linux-user/host/s390x/safe-syscall.inc.S

   1 /*
   2  * safe-syscall.inc.S : host-specific assembly fragment
   3  * to handle signals occurring at the same time as system calls.
   4  * This is intended to be included by linux-user/safe-syscall.S
   5  *
   6  * Written by Richard Henderson <rth@twiddle.net>
   7  * Copyright (C) 2016 Red Hat, Inc.
   8  *
   9  * This work is licensed under the terms of the GNU GPL, version 2 or later.
  10  * See the COPYING file in the top-level directory.
  11  */
  12
  13         .global safe_syscall_base
  14         .global safe_syscall_start
  15         .global safe_syscall_end
  16         .type   safe_syscall_base, @function
  17
  18         /* This is the entry point for making a system call. The calling
  19          * convention here is that of a C varargs function with the
  20          * first argument an 'int *' to the signal_pending flag, the
  21          * second one the system call number (as a 'long'), and all further
  22          * arguments being syscall arguments (also 'long').
  23          */
  24 safe_syscall_base:
  25         .cfi_startproc
  26         stmg    %r6,%r15,48(%r15)       /* save all call-saved registers */
  27         .cfi_offset %r15,-40
  28         .cfi_offset %r14,-48
  29         .cfi_offset %r13,-56
  30         .cfi_offset %r12,-64
  31         .cfi_offset %r11,-72
  32         .cfi_offset %r10,-80
  33         .cfi_offset %r9,-88
  34         .cfi_offset %r8,-96
  35         .cfi_offset %r7,-104
  36         .cfi_offset %r6,-112
  37         lgr     %r1,%r15
  38         lg      %r0,8(%r15)             /* load eos */
  39         aghi    %r15,-160
  40         .cfi_adjust_cfa_offset 160
  41         stg     %r1,0(%r15)             /* store back chain */
  42         stg     %r0,8(%r15)             /* store eos */
  43
  44         /*
  45          * The syscall calling convention isn't the same as the C one:
  46          * we enter with r2 == &signal_pending
  47          *               r3 == syscall number
  48          *               r4, r5, r6, (stack) == syscall arguments
  49          *               and return the result in r2
  50          * and the syscall instruction needs
  51          *               r1 == syscall number
  52          *               r2 ... r7 == syscall arguments
  53          *               and returns the result in r2
  54          * Shuffle everything around appropriately.
  55          */
  56         lgr     %r8,%r2                 /* signal_pending pointer */
  57         lgr     %r1,%r3                 /* syscall number */
  58         lgr     %r2,%r4                 /* syscall args */
  59         lgr     %r3,%r5
  60         lgr     %r4,%r6
  61         lmg     %r5,%r7,320(%r15)
  62
  63         /* This next sequence of code works in conjunction with the
  64          * rewind_if_safe_syscall_function(). If a signal is taken
  65          * and the interrupted PC is anywhere between 'safe_syscall_start'
  66          * and 'safe_syscall_end' then we rewind it to 'safe_syscall_start'.
  67          * The code sequence must therefore be able to cope with this, and
  68          * the syscall instruction must be the final one in the sequence.
  69          */
  70 safe_syscall_start:
  71         /* if signal_pending is non-zero, don't do the call */
  72         icm     %r0,15,0(%r8)
  73         jne     2f
  74         svc     0
  75 safe_syscall_end:
  76
  77         /* code path for having successfully executed the syscall */
  78         lg      %r15,0(%r15)            /* load back chain */
  79         .cfi_remember_state
  80         .cfi_adjust_cfa_offset -160
  81         lmg     %r6,%r15,48(%r15)       /* load saved registers */
  82
  83         lghi    %r0, -4095              /* check for syscall error */
  84         clgr    %r2, %r0
  85         blr     %r14                    /* return on success */
  86         lcr     %r2, %r2                /* create positive errno */
  87         jg      safe_syscall_set_errno_tail
  88         .cfi_restore_state
  89
  90         /* code path when we didn't execute the syscall */
  91 2:      lg      %r15,0(%r15)            /* load back chain */
  92         .cfi_adjust_cfa_offset -160
  93         lmg     %r6,%r15,48(%r15)       /* load saved registers */
  94         lghi    %r2, TARGET_ERESTARTSYS
  95         jg      safe_syscall_set_errno_tail
  96
  97         .cfi_endproc
  98         .size   safe_syscall_base, .-safe_syscall_base