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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 common-user/safe-syscall.S
*
* Ported to LoongArch by WANG Xuerui <git@xen0n.name>
*
* Based on safe-syscall.inc.S code for RISC-V,
* originally written by Richard Henderson <rth@twiddle.net>
* Copyright (C) 2018 Linaro, 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 is nearly the same as C:
* we enter with a0 == &signal_pending
* a1 == syscall number
* a2 ... a7 == syscall arguments
* and return the result in a0
* and the syscall instruction needs
* a7 == syscall number
* a0 ... a5 == syscall arguments
* and returns the result in a0
* Shuffle everything around appropriately.
*/
move $t0, $a0 /* signal_pending pointer */
move $t1, $a1 /* syscall number */
move $a0, $a2 /* syscall arguments */
move $a1, $a3
move $a2, $a4
move $a3, $a5
move $a4, $a6
move $a5, $a7
move $a7, $t1
/*
* We need to preserve the signal_pending pointer but t0 is
* clobbered by syscalls on LoongArch, so we need to move it
* somewhere else, ideally both preserved across syscalls and
* clobbered by procedure calls so we don't have to allocate a
* stack frame; a6 is just the register we want here.
*/
move $a6, $t0
/*
* 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 */
ld.w $t1, $a6, 0
bnez $t1, 2f
syscall 0
safe_syscall_end:
/* code path for having successfully executed the syscall */
li.w $t2, -4096
bgtu $a0, $t2, 0f
jr $ra
/* code path setting errno */
0: sub.d $a0, $zero, $a0
b safe_syscall_set_errno_tail
/* code path when we didn't execute the syscall */
2: li.w $a0, QEMU_ERESTARTSYS
b safe_syscall_set_errno_tail
.cfi_endproc
.size safe_syscall_base, .-safe_syscall_base
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