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/*
* safe-syscall.inc.S : host-specific assembly fragment
* to handle signals occurring at the same time as system calls.
* This is intended to be included by linux-user/safe-syscall.S
*
* Written by Richard Henderson <rth@twiddle.net>
* Copyright (C) 2016 Red Hat, Inc.
*
* This work is licensed under the terms of the GNU GPL, version 2 or later.
* See the COPYING file in the top-level directory.
*/
.global safe_syscall_base
.global safe_syscall_start
.global safe_syscall_end
.type safe_syscall_base, %function
.cfi_sections .debug_frame
.text
.syntax unified
.arm
.align 2
/* This is the entry point for making a system call. The calling
* convention here is that of a C varargs function with the
* first argument an 'int *' to the signal_pending flag, the
* second one the system call number (as a 'long'), and all further
* arguments being syscall arguments (also 'long').
* We return a long which is the syscall's return value, which
* may be negative-errno on failure. Conversion to the
* -1-and-errno-set convention is done by the calling wrapper.
*/
safe_syscall_base:
.fnstart
.cfi_startproc
mov r12, sp /* save entry stack */
push { r4, r5, r6, r7, r8, lr }
.save { r4, r5, r6, r7, r8, lr }
.cfi_adjust_cfa_offset 24
.cfi_rel_offset r4, 0
.cfi_rel_offset r5, 4
.cfi_rel_offset r6, 8
.cfi_rel_offset r7, 12
.cfi_rel_offset r8, 16
.cfi_rel_offset lr, 20
/* The syscall calling convention isn't the same as the C one:
* we enter with r0 == *signal_pending
* r1 == syscall number
* r2, r3, [sp+0] ... [sp+12] == syscall arguments
* and return the result in r0
* and the syscall instruction needs
* r7 == syscall number
* r0 ... r6 == syscall arguments
* and returns the result in r0
* Shuffle everything around appropriately.
* Note the 16 bytes that we pushed to save registers.
*/
mov r8, r0 /* copy signal_pending */
mov r7, r1 /* syscall number */
mov r0, r2 /* syscall args */
mov r1, r3
ldm r12, { r2, r3, r4, r5, r6 }
/* This next sequence of code works in conjunction with the
* rewind_if_safe_syscall_function(). If a signal is taken
* and the interrupted PC is anywhere between 'safe_syscall_start'
* and 'safe_syscall_end' then we rewind it to 'safe_syscall_start'.
* The code sequence must therefore be able to cope with this, and
* the syscall instruction must be the final one in the sequence.
*/
safe_syscall_start:
/* if signal_pending is non-zero, don't do the call */
ldr r12, [r8] /* signal_pending */
tst r12, r12
bne 1f
swi 0
safe_syscall_end:
/* code path for having successfully executed the syscall */
pop { r4, r5, r6, r7, r8, pc }
1:
/* code path when we didn't execute the syscall */
ldr r0, =-TARGET_ERESTARTSYS
pop { r4, r5, r6, r7, r8, pc }
.fnend
.cfi_endproc
.size safe_syscall_base, .-safe_syscall_base
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