[Libunwind-devel] [PATCH 2/4] Add module for parsing ARM-specific unwind tables

[Ken Werner]

From: Zachary T Welch <address@hidden>

Handles lookup, extracting unwind entries, and decoding the entry
using a callback mechanism.

Signed-off-by: Ken Werner <address@hidden>
---
 include/tdep-arm/ex_tables.h   |  128 +++++++++
 include/tdep-arm/libunwind_i.h |    2 +
 src/Makefile.am                |    3 +-
 src/arm/ex_tables.c            |  600 ++++++++++++++++++++++++++++++++++++++++
 src/elfxx.h                    |    4 +-
 5 files changed, 734 insertions(+), 3 deletions(-)
 create mode 100644 include/tdep-arm/ex_tables.h
 create mode 100644 src/arm/ex_tables.c

diff --git a/include/tdep-arm/ex_tables.h b/include/tdep-arm/ex_tables.h
new file mode 100644
index 0000000..3805c60
--- /dev/null
+++ b/include/tdep-arm/ex_tables.h
@@ -0,0 +1,128 @@
+/* libunwind - a platform-independent unwind library
+   Copyright 2011 Linaro Limited
+
+This file is part of libunwind.
+
+Permission is hereby granted, free of charge, to any person obtaining
+a copy of this software and associated documentation files (the
+"Software"), to deal in the Software without restriction, including
+without limitation the rights to use, copy, modify, merge, publish,
+distribute, sublicense, and/or sell copies of the Software, and to
+permit persons to whom the Software is furnished to do so, subject to
+the following conditions:
+
+The above copyright notice and this permission notice shall be
+included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.  */
+
+#ifndef ARM_EX_TABLES_H
+#define ARM_EX_TABLES_H
+
+struct arm_exidx_entry {
+  uint32_t addr;
+  uint32_t data;
+};
+
+struct arm_exidx_table {
+  const char *name;
+  struct arm_exidx_entry *start;
+  struct arm_exidx_entry *end;
+  void *start_addr;
+  void *end_addr;
+#ifdef ARM_EXIDX_TABLE_MALLOC
+  struct arm_exidx_table *next;
+#endif
+};
+
+
+typedef enum arm_exbuf_cmd {
+  ARM_EXIDX_CMD_FINISH,
+  ARM_EXIDX_CMD_DATA_PUSH,
+  ARM_EXIDX_CMD_DATA_POP,
+  ARM_EXIDX_CMD_REG_POP,
+  ARM_EXIDX_CMD_REG_TO_SP,
+  ARM_EXIDX_CMD_VFP_POP,
+  ARM_EXIDX_CMD_WREG_POP,
+  ARM_EXIDX_CMD_WCGR_POP,
+  ARM_EXIDX_CMD_RESERVED,
+  ARM_EXIDX_CMD_REFUSED,
+} arm_exbuf_cmd_t;
+
+enum arm_exbuf_cmd_flags {
+  ARM_EXIDX_VFP_SHIFT_16 = 1 << 16,
+  ARM_EXIDX_VFP_DOUBLE = 1 << 17,
+};
+
+#define ARM_EXBUF_START(x)     (((x) >> 4) & 0x0f)
+#define ARM_EXBUF_COUNT(x)     ((x) & 0x0f)
+#define ARM_EXBUF_END(x)       (ARM_EXBUF_START(x) + ARM_EXBUF_COUNT(x))
+
+struct arm_exbuf_callback_data {
+  uint8_t ops[11];
+  uint8_t n_ops;
+  arm_exbuf_cmd_t cmd;
+  uint32_t data;
+  void *cb_data;
+};
+
+typedef int (*arm_exbuf_callback_t)(struct arm_exbuf_callback_data *aecb);
+
+static inline void *
+prel31_to_addr (void *addr)
+{
+  uint32_t offset = ((long)*(uint32_t *)addr << 1) >> 1;
+  return (char *)addr + offset;
+}
+
+int arm_exidx_init_local (const char *appname);
+
+int arm_exidx_table_add (const char *name,
+    struct arm_exidx_entry *start, struct arm_exidx_entry *end);
+struct arm_exidx_table *arm_exidx_table_find (void *pc);
+struct arm_exidx_entry *arm_exidx_table_lookup (
+               struct arm_exidx_table *table, void *pc);
+
+void arm_exidx_section_find (struct elf_image *ei,
+               Elf_W (Shdr) **exidx, Elf_W (Shdr) **extbl);
+int arm_exidx_entry_lookup (struct elf_image *ei,
+               Elf_W (Shdr) *exidx, uint32_t ip);
+int arm_exidx_entry_extract (struct elf_image *ei,
+               Elf_W (Shdr) *exidx, Elf_W (Shdr) *extbl,
+               unsigned i, uint8_t *buf);
+int arm_exidx_extract (struct arm_exidx_entry *entry, uint8_t *buf);
+
+int arm_exidx_decode (const uint8_t *buf, uint8_t len,
+               arm_exbuf_callback_t cb, void *cb_data);
+
+struct arm_stackframe {
+  void *fp;
+  void *sp;
+  void *lr;
+  void *pc;
+};
+
+struct arm_exidx_vrs {
+  uint32_t vrs[16];
+};
+
+enum arm_exidx_vrs_regs {
+  FP_thumb = 7,
+  FP_arm = 11,
+  SP = 13,
+  LR = 14,
+  PC = 15,
+};
+
+void arm_exidx_frame_to_vrs(struct arm_stackframe *f, struct arm_exidx_vrs *s);
+int arm_exidx_vrs_to_frame(struct arm_exidx_vrs *s, struct arm_stackframe *f);
+
+int arm_exidx_vrs_callback (struct arm_exbuf_callback_data *aecd);
+
+#endif // ARM_EX_TABLES_H
diff --git a/include/tdep-arm/libunwind_i.h b/include/tdep-arm/libunwind_i.h
index 5f02ed0..a565d9b 100644
--- a/include/tdep-arm/libunwind_i.h
+++ b/include/tdep-arm/libunwind_i.h
@@ -34,6 +34,7 @@ WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE 
SOFTWARE.  */
 #include "elf32.h"
 #include "mempool.h"
 #include "dwarf.h"
+#include "ex_tables.h"
 
