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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
*
* Written by Richard Henderson <richard.henderson@linaro.org>
* Copyright (C) 2021 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.
*/
.text
.balign 4
.register %g2, #scratch
.register %g3, #scratch
.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
#define STACK_BIAS 2047
#define PARAM(N) STACK_BIAS + N*8
/*
* 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 o0 == &signal_pending
* o1 == syscall number
* o2 ... o5, (stack) == syscall arguments
* and return the result in x0
* and the syscall instruction needs
* g1 == syscall number
* o0 ... o5 == syscall arguments
* and returns the result in o0
* Shuffle everything around appropriately.
*/
mov %o0, %g2 /* signal_pending pointer */
mov %o1, %g1 /* syscall number */
mov %o2, %o0 /* syscall arguments */
mov %o3, %o1
mov %o4, %o2
mov %o5, %o3
ldx [%sp + PARAM(6)], %o4
ldx [%sp + PARAM(7)], %o5
/*
* 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 */
lduw [%g2], %g3
brnz,pn %g3, 2f
nop
ta 0x6d
safe_syscall_end:
/* code path for having successfully executed the syscall */
bcs,pn %xcc, 1f
nop
ret
nop
/* code path when we didn't execute the syscall */
2: set QEMU_ERESTARTSYS, %o0
/* code path setting errno */
1: mov %o7, %g1
call safe_syscall_set_errno_tail
mov %g1, %o7
.cfi_endproc
.size safe_syscall_base, .-safe_syscall_base
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