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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
/* 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
stmg %r6,%r15,48(%r15) /* save all call-saved registers */
.cfi_offset %r15,-40
.cfi_offset %r14,-48
.cfi_offset %r13,-56
.cfi_offset %r12,-64
.cfi_offset %r11,-72
.cfi_offset %r10,-80
.cfi_offset %r9,-88
.cfi_offset %r8,-96
.cfi_offset %r7,-104
.cfi_offset %r6,-112
lgr %r1,%r15
lg %r0,8(%r15) /* load eos */
aghi %r15,-160
.cfi_adjust_cfa_offset 160
stg %r1,0(%r15) /* store back chain */
stg %r0,8(%r15) /* store eos */
/*
* The syscall calling convention isn't the same as the C one:
* we enter with r2 == &signal_pending
* r3 == syscall number
* r4, r5, r6, (stack) == syscall arguments
* and return the result in r2
* and the syscall instruction needs
* r1 == syscall number
* r2 ... r7 == syscall arguments
* and returns the result in r2
* Shuffle everything around appropriately.
*/
lgr %r8,%r2 /* signal_pending pointer */
lgr %r1,%r3 /* syscall number */
lgr %r2,%r4 /* syscall args */
lgr %r3,%r5
lgr %r4,%r6
lmg %r5,%r7,320(%r15)
/* 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 */
icm %r0,15,0(%r8)
jne 2f
svc 0
safe_syscall_end:
/* code path for having successfully executed the syscall */
lg %r15,0(%r15) /* load back chain */
.cfi_remember_state
.cfi_adjust_cfa_offset -160
lmg %r6,%r15,48(%r15) /* load saved registers */
lghi %r0, -4095 /* check for syscall error */
clgr %r2, %r0
blr %r14 /* return on success */
lcr %r2, %r2 /* create positive errno */
jg safe_syscall_set_errno_tail
.cfi_restore_state
/* code path when we didn't execute the syscall */
2: lg %r15,0(%r15) /* load back chain */
.cfi_adjust_cfa_offset -160
lmg %r6,%r15,48(%r15) /* load saved registers */
lghi %r2, QEMU_ERESTARTSYS
jg safe_syscall_set_errno_tail
.cfi_endproc
.size safe_syscall_base, .-safe_syscall_base
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