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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
.type safe_syscall_start, #function
.type safe_syscall_end, #function
/* 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').
*/
safe_syscall_base:
.cfi_startproc
/* The syscall calling convention isn't the same as the
* C one:
* we enter with x0 == &signal_pending
* x1 == syscall number
* x2 ... x7, (stack) == syscall arguments
* and return the result in x0
* and the syscall instruction needs
* x8 == syscall number
* x0 ... x6 == syscall arguments
* and returns the result in x0
* Shuffle everything around appropriately.
*/
mov x9, x0 /* signal_pending pointer */
mov x8, x1 /* syscall number */
mov x0, x2 /* syscall arguments */
mov x1, x3
mov x2, x4
mov x3, x5
mov x4, x6
mov x5, x7
ldr x6, [sp]
/* 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 w10, [x9]
cbnz w10, 2f
svc 0x0
safe_syscall_end:
/* code path for having successfully executed the syscall */
cmp x0, #-4096
b.hi 0f
ret
/* code path setting errno */
0: neg w0, w0
b safe_syscall_set_errno_tail
/* code path when we didn't execute the syscall */
2: mov w0, #QEMU_ERESTARTSYS
b safe_syscall_set_errno_tail
.cfi_endproc
.size safe_syscall_base, .-safe_syscall_base
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