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Decorate the aarch64 signal trampoline with CFI attributes easing unw…
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…inding

Now, the unwinders (in backtrace(3) and similar) can unwind properly
the stack from a signal handler.
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@krytarowski
krytarowski committed Oct 13, 2020
1 parent f6bb4c9 commit e5e90f1
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Showing 2 changed files with 76 additions and 2 deletions.
32 changes: 31 additions & 1 deletion lib/libc/arch/aarch64/genassym.cf
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Original file line number Diff line number Diff line change
@@ -1,4 +1,4 @@
# $NetBSD: genassym.cf,v 1.2 2020/05/10 14:05:59 skrll Exp $
# $NetBSD: genassym.cf,v 1.3 2020/10/13 01:59:55 kamil Exp $

#-
# Copyright (c) 2014 The NetBSD Foundation, Inc.
Expand Down Expand Up @@ -34,6 +34,36 @@ include <ucontext.h>
include <setjmp.h>

define _UC_REGS_X0 offsetof(ucontext_t, uc_mcontext.__gregs[_REG_X0])
define _UC_REGS_X1 offsetof(ucontext_t, uc_mcontext.__gregs[_REG_X1])
define _UC_REGS_X2 offsetof(ucontext_t, uc_mcontext.__gregs[_REG_X2])
define _UC_REGS_X3 offsetof(ucontext_t, uc_mcontext.__gregs[_REG_X3])
define _UC_REGS_X4 offsetof(ucontext_t, uc_mcontext.__gregs[_REG_X4])
define _UC_REGS_X5 offsetof(ucontext_t, uc_mcontext.__gregs[_REG_X5])
define _UC_REGS_X6 offsetof(ucontext_t, uc_mcontext.__gregs[_REG_X6])
define _UC_REGS_X7 offsetof(ucontext_t, uc_mcontext.__gregs[_REG_X7])
define _UC_REGS_X8 offsetof(ucontext_t, uc_mcontext.__gregs[_REG_X8])
define _UC_REGS_X9 offsetof(ucontext_t, uc_mcontext.__gregs[_REG_X9])
define _UC_REGS_X10 offsetof(ucontext_t, uc_mcontext.__gregs[_REG_X10])
define _UC_REGS_X11 offsetof(ucontext_t, uc_mcontext.__gregs[_REG_X11])
define _UC_REGS_X12 offsetof(ucontext_t, uc_mcontext.__gregs[_REG_X12])
define _UC_REGS_X13 offsetof(ucontext_t, uc_mcontext.__gregs[_REG_X13])
define _UC_REGS_X14 offsetof(ucontext_t, uc_mcontext.__gregs[_REG_X14])
define _UC_REGS_X15 offsetof(ucontext_t, uc_mcontext.__gregs[_REG_X15])
define _UC_REGS_X16 offsetof(ucontext_t, uc_mcontext.__gregs[_REG_X16])
define _UC_REGS_X17 offsetof(ucontext_t, uc_mcontext.__gregs[_REG_X17])
define _UC_REGS_X18 offsetof(ucontext_t, uc_mcontext.__gregs[_REG_X18])
define _UC_REGS_X19 offsetof(ucontext_t, uc_mcontext.__gregs[_REG_X19])
define _UC_REGS_X20 offsetof(ucontext_t, uc_mcontext.__gregs[_REG_X20])
define _UC_REGS_X21 offsetof(ucontext_t, uc_mcontext.__gregs[_REG_X21])
define _UC_REGS_X22 offsetof(ucontext_t, uc_mcontext.__gregs[_REG_X22])
define _UC_REGS_X23 offsetof(ucontext_t, uc_mcontext.__gregs[_REG_X23])
define _UC_REGS_X24 offsetof(ucontext_t, uc_mcontext.__gregs[_REG_X24])
define _UC_REGS_X25 offsetof(ucontext_t, uc_mcontext.__gregs[_REG_X25])
define _UC_REGS_X26 offsetof(ucontext_t, uc_mcontext.__gregs[_REG_X26])
define _UC_REGS_X27 offsetof(ucontext_t, uc_mcontext.__gregs[_REG_X27])
define _UC_REGS_X28 offsetof(ucontext_t, uc_mcontext.__gregs[_REG_X28])
define _UC_REGS_X29 offsetof(ucontext_t, uc_mcontext.__gregs[_REG_X29])
define _UC_REGS_X30 offsetof(ucontext_t, uc_mcontext.__gregs[_REG_X30])
define _UC_REGS_SP offsetof(ucontext_t, uc_mcontext.__gregs[_REG_SP])
define _UC_REGS_PC offsetof(ucontext_t, uc_mcontext.__gregs[_REG_PC])

