Add i386 frame pointer unwinder.

Add a simple i386_unwind.c frame pointer unwinder as fallback if DWARF/CFI
unwinding fails.

Signed-off-by: Mark Wielaard <mark@klomp.org>

4 files changed, 93 insertions, 2 deletions

diff --git a/backends/ChangeLog b/backends/ChangeLog
index 04f579da..8b1c4f52 100644
--- a/backends/ChangeLog
+++ b/backends/ChangeLog
@@ -1,3 +1,9 @@
+2017-04-06  Mark Wielaard  <mark@klomp.org>
+
+	* i386_unwind.c: New file.
+	* i386_init.c: Hook i386_unwind.
+	* Makefile.am (i386_SRCS): Add i386_unwind.c
+
 2017-02-09  Ulf Hermann  <ulf.hermann@qt.io>
 
 	* x86_64_unwind.c: New file
diff --git a/backends/Makefile.am b/backends/Makefile.am
index 60917b92..22eb6ac6 100644
--- a/backends/Makefile.am
+++ b/backends/Makefile.am
@@ -48,7 +48,7 @@ libdw = ../libdw/libdw.so
 
 i386_SRCS = i386_init.c i386_symbol.c i386_corenote.c i386_cfi.c \
 	    i386_retval.c i386_regs.c i386_auxv.c i386_syscall.c \
-	    i386_initreg.c
+	    i386_initreg.c i386_unwind.c
 cpu_i386 = ../libcpu/libcpu_i386.a
 libebl_i386_pic_a_SOURCES = $(i386_SRCS)
 am_libebl_i386_pic_a_OBJECTS = $(i386_SRCS:.c=.os)
diff --git a/backends/i386_init.c b/backends/i386_init.c
index 515d5ac0..fc1587a9 100644
--- a/backends/i386_init.c
+++ b/backends/i386_init.c
@@ -1,5 +1,5 @@
 /* Initialization of i386 specific backend library.
-   Copyright (C) 2000-2009, 2013 Red Hat, Inc.
+   Copyright (C) 2000-2009, 2013, 2017 Red Hat, Inc.
    This file is part of elfutils.
    Written by Ulrich Drepper <drepper@redhat.com>, 2000.
 
@@ -65,6 +65,7 @@ i386_init (Elf *elf __attribute__ ((unused)),
   /* gcc/config/ #define DWARF_FRAME_REGISTERS.  For i386 it is 17, why?  */
   eh->frame_nregs = 9;
   HOOK (eh, set_initial_registers_tid);
+  HOOK (eh, unwind);
 
   return MODVERSION;
 }
diff --git a/backends/i386_unwind.c b/backends/i386_unwind.c
new file mode 100644
index 00000000..5c9a5de0
--- /dev/null
+++ b/backends/i386_unwind.c
@@ -0,0 +1,84 @@
+/* Get previous frame state for an existing frame state using frame pointers.
+   Copyright (C) 2017 Red Hat, Inc.
+   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>
+
+#define BACKEND i386_
+#include "libebl_CPU.h"
+
+/* Register numbers for frame and stack pointers.  We take advantage of
+   them being next to each other when calling getfunc and setfunc.  */
+#define ESP 4
+#define EBP (ESP + 1)
+
+/* Most basic frame pointer chasing with EBP as frame pointer.
+   PC = *(FP + 4), SP = FP + 8, FP = *FP.  */
+bool
+i386_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)))
+{
+  /* sp = 0, fp = 1 */
+  Dwarf_Word regs[2];
+
+  /* Get current stack and frame pointers.  */
+  if (! getfunc (ESP, 2, regs, arg))
+    return false;
+
+  Dwarf_Word sp = regs[0];
+  Dwarf_Word fp = regs[1];
+
+  /* Sanity check.  We only support traditional stack frames.  */
+  if (fp == 0 || sp == 0 || fp < sp)
+    return false;
+
+  /* Get the return address from the stack, it is our new pc.  */
+  Dwarf_Word ret_addr;
+  if (! readfunc (fp + 4, &ret_addr, arg) || ret_addr == 0)
+    return false;
+
+  /* Get new sp and fp.  Sanity check again.  */
+  sp = fp + 8;
+  if (! readfunc (fp, &fp, arg) || fp == 0 || sp >= fp)
+    return false;
+
+  /* Set new sp, fp and pc.  */
+  regs[0] = sp;
+  regs[1] = fp;
+  if (! setfunc (ESP, 2, regs, arg) || ! setfunc (-1, 1, &ret_addr, arg))
+    return false;
+
+  return true;
+}