91 lines
3.2 KiB
ArmAsm
91 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 <richard.henderson@linaro.org>
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* Copyright (C) 2021 Linaro, 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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.text
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.balign 4
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.register %g2, #scratch
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.register %g3, #scratch
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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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#define STACK_BIAS 2047
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#define WINDOW_SIZE 16 * 8
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#define PARAM(N) STACK_BIAS + WINDOW_SIZE + N * 8
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/*
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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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/*
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* The syscall calling convention isn't the same as the C one:
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* we enter with o0 == &signal_pending
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* o1 == syscall number
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* o2 ... o5, (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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* g1 == syscall number
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* o0 ... o5 == syscall arguments
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* and returns the result in o0
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* Shuffle everything around appropriately.
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*/
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mov %o0, %g2 /* signal_pending pointer */
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mov %o1, %g1 /* syscall number */
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mov %o2, %o0 /* syscall arguments */
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mov %o3, %o1
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mov %o4, %o2
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mov %o5, %o3
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ldx [%sp + PARAM(6)], %o4
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ldx [%sp + PARAM(7)], %o5
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/*
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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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lduw [%g2], %g3
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brnz,pn %g3, 2f
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nop
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ta 0x6d
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safe_syscall_end:
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/* code path for having successfully executed the syscall */
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bcs,pn %xcc, 1f
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nop
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retl
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nop
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/* code path when we didn't execute the syscall */
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2: set QEMU_ERESTARTSYS, %o0
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/* code path setting errno */
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1: mov %o7, %g1
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call safe_syscall_set_errno_tail
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mov %g1, %o7
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.cfi_endproc
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.size safe_syscall_base, .-safe_syscall_base
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