86_linux)
   UWord val = do_syscall_WRK(sysno,a1,a2,a3,a4,a5,a6);
   return VG_(mk_SysRes_x86_linux)( val );

#  elif defined(VGP_amd64_linux)
   UWord val = do_syscall_WRK(sysno,a1,a2,a3,a4,a5,a6);
   return VG_(mk_SysRes_amd64_linux)( val );

#  elif defined(VGP_ppc32_linux)
   ULong ret     = do_syscall_WRK(sysno,a1,a2,a3,a4,a5,a6);
   UInt  val     = (UInt)(ret>>32);
   UInt  cr0so   = (UInt)(ret);
   return VG_(mk_SysRes_ppc32_linux)( val, cr0so );

#  elif defined(VGP_ppc64_linux)
   ULong argblock[7];
   argblock[0] = sysno;
   argblock[1] = a1;
   argblock[2] = a2;
   argblock[3] = a3;
   argblock[4] = a4;
   argblock[5] = a5;
   argblock[6] = a6;
   do_syscall_WRK( &argblock[0] );
   return VG_(mk_SysRes_ppc64_linux)( argblock[0], argblock[1] );

#  elif defined(VGP_arm_linux)
   UWord val = do_syscall_WRK(a1,a2,a3,a4,a5,a6,sysno);
   return VG_(mk_SysRes_arm_linux)( val );

#  elif defined(VGP_x86_darwin)
   UInt  wLO = 0, wHI = 0, err = 0;
   ULong u64;
   UChar scclass = VG_DARWIN_SYSNO_CLASS(sysno);
   switch (scclass) {
      case VG_DARWIN_SYSCALL_CLASS_UNIX:
         u64 = do_syscall_unix_WRK(a1,a2,a3,a4,a5,a6,a7,a8,
                                   VG_DARWIN_SYSNO_FOR_KERNEL(sysno), &err);
         wLO = (UInt)u64;
         wHI = (UInt)(u64 >> 32);
         break;
      case VG_DARWIN_SYSCALL_CLASS_MACH:
         wLO = do_syscall_mach_WRK(a1,a2,a3,a4,a5,a6,a7,a8, 
                                   VG_DARWIN_SYSNO_FOR_KERNEL(sysno));
         err = 0;
         break;
      case VG_DARWIN_SYSCALL_CLASS_MDEP:
         wLO = do_syscall_mdep_WRK(a1,a2,a3,a4,a5,a6,a7,a8, 
                                   VG_DARWIN_SYSNO_FOR_KERNEL(sysno));
         err = 0;
         break;
      default:
         vg_assert(0);
         break;
   }
   return VG_(mk_SysRes_x86_darwin)( scclass, err ? True : False, wHI, wLO );

#  elif defined(VGP_amd64_darwin)
   ULong wLO = 0, wHI = 0, err = 0;
   UChar scclass = VG_DARWIN_SYSNO_CLASS(sysno);
   switch (scclass) {
      case VG_DARWIN_SYSCALL_CLASS_UNIX:
         wLO = do_syscall_unix_WRK(a1,a2,a3,a4,a5,a6,a7,a8,
                                   VG_DARWIN_SYSNO_FOR_KERNEL(sysno), &err, &wHI);
         break;
      case VG_DARWIN_SYSCALL_CLASS_MACH:
      case VG_DARWIN_SYSCALL_CLASS_MDEP:
         wLO = do_syscall_mach_WRK(a1,a2,a3,a4,a5,a6,a7,a8, 
                                   VG_DARWIN_SYSNO_FOR_KERNEL(sysno));
         err = 0;
         break;
      default:
         vg_assert(0);
         break;
   }
   return VG_(mk_SysRes_amd64_darwin)( scclass, err ? True : False, wHI, wLO );
  
#elif defined(VGP_s390x_linux)
   UWord val;

   if (sysno == __NR_mmap) {
     ULong argbuf[6];

     argbuf[0] = a1;
     argbuf[1] = a2;
     argbuf[2] = a3;
     argbuf[3] = a4;
     argbuf[4] = a5;
     argbuf[5] = a6;
     val = do_syscall_WRK(sysno,(UWord)&argbuf[0],0,0,0,0,0);
   } else {
     val = do_syscall_WRK(sysno,a1,a2,a3,a4,a5,a6);
   }

   return VG_(mk_SysRes_s390x_linux)( val );
#else
#  error Unknown platform
#endif
}

/* ---------------------------------------------------------------------
   Names of errors.
   ------------------------------------------------------------------ */

/* Return a string which gives the name of an error value.  Note,
   unlike the standard C syserror fn, the returned string is not
   malloc-allocated or writable -- treat it as a constant. 
   TODO: implement this properly. */

const HChar* VG_(strerror) ( UWord errnum )
{
   switch (errnum) {
      case VKI_EPERM:       return "Operation not permitted";
      case VKI_ENOENT:      return "No such file or directory";
      case VKI_ESRCH:       return "No such process";
      case VKI_EINTR:       return "Interrupted system call";
      case VKI_EBADF:       return "Bad file number";
      case VKI_EAGAIN:      return "Try again";
      case VKI_ENOMEM:      return "Out of memory";
      case VKI_EACCES:      return "Permission denied";
      case VKI_EFAULT:      return "Bad address";
      case VKI_EEXIST:      return "File exists";
      case VKI_EINVAL:      return "Invalid argument";
      case VKI_EMFILE:      return "Too many open files";
      case VKI_ENOSYS:      return "Function not implemented";
      case VKI_EOVERFLOW:   return "Value too large for defined data type";
#     if defined(VKI_ERESTARTSYS)
      case VKI_ERESTARTSYS: return "ERESTARTSYS";
#     endif
      default:              return "VG_(strerror): unknown error";
   }
}


/*--------------------------------------------------------------------*/
/*--- end                                                        ---*/
/*--------------------------------------------------------------------*/