 struct unw_addr_space
   {
@@ -54,6 +55,7 @@ struct unw_addr_space
 struct cursor
   {
     struct dwarf_cursor dwarf;         /* must be first */
+    struct arm_stackframe frame;
     unw_word_t sigcontext_addr;
   };
 
diff --git a/src/Makefile.am b/src/Makefile.am
index b87cbab..7c1505a 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -137,7 +137,8 @@ libunwind_la_LIBADD += $(LIBUNWIND_ELF)
 # The list of files that go into libunwind and libunwind-arm:
 noinst_HEADERS += arm/init.h arm/offsets.h arm/unwind_i.h
 libunwind_la_SOURCES_arm_common = $(libunwind_la_SOURCES_common)           \
-       arm/is_fpreg.c arm/regname.c
+       arm/is_fpreg.c arm/regname.c                                        \
+       arm/ex_tables.c arm/ex_tables.h
 
 # The list of files that go into libunwind:
 libunwind_la_SOURCES_arm = $(libunwind_la_SOURCES_arm_common)              \
diff --git a/src/arm/ex_tables.c b/src/arm/ex_tables.c
new file mode 100644
index 0000000..3b5e8ef
--- /dev/null
+++ b/src/arm/ex_tables.c
@@ -0,0 +1,600 @@
+/* libunwind - a platform-independent unwind library
+   Copyright 2011 Linaro Limited
+
+This file is part of libunwind.
+
+Permission is hereby granted, free of charge, to any person obtaining
+a copy of this software and associated documentation files (the
+"Software"), to deal in the Software without restriction, including
+without limitation the rights to use, copy, modify, merge, publish,
+distribute, sublicense, and/or sell copies of the Software, and to
+permit persons to whom the Software is furnished to do so, subject to
+the following conditions:
+
+The above copyright notice and this permission notice shall be
+included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.  */
+
+#include "libunwind_i.h"
+
+#define ARM_EXIDX_CANT_UNWIND  0x00000001
+#define ARM_EXIDX_COMPACT      0x80000000
+
+#define ARM_EXTBL_OP_FINISH    0xb0
+
+#ifdef ARM_EXIDX_TABLE_MALLOC
+static struct arm_exidx_table *arm_exidx_table_list;
+#else
+#define ARM_EXIDX_TABLE_LIMIT 32
+static struct arm_exidx_table arm_exidx_tables[ARM_EXIDX_TABLE_LIMIT];
+static unsigned arm_exidx_table_count = 0;
+#endif
+static const char *arm_exidx_appname;
+
+static void
+arm_exidx_table_reset_all (void)
+{
+#ifdef ARM_EXIDX_TABLE_MALLOC
+  while (NULL != arm_exidx_table_list)
+    {
+      struct arm_exidx_table *next = arm_exidx_table_list->next;
+      free (arm_exidx_table_list);
+      arm_exidx_table_list = next;
+    }
+#else
+  arm_exidx_table_count = 0;
+#endif
+}
+
+HIDDEN int
+arm_exidx_table_add (const char *name,
