fb084237a3
Brown bag time: offset 0 from esp is the return address,
offset 4 is the first argument.
Fixes: d7478d4229 ("common-user: Fix tail calls to safe_syscall_set_errno_tail")
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
128 lines
4.3 KiB
ArmAsm
128 lines
4.3 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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/* 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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push %ebp
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.cfi_adjust_cfa_offset 4
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.cfi_rel_offset ebp, 0
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push %esi
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.cfi_adjust_cfa_offset 4
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.cfi_rel_offset esi, 0
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push %edi
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.cfi_adjust_cfa_offset 4
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.cfi_rel_offset edi, 0
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push %ebx
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.cfi_adjust_cfa_offset 4
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.cfi_rel_offset ebx, 0
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/* The syscall calling convention isn't the same as the C one:
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* we enter with 0(%esp) == return address
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* 4(%esp) == &signal_pending
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* 8(%esp) == syscall number
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* 12(%esp) ... 32(%esp) == syscall arguments
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* and return the result in eax
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* and the syscall instruction needs
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* eax == syscall number
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* ebx, ecx, edx, esi, edi, ebp == syscall arguments
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* and returns the result in eax
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* Shuffle everything around appropriately.
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* Note the 16 bytes that we pushed to save registers.
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*/
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mov 12+16(%esp), %ebx /* the syscall arguments */
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mov 16+16(%esp), %ecx
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mov 20+16(%esp), %edx
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mov 24+16(%esp), %esi
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mov 28+16(%esp), %edi
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mov 32+16(%esp), %ebp
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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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mov 4+16(%esp), %eax /* signal_pending */
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cmpl $0, (%eax)
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jnz 2f
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mov 8+16(%esp), %eax /* syscall number */
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int $0x80
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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 $-4095, %eax
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jae 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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jc 1f
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#else
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#error "unsupported os"
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#endif
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pop %ebx
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.cfi_remember_state
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.cfi_adjust_cfa_offset -4
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.cfi_restore ebx
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pop %edi
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.cfi_adjust_cfa_offset -4
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.cfi_restore edi
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pop %esi
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.cfi_adjust_cfa_offset -4
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.cfi_restore esi
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pop %ebp
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.cfi_adjust_cfa_offset -4
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.cfi_restore ebp
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ret
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.cfi_restore_state
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#if defined(__linux__)
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0: neg %eax
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jmp 1f
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#endif
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/* code path when we didn't execute the syscall */
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2: mov $QEMU_ERESTARTSYS, %eax
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/* code path setting errno */
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1: pop %ebx
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.cfi_adjust_cfa_offset -4
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.cfi_restore ebx
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pop %edi
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.cfi_adjust_cfa_offset -4
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.cfi_restore edi
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pop %esi
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.cfi_adjust_cfa_offset -4
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.cfi_restore esi
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pop %ebp
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.cfi_adjust_cfa_offset -4
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.cfi_restore ebp
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mov %eax, 4(%esp)
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jmp 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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