Expand Down
46 changes: 45 additions & 1 deletion lib/libc/arch/aarch64/sys/__sigtramp2.S
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Original file line number Diff line number Diff line change
@@ -1,4 +1,4 @@
/* $NetBSD: __sigtramp2.S,v 1.1 2014/08/10 05:47:37 matt Exp $ */
/* $NetBSD: __sigtramp2.S,v 1.2 2020/10/13 01:59:55 kamil Exp $ */

/*-
* Copyright (c) 2014 The NetBSD Foundation, Inc.
Expand Down Expand Up @@ -30,6 +30,7 @@
*/

#include "SYS.h"
#include "assym.h"

/*
* The ARM signal trampoline is invoked only to return from
Expand All @@ -40,11 +41,54 @@
* ucontext structure
* sp-> siginfo structure
* and x28 points to the ucontext
*
* The unwind entry includes the one byte prior to the trampoline
* because the unwinder will look up (return PC - 1) while unwinding.
* Normally (return PC - 1) computes an address inside the call
* instruction that created the child frame, but here there is no call
* instruction so we have to manually add padding.
*/
.cfi_startproc simple
.cfi_signal_frame
.cfi_def_cfa x28, 0
.cfi_offset x0, _UC_REGS_X0
.cfi_offset x1, _UC_REGS_X1
.cfi_offset x2, _UC_REGS_X2
.cfi_offset x3, _UC_REGS_X3
.cfi_offset x4, _UC_REGS_X4
.cfi_offset x5, _UC_REGS_X5
.cfi_offset x6, _UC_REGS_X6
.cfi_offset x7, _UC_REGS_X7
.cfi_offset x8, _UC_REGS_X8
.cfi_offset x9, _UC_REGS_X9
.cfi_offset x10, _UC_REGS_X10
.cfi_offset x11, _UC_REGS_X11
.cfi_offset x12, _UC_REGS_X12
.cfi_offset x13, _UC_REGS_X13
.cfi_offset x14, _UC_REGS_X14
.cfi_offset x15, _UC_REGS_X15
.cfi_offset x16, _UC_REGS_X16
.cfi_offset x17, _UC_REGS_X17
.cfi_offset x18, _UC_REGS_X18
.cfi_offset x19, _UC_REGS_X19
.cfi_offset x20, _UC_REGS_X20
.cfi_offset x21, _UC_REGS_X21
.cfi_offset x22, _UC_REGS_X22
.cfi_offset x23, _UC_REGS_X23
.cfi_offset x24, _UC_REGS_X24
.cfi_offset x25, _UC_REGS_X25
.cfi_offset x26, _UC_REGS_X26
.cfi_offset x27, _UC_REGS_X27
.cfi_offset x28, _UC_REGS_X28
.cfi_offset x29, _UC_REGS_X29
.cfi_offset x30, _UC_REGS_X30
/* The unwinder will use the CFA to restore X31 (SP). */
nop
ENTRY_NP(__sigtramp_siginfo_2)
mov x0, x28 /* set the arg */
SYSTRAP(setcontext) /* and call setcontext */

/* If that failed, exit with the error code. */
SYSTRAP(exit)
.cfi_endproc
END(__sigtramp_siginfo_2)

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