qemu/common-user/host/ppc64/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 common-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

        .text

        /* 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 _CALL_ELF == 2
safe_syscall_base:
        .cfi_startproc
        .localentry safe_syscall_base,0
#else
        .section ".opd","aw"
        .align  3
safe_syscall_base:
        .quad   .L.safe_syscall_base,.TOC.@tocbase,0
        .previous
.L.safe_syscall_base:
        .cfi_startproc
#endif
        /* We enter with r3 == &signal_pending
         *               r4 == syscall number
         *               r5 ... r10 == syscall arguments
         *               and return the result in r3
         * and the syscall instruction needs
         *               r0 == syscall number
         *               r3 ... r8 == syscall arguments
         *               and returns the result in r3
         * Shuffle everything around appropriately.
         */
        std     14, 16(1) /* Preserve r14 in SP+16 */
        .cfi_offset 14, 16
        mr      14, 3   /* signal_pending */
        mr      0, 4    /* syscall number */
        mr      3, 5    /* syscall arguments */
        mr      4, 6
        mr      5, 7
        mr      6, 8
        mr      7, 9
        mr      8, 10

        /* 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 */
        lwz     12, 0(14)
        cmpwi   0, 12, 0
        bne-    2f
        sc
safe_syscall_end:
        /* code path when we did execute the syscall */
        ld      14, 16(1) /* restore r14 */
        bso-    1f
        blr

        /* code path when we didn't execute the syscall */
2:      ld      14, 16(1) /* restore r14 */
        addi    3, 0, QEMU_ERESTARTSYS

        /* code path setting errno */
1:      b       safe_syscall_set_errno_tail
        nop     /* per abi, for the linker to modify */

        .cfi_endproc

#if _CALL_ELF == 2
        .size   safe_syscall_base, .-safe_syscall_base
#else
        .size   safe_syscall_base, .-.L.safe_syscall_base
        .size   .L.safe_syscall_base, .-.L.safe_syscall_base
#endif