[PATCH 5/5] Add frame pointer unwinding for aarch64

Mark Wielaard mark@klomp.org
Tue Apr 25 13:11:00 GMT 2017


From: Ulf Hermann <ulf.hermann@qt.io>

If we don't find any debug information for a given frame, we usually
cannot unwind any further. However, the binary in question might have
been compiled with frame pointers, in which case we can look up the
well known frame pointer locations in the stack snapshot and use them
to bridge the frames without debug information.

Signed-off-by: Ulf Hermann <ulf.hermann@qt.io>
---
 backends/ChangeLog                     |   6 +++
 backends/Makefile.am                   |   2 +-
 backends/aarch64_init.c                |   1 +
 backends/aarch64_unwind.c              |  96 +++++++++++++++++++++++++++++++++
 tests/ChangeLog                        |   7 +++
 tests/Makefile.am                      |   3 ++
 tests/backtrace.aarch64.fp.core.bz2    | Bin 0 -> 8437 bytes
 tests/backtrace.aarch64.fp.exec.bz2    | Bin 0 -> 394972 bytes
 tests/run-backtrace-fp-core-aarch64.sh |  28 ++++++++++
 9 files changed, 142 insertions(+), 1 deletion(-)
 create mode 100644 backends/aarch64_unwind.c
 create mode 100644 tests/backtrace.aarch64.fp.core.bz2
 create mode 100644 tests/backtrace.aarch64.fp.exec.bz2
 create mode 100755 tests/run-backtrace-fp-core-aarch64.sh

diff --git a/backends/ChangeLog b/backends/ChangeLog
index 733e72c..d742bca 100644
--- a/backends/ChangeLog
+++ b/backends/ChangeLog
@@ -6,6 +6,12 @@
 
 2017-02-09  Ulf Hermann  <ulf.hermann@qt.io>
 
+	* aarch64_unwind.c: New file
+	* Makefile.am (aarch64_SRCS): Add aarch64_unwind.c
+	* aarch64_init.c (aarch64_init): Hook aarch64_unwind
+
+2017-02-09  Ulf Hermann  <ulf.hermann@qt.io>
+
 	* x86_64_unwind.c: New file
 	* Makefile.am (x86_64_SRCS): Add x86_64_unwind.c
 	* x86_64_init.c (x86_64_init): Hook x86_64_unwind
diff --git a/backends/Makefile.am b/backends/Makefile.am
index 22eb6ac..ff80a82 100644
--- a/backends/Makefile.am
+++ b/backends/Makefile.am
@@ -80,7 +80,7 @@ am_libebl_arm_pic_a_OBJECTS = $(arm_SRCS:.c=.os)
 
 aarch64_SRCS = aarch64_init.c aarch64_regs.c aarch64_symbol.c	\
 	       aarch64_corenote.c aarch64_retval.c aarch64_cfi.c \
-	       aarch64_initreg.c
+	       aarch64_initreg.c aarch64_unwind.c
 libebl_aarch64_pic_a_SOURCES = $(aarch64_SRCS)
 am_libebl_aarch64_pic_a_OBJECTS = $(aarch64_SRCS:.c=.os)
 
diff --git a/backends/aarch64_init.c b/backends/aarch64_init.c
index 6395f11..0866494 100644
--- a/backends/aarch64_init.c
+++ b/backends/aarch64_init.c
@@ -63,6 +63,7 @@ aarch64_init (Elf *elf __attribute__ ((unused)),
      + ALT_FRAME_RETURN_COLUMN (used when LR isn't used) = 97 DWARF regs. */
   eh->frame_nregs = 97;
   HOOK (eh, set_initial_registers_tid);
+  HOOK (eh, unwind);
 
