Add frame pointer unwinding for aarch64 and relax backtrace testcases.

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.

Relax the backtrace core testcases a little by allowing a duplicate
sigusr2 frame or a backtrace ending with an invalid register. Both of
which can happen if the frame pointer unwinder guesses slightly wrong.

Signed-off-by: Ulf Hermann <ulf.hermann@qt.io>
Signed-off-by: Mark Wielaard <mark@klomp.org>

4 files changed, 91 insertions, 1 deletions

diff --git a/backends/ChangeLog b/backends/ChangeLog
index 8b1c4f52..1ac5bab3 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 22eb6ac6..ff80a82c 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 6395f117..08664943 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 00000000..e0a7e96e
--- /dev/null
+++ b/backends/aarch64_unwind.c
@@ -0,0 +1,83 @@
+/* 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 (lr == 0 || !setfunc(-1, 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 newLr, newFp, newSp;
+
+  if (!readfunc(fp + LR_OFFSET, &newLr, arg))
+    newLr = 0;
+
+  if (!readfunc(fp + FP_OFFSET, &newFp, arg))
+    newFp = 0;
+
+  newSp = fp + SP_OFFSET;
+
+  // 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.
+  return fp == 0 || newSp > sp;
+}