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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.
*/
#include "sys/regdef.h"
#include "sys/asm.h"
.text
.set nomips16
.set reorder
.global safe_syscall_start
.global safe_syscall_end
.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').
*/
#if _MIPS_SIM == _ABIO32
/* 8 * 4 = 32 for outgoing parameters; 1 * 4 for s0 save; 1 * 4 for align. */
#define FRAME 40
#define OFS_S0 32
#else
/* 1 * 8 for s0 save; 1 * 8 for align. */
#define FRAME 16
#define OFS_S0 0
#endif
NESTED(safe_syscall_base, FRAME, ra)
.cfi_startproc
PTR_ADDIU sp, sp, -FRAME
.cfi_adjust_cfa_offset FRAME
REG_S s0, OFS_S0(sp)
.cfi_rel_offset s0, OFS_S0
#if _MIPS_SIM == _ABIO32
/*
* The syscall calling convention is nearly the same as C:
* we enter with a0 == &signal_pending
* a1 == syscall number
* a2, a3, stack == syscall arguments
* and return the result in a0
* and the syscall instruction needs
* v0 == syscall number
* a0 ... a3, stack == syscall arguments
* and returns the result in v0
* Shuffle everything around appropriately.
*/
move s0, a0 /* signal_pending pointer */
move v0, a1 /* syscall number */
move a0, a2 /* syscall arguments */
move a1, a3
lw a2, FRAME+16(sp)
lw a3, FRAME+20(sp)
lw t4, FRAME+24(sp)
lw t5, FRAME+28(sp)
lw t6, FRAME+32(sp)
lw t7, FRAME+40(sp)
sw t4, 16(sp)
sw t5, 20(sp)
sw t6, 24(sp)
sw t7, 28(sp)
#else
/*
* 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
* v0 == syscall number
* a0 ... a5 == syscall arguments
* and returns the result in v0
* Shuffle everything around appropriately.
*/
move s0, a0 /* signal_pending pointer */
move v0, a1 /* syscall number */
move a0, a2 /* syscall arguments */
move a1, a3
move a2, a4
move a3, a5
move a4, a6
move a5, a7
#endif
/*
* 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 */
lw t1, 0(s0)
bnez t1, 2f
syscall
safe_syscall_end:
/* code path for having successfully executed the syscall */
REG_L s0, OFS_S0(sp)
PTR_ADDIU sp, sp, FRAME
.cfi_remember_state
.cfi_adjust_cfa_offset -FRAME
.cfi_restore s0
bnez a3, 1f
jr ra
.cfi_restore_state
/* code path when we didn't execute the syscall */
2: REG_L s0, OFS_S0(sp)
PTR_ADDIU sp, sp, FRAME
.cfi_adjust_cfa_offset -FRAME
.cfi_restore s0
li v0, QEMU_ERESTARTSYS
/* code path setting errno */
/*
* We didn't setup GP on entry, optimistic of the syscall success.
* We must do so now to load the address of the helper, as required
* by the ABI, into t9.
*
* Note that SETUP_GPX and SETUP_GPX64 are themselves conditional,
* so we can simply let the one that's not empty succeed.
*/
1: USE_ALT_CP(t0)
SETUP_GPX(t1)
SETUP_GPX64(t0, t1)
PTR_LA t9, safe_syscall_set_errno_tail
jr t9
.cfi_endproc
END(safe_syscall_base)
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