9e024732f5
Use cfi directives in the x86-64 safe_syscall to allow gdb to get backtraces right from within it. (In particular this will be quite a common situation if the user interrupts QEMU while it's in a blocked safe-syscall: at the point of the syscall insn RBP is in use for something else, and so gdb can't find the frame then without assistance.) Signed-off-by: Peter Maydell <peter.maydell@linaro.org> Reviewed-by: Richard Henderson <rth@twiddle.net> Reviewed-by: Richard Henderson <rth@twiddle.net> Signed-off-by: Riku Voipio <riku.voipio@linaro.org>
92 lines
3.6 KiB
ArmAsm
92 lines
3.6 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 linux-user/safe-syscall.S
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*
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* Copyright (C) 2015 Timothy Edward Baldwin <T.E.Baldwin99@members.leeds.ac.uk>
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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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* We return a long which is the syscall's return value, which
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* may be negative-errno on failure. Conversion to the
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* -1-and-errno-set convention is done by the calling wrapper.
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*/
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safe_syscall_base:
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.cfi_startproc
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/* This saves a frame pointer and aligns the stack for the syscall.
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* (It's unclear if the syscall ABI has the same stack alignment
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* requirements as the userspace function call ABI, but better safe than
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* sorry. Appendix A2 of http://www.x86-64.org/documentation/abi.pdf
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* does not list any ABI differences regarding stack alignment.)
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*/
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push %rbp
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.cfi_adjust_cfa_offset 8
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.cfi_rel_offset rbp, 0
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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 rdi == *signal_pending
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* rsi == syscall number
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* rdx, rcx, r8, r9, (stack), (stack) == syscall arguments
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* and return the result in rax
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* and the syscall instruction needs
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* rax == syscall number
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* rdi, rsi, rdx, r10, r8, r9 == syscall arguments
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* and returns the result in rax
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* Shuffle everything around appropriately.
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* Note that syscall will trash rcx and r11.
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*/
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mov %rsi, %rax /* syscall number */
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mov %rdi, %rbp /* signal_pending pointer */
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/* and the syscall arguments */
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mov %rdx, %rdi
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mov %rcx, %rsi
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mov %r8, %rdx
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mov %r9, %r10
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mov 16(%rsp), %r8
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mov 24(%rsp), %r9
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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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testl $1, (%rbp)
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jnz return_ERESTARTSYS
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syscall
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safe_syscall_end:
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/* code path for having successfully executed the syscall */
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pop %rbp
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.cfi_remember_state
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.cfi_def_cfa_offset 8
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.cfi_restore rbp
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ret
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return_ERESTARTSYS:
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/* code path when we didn't execute the syscall */
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.cfi_restore_state
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mov $-TARGET_ERESTARTSYS, %rax
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pop %rbp
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.cfi_def_cfa_offset 8
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.cfi_restore rbp
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ret
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.cfi_endproc
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.size safe_syscall_base, .-safe_syscall_base
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