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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 Peter Maydell <peter.maydell@linaro.org>
*
* Copyright (C) 2016 Linaro Limited
*
* 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
/* 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:
.cfi_startproc
/* Save ebx esi edi ebp, as the calling convention requires */
pushl %ebp
.cfi_adjust_cfa_offset 4
.cfi_rel_offset ebp, 0
pushl %edi
.cfi_adjust_cfa_offset 4
.cfi_rel_offset edi, 0
pushl %esi
.cfi_adjust_cfa_offset 4
.cfi_rel_offset esi, 0
pushl %ebx
.cfi_adjust_cfa_offset 4
.cfi_rel_offset ebx, 0
/* The syscall calling convention isn't the same as the
* C one:
* we enter with all arguments on the stack:
* *signal_pending
* syscall number
* syscall arguments
* and return the result in eax
* and the syscall instruction needs
* eax == syscall number
* ebx, ecx, edx, esi, edi, ebp == syscall arguments
* and returns the result in eax
* Shuffle everything around appropriately.
*
* At this point the stack layout is:
* 48(%esp) syscall arg 6
* 44(%esp) syscall arg 5
* 40(%esp) syscall arg 4
* 36(%esp) syscall arg 3
* 32(%esp) syscall arg 2
* 28(%esp) syscall arg 1
* 24(%esp) syscall number
* 20(%esp) *signal_pending
* 16(%esp) return address
* 12(%esp) saved EBP
* 8(%esp) saved EDI
* 4(%esp) saved ESI
* (%esp) saved EBX
*/
/* syscall arguments */
movl 48(%esp), %ebp
movl 44(%esp), %edi
movl 40(%esp), %esi
movl 36(%esp), %edx
movl 32(%esp), %ecx
movl 28(%esp), %ebx
/* 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.
* For i386 we have absolutely no spare registers at the point of
* the syscall, so we must load *signal_pending and the syscall
* number off the stack inside the start/end section.
*/
safe_syscall_start:
/* *signal_pending */
movl 20(%esp), %eax
/* if signal_pending is non-zero, don't do the call */
testl $1, (%eax)
jnz return_ERESTARTSYS
movl 24(%esp), %eax
int $0x80
safe_syscall_end:
/* code path for having successfully executed the syscall */
.cfi_remember_state
popl %ebx
.cfi_adjust_cfa_offset -4
.cfi_restore ebx
popl %esi
.cfi_adjust_cfa_offset -4
.cfi_restore esi
popl %edi
.cfi_adjust_cfa_offset -4
.cfi_restore edi
popl %ebp
.cfi_adjust_cfa_offset -4
.cfi_restore ebp
ret
return_ERESTARTSYS:
/* code path when we didn't execute the syscall */
.cfi_restore_state
mov $-TARGET_ERESTARTSYS, %eax
popl %ebx
.cfi_adjust_cfa_offset -4
.cfi_restore ebx
popl %esi
.cfi_adjust_cfa_offset -4
.cfi_restore esi
popl %edi
.cfi_adjust_cfa_offset -4
.cfi_restore edi
popl %ebp
.cfi_adjust_cfa_offset -4
.cfi_restore ebp
ret
.cfi_endproc
.size safe_syscall_base, .-safe_syscall_base
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