linux-user: Provide safe_syscall for aarch64

#ifndef QEMU_HOSTDEP_H

#define QEMU_HOSTDEP_H

/* We have a safe-syscall.inc.S */

#define HAVE_SAFE_SYSCALL

#ifndef __ASSEMBLER__

/* These are defined by the safe-syscall.inc.S file */

extern char safe_syscall_start[];

extern char safe_syscall_end[];

/* Adjust the signal context to rewind out of safe-syscall if we're in it */

static inline void rewind_if_in_safe_syscall(void *puc)

{

    struct ucontext *uc = puc;

    __u64 *pcreg = &uc->uc_mcontext.pc;

    if (*pcreg > (uintptr_t)safe_syscall_start

        && *pcreg < (uintptr_t)safe_syscall_end) {

        *pcreg = (uintptr_t)safe_syscall_start;

    }

}

#endif /* __ASSEMBLER__ */

#endif

/*

 * 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

	.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').

	 * 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

	/* The syscall calling convention isn't the same as the

	 * C one:

	 * we enter with x0 == *signal_pending

	 *               x1 == syscall number

	 *               x2 ... x7, (stack) == syscall arguments

	 *               and return the result in x0

	 * and the syscall instruction needs

	 *               x8 == syscall number

	 *               x0 ... x7 == syscall arguments

	 *               and returns the result in x0

	 * Shuffle everything around appropriately.

	 */

	mov	x9, x0		/* signal_pending pointer */

	mov	x8, x1		/* syscall number */

	mov	x0, x2		/* syscall arguments */

	mov	x1, x3

	mov	x2, x4

	mov	x3, x5

	mov	x4, x6

	mov	x6, x7

	ldr	x7, [sp]

	/* 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 */

	ldr	w10, [x9]

	cbnz	w10, 0f 

	svc	0x0

safe_syscall_end:

	/* code path for having successfully executed the syscall */

	ret

0:

	/* code path when we didn't execute the syscall */

	mov	x0, #-TARGET_ERESTARTSYS

	ret

	.cfi_endproc

	.size	safe_syscall_base, .-safe_syscall_base