5bfd125ec8
FreeBSD system calls return positive errno. On the 4 hosts for which we have support, error is indicated by the C bit set or clear. Reviewed-by: Warner Losh <imp@bsdimp.com> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
89 lines
3.2 KiB
ArmAsm
89 lines
3.2 KiB
ArmAsm
/*
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* safe-syscall.inc.S : host-specific assembly fragment
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* to handle signals occurring at the same time as system calls.
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* This is intended to be included by common-user/safe-syscall.S
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*
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* Written by Richard Henderson <rth@twiddle.net>
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* Copyright (C) 2016 Red Hat, Inc.
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*
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* This work is licensed under the terms of the GNU GPL, version 2 or later.
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* See the COPYING file in the top-level directory.
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*/
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.global safe_syscall_base
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.global safe_syscall_start
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.global safe_syscall_end
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.type safe_syscall_base, #function
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.type safe_syscall_start, #function
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.type safe_syscall_end, #function
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/* This is the entry point for making a system call. The calling
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* convention here is that of a C varargs function with the
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* first argument an 'int *' to the signal_pending flag, the
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* second one the system call number (as a 'long'), and all further
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* arguments being syscall arguments (also 'long').
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*/
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safe_syscall_base:
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.cfi_startproc
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/* The syscall calling convention isn't the same as the
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* C one:
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* we enter with x0 == &signal_pending
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* x1 == syscall number
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* x2 ... x7, (stack) == syscall arguments
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* and return the result in x0
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* and the syscall instruction needs
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* x8 == syscall number
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* x0 ... x6 == syscall arguments
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* and returns the result in x0
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* Shuffle everything around appropriately.
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*/
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mov x9, x0 /* signal_pending pointer */
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mov x8, x1 /* syscall number */
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mov x0, x2 /* syscall arguments */
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mov x1, x3
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mov x2, x4
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mov x3, x5
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mov x4, x6
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mov x5, x7
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ldr x6, [sp]
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/* This next sequence of code works in conjunction with the
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* rewind_if_safe_syscall_function(). If a signal is taken
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* and the interrupted PC is anywhere between 'safe_syscall_start'
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* and 'safe_syscall_end' then we rewind it to 'safe_syscall_start'.
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* The code sequence must therefore be able to cope with this, and
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* the syscall instruction must be the final one in the sequence.
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*/
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safe_syscall_start:
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/* if signal_pending is non-zero, don't do the call */
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ldr w10, [x9]
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cbnz w10, 2f
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svc 0x0
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safe_syscall_end:
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/* code path for having successfully executed the syscall */
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#if defined(__linux__)
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/* Linux kernel returns (small) negative errno. */
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cmp x0, #-4096
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b.hi 0f
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#elif defined(__FreeBSD__)
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/* FreeBSD kernel returns positive errno and C bit set. */
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b.cs 1f
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#else
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#error "unsupported os"
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#endif
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ret
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#if defined(__linux__)
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/* code path setting errno */
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0: neg w0, w0
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b safe_syscall_set_errno_tail
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#endif
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/* code path when we didn't execute the syscall */
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2: mov w0, #QEMU_ERESTARTSYS
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1: b safe_syscall_set_errno_tail
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.cfi_endproc
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.size safe_syscall_base, .-safe_syscall_base
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