   return MODVERSION;
 }
diff --git a/backends/aarch64_unwind.c b/backends/aarch64_unwind.c
new file mode 100644
index 0000000..cac4ebd
--- /dev/null
+++ b/backends/aarch64_unwind.c
@@ -0,0 +1,96 @@
+/* Get previous frame state for an existing frame state.
+   Copyright (C) 2016 The Qt Company Ltd.
+   This file is part of elfutils.
+
+   This file is free software; you can redistribute it and/or modify
+   it under the terms of either
+
+     * the GNU Lesser General Public License as published by the Free
+       Software Foundation; either version 3 of the License, or (at
+       your option) any later version
+
+   or
+
+     * the GNU General Public License as published by the Free
+       Software Foundation; either version 2 of the License, or (at
+       your option) any later version
+
+   or both in parallel, as here.
+
+   elfutils is distributed in the hope that it will be useful, but
+   WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   General Public License for more details.
+
+   You should have received copies of the GNU General Public License and
+   the GNU Lesser General Public License along with this program.  If
+   not, see <http://www.gnu.org/licenses/>.  */
+
+#ifdef HAVE_CONFIG_H
+# include <config.h>
+#endif
+
+#define BACKEND aarch64_
+#define FP_REG 29
+#define LR_REG 30
+#define SP_REG 31
+#define FP_OFFSET 0
+#define LR_OFFSET 8
+#define SP_OFFSET 16
+
+#include "libebl_CPU.h"
+
+/* There was no CFI. Maybe we happen to have a frame pointer and can unwind from that?  */
+
+bool
+EBLHOOK(unwind) (Ebl *ebl __attribute__ ((unused)), Dwarf_Addr pc __attribute__ ((unused)),
+                 ebl_tid_registers_t *setfunc, ebl_tid_registers_get_t *getfunc,
+                 ebl_pid_memory_read_t *readfunc, void *arg,
+                 bool *signal_framep __attribute__ ((unused)))
+{
+  Dwarf_Word fp, lr, sp;
+
+  if (!getfunc(LR_REG, 1, &lr, arg))
+    return false;
+
+  if (!getfunc(FP_REG, 1, &fp, arg))
+    fp = 0;
+
+  if (!getfunc(SP_REG, 1, &sp, arg))
+    sp = 0;
+
+  Dwarf_Word newPc, newLr, newFp, newSp;
+
+  // The initial frame is special. We are expected to return lr directly in this case, and we'll
+  // come back to the same frame again in the next round.
+  if ((pc & 0x1) == 0)
+    {
+      newLr = lr;
+      newFp = fp;
+      newSp = sp;
+    }
+  else
+    {
+      if (!readfunc(fp + LR_OFFSET, &newLr, arg))
+        newLr = 0;
+
+      if (!readfunc(fp + FP_OFFSET, &newFp, arg))
+        newFp = 0;
+
+      newSp = fp + SP_OFFSET;
+    }
+
+  newPc = newLr & (~0x1);
+  if (!setfunc(-1, 1, &newPc, arg))
+    return false;
+
+  // These are not fatal if they don't work. They will just prevent unwinding at the next frame.
+  setfunc(LR_REG, 1, &newLr, arg);
+  setfunc(FP_REG, 1, &newFp, arg);
+  setfunc(SP_REG, 1, &newSp, arg);
+
+  // If the fp is invalid, we might still have a valid lr.
+  // But if the fp is valid, then the stack should be moving in the right direction.
+  // Except, if this is the initial frame. Then the stack doesn't move.
+  return newPc != 0 && (fp == 0 || newSp > sp || (pc & 0x1) == 0);
+}
diff --git a/tests/ChangeLog b/tests/ChangeLog
index 67a44f7..b76d643 100644
--- a/tests/ChangeLog
+++ b/tests/ChangeLog
@@ -1,3 +1,10 @@
+2017-02-13  Ulf Hermann  <ulf.hermann@qt.io>
+
+	* Makefile.am: Add test for unwinding with frame pointers on aarch64
+	* backtrace.aarch64.fp.core.bz2: New file
+	* backtrace.aarch64.fp.exec.bz2: New file
+	* run-backtrace-fp-core-aarch64.sh: New file
+
 2017-04-06  Mark Wielaard  <mark@klomp.org>
 
 	* run-backtrace-fp-core-i386.sh: New test.
diff --git a/tests/Makefile.am b/tests/Makefile.am
index 2c82bfd..3a12fe3 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -116,6 +116,7 @@ TESTS = run-arextract.sh run-arsymtest.sh newfile test-nlist \
 	run-backtrace-native-biarch.sh run-backtrace-native-core.sh \
 	run-backtrace-native-core-biarch.sh run-backtrace-core-x86_64.sh \
 	run-backtrace-fp-core-x86_64.sh \
+	run-backtrace-fp-core-aarch64.sh \
 	run-backtrace-core-x32.sh \
 	run-backtrace-core-i386.sh run-backtrace-fp-core-i386.sh \
 	run-backtrace-core-ppc.sh \
@@ -297,6 +298,8 @@ EXTRA_DIST = run-arextract.sh run-arsymtest.sh \
 	     run-backtrace-core-x86_64.sh run-backtrace-core-i386.sh \
 	     run-backtrace-fp-core-x86_64.sh \
 	     run-backtrace-core-x32.sh \
+	     run-backtrace-fp-core-aarch64.sh \
+	     backtrace.aarch64.fp.core.bz2 backtrace.aarch64.fp.exec.bz2 \
 	     backtrace-subr.sh backtrace.i386.core.bz2 backtrace.i386.exec.bz2 \
 	     run-backtrace-fp-core-i386.sh \
 	     backtrace.i386.fp.core.bz2 backtrace.i386.fp.exec.bz2 \

diff --git a/tests/run-backtrace-fp-core-aarch64.sh b/tests/run-backtrace-fp-core-aarch64.sh
new file mode 100755
index 0000000..3b8d4ed
--- /dev/null
+++ b/tests/run-backtrace-fp-core-aarch64.sh
@@ -0,0 +1,28 @@
+#! /bin/bash
+# Copyright (C) 2017 The Qt Company
+# This file is part of elfutils.
+#
+# This file is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# elfutils is distributed in the hope that it will be useful, but
+# WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+. $srcdir/backtrace-subr.sh
+
+# The binary is generated by compiling with eh_frame CFI, but with frame
+# pointers.
+#
+# gcc -static -O2 -fno-omit-frame-pointer -fno-asynchronous-unwind-tables \
+#     -D_GNU_SOURCE -pthread -o tests/backtrace.aarch64.fp.exec -I. -Ilib \
+#     tests/backtrace-child.c#
+# The core is generated by calling the binary with --gencore
+
+check_core aarch64.fp
-- 
1.8.3.1



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