linux-user/host/s390x/safe-syscall.inc.S

/*
 * 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').
	 * 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
	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 */
	lt	%r0,0(%r8)
	jne	2f
	svc	0
safe_syscall_end:

1:	lg	%r15,0(%r15)		/* load back chain */
	.cfi_remember_state
	.cfi_adjust_cfa_offset -160
	lmg	%r6,%r15,48(%r15)	/* load saved registers */
	br	%r14
	.cfi_restore_state
2:	lghi	%r2, -TARGET_ERESTARTSYS
	j	1b
	.cfi_endproc

	.size	safe_syscall_base, .-safe_syscall_base