4 files changed, 102 insertions, 1 deletions
diff --git a/backends/ChangeLog b/backends/ChangeLog
index e2f05295..930854ba 100644
--- a/backends/ChangeLog
+++ b/backends/ChangeLog
@@ -1,3 +1,9 @@
+2017-04-26  Ulf Hermann  <[email protected]>
+
+	* arm_unwind.c: New file
+	* Makefile.am (arm_SRCS): Add arm_unwind.c
+	* arm_init.c (arm_init): Hook arm_unwind
+
 2017-04-28  Ulf Hermann <[email protected]>
 
 	* Makefile.am: Have the backend file names follow the platform's
diff --git a/backends/Makefile.am b/backends/Makefile.am
index 55ff871f..526fcb99 100644
--- a/backends/Makefile.am
+++ b/backends/Makefile.am
@@ -80,7 +80,8 @@ libebl_alpha_pic_a_SOURCES = $(alpha_SRCS)
 am_libebl_alpha_pic_a_OBJECTS = $(alpha_SRCS:.c=.os)
 
 arm_SRCS = arm_init.c arm_symbol.c arm_regs.c arm_corenote.c \
-	   arm_auxv.c arm_attrs.c arm_retval.c arm_cfi.c arm_initreg.c
+	   arm_auxv.c arm_attrs.c arm_retval.c arm_cfi.c arm_initreg.c \
+	   arm_unwind.c
 libebl_arm_pic_a_SOURCES = $(arm_SRCS)
 am_libebl_arm_pic_a_OBJECTS = $(arm_SRCS:.c=.os)
 
diff --git a/backends/arm_init.c b/backends/arm_init.c
index caadac65..4fa0601a 100644
--- a/backends/arm_init.c
+++ b/backends/arm_init.c
@@ -68,6 +68,7 @@ arm_init (Elf *elf __attribute__ ((unused)),
   /* We only unwind the core integer registers.  */
   eh->frame_nregs = 16;
   HOOK (eh, set_initial_registers_tid);
+  HOOK (eh, unwind);
 
   /* Bit zero encodes whether an function address is THUMB or ARM. */
   eh->func_addr_mask = ~(GElf_Addr)1;
diff --git a/backends/arm_unwind.c b/backends/arm_unwind.c
new file mode 100644
index 00000000..3d1e1f25
--- /dev/null
+++ b/backends/arm_unwind.c
@@ -0,0 +1,93 @@
+/* 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
+
+#include <stdlib.h>
+#include <assert.h>
+
+#ifndef BACKEND
+#define BACKEND arm_
+
+// Actually, in THUMB mode it's r7. Let's ignore this.
+#define FP_REG 11
+#define LR_REG 14
+#define SP_REG 13
+
+// The offsets are a mess. gcc-generated code with -mapcs-frame has FP and LR the other way around.
+// We make it work with QV4.
+#define FP_OFFSET 0
+#define LR_OFFSET 4
+#define SP_OFFSET 8
+#endif
+
+#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 = 0, sp = 0; // have to be initialized because registers are 32bit only
+
+  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;
+
+  if (!setfunc(-1, 1, &newLr, arg))
+    return false;
+
+  // unset the "thumb" bit. We get LR without thumb bit, so let's also pass it on that way.
+  newLr &= 0xfffffffe;
+
+  // 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 newLr != 0 && (fp == 0 || newSp > sp);
+}