example.c

#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)