+    struct arm_exidx_entry *start, struct arm_exidx_entry *end)
+{
+#ifdef ARM_EXIDX_TABLE_MALLOC
+  struct arm_exidx_table *table = malloc (sizeof (*table));
+  if (NULL == table)
+    return -1;
+  table->next = arm_exidx_table_list;
+  arm_exidx_table_list = table;
+#else
+  if (arm_exidx_table_count >= ARM_EXIDX_TABLE_LIMIT)
+    return -1;
+  struct arm_exidx_table *table = &arm_exidx_tables[arm_exidx_table_count++];
+#endif
+  table->name = name;
+  table->start = start;
+  table->end = end;
+  table->start_addr = prel31_to_addr (&start->addr);
+  table->end_addr = prel31_to_addr (&(end - 1)->addr);
+  Debug (2, "name=%s, range=%p-%p, addr=%p-%p\n",
+      name, start, end, table->start_addr, table->end_addr);
+  return 0;
+}
+
+/**
+ * Located the appropriate unwind table
+ */
+HIDDEN struct arm_exidx_table *
+arm_exidx_table_find (void *pc)
+{
+  struct arm_exidx_table *table;
+#ifdef ARM_EXIDX_TABLE_MALLOC
+  for (table = arm_exidx_table_list; table != NULL; table = table->next)
+  {
+#else
+  unsigned i;
+  for (i = 0; i < arm_exidx_table_count; i++)
+  {
+    table = &arm_exidx_tables[i];
+#endif
+    if (pc >= table->start_addr && pc < table->end_addr)
+      return table;
+  }
+  return NULL;
+}
+
+/* Based on Linux arm/arm/kernel/unwind.c:search_index() */
+HIDDEN struct arm_exidx_entry *
+arm_exidx_table_lookup (struct arm_exidx_table *table, void *pc)
+{
+  struct arm_exidx_entry *first = table->start, *last = table->end - 1;
+  if (pc < prel31_to_addr (&first->addr))
+    return NULL;
+  else if (pc >= prel31_to_addr (&last->addr))
+    return last;
+  while (first < last - 1)
+    {
+      struct arm_exidx_entry *mid = first + ((last - first + 1) >> 1);
+      if (pc < prel31_to_addr (&mid->addr))
+       last = mid;
+      else
+       first = mid;
+    }
+  return first;
+}
+
+static inline int
+arm_exidx_frame_reg(void *pc)
+{
+  return ((unsigned)pc & 1) ? FP_thumb : FP_arm;
+}
+
+HIDDEN void
+arm_exidx_frame_to_vrs(struct arm_stackframe *f, struct arm_exidx_vrs *s)
+{
+  int fp_reg = arm_exidx_frame_reg(f->pc);
+  s->vrs[fp_reg] = (uint32_t)f->fp;
+  s->vrs[SP] = (uint32_t)f->sp;
+  s->vrs[LR] = (uint32_t)f->lr;
+  s->vrs[PC] = 0;
+}
+
+HIDDEN int
+arm_exidx_vrs_to_frame(struct arm_exidx_vrs *s, struct arm_stackframe *f)
+{
+  if (s->vrs[PC] == 0)
+    s->vrs[PC] = s->vrs[LR];
+
+  if (f->pc == (void *)s->vrs[PC])
+    return -1;
+
+  int fp_reg = arm_exidx_frame_reg(f->pc);
+  f->fp = (void *)s->vrs[fp_reg];
+  f->sp = (void *)s->vrs[SP];
+  f->lr = (void *)s->vrs[LR];
+  f->pc = (void *)s->vrs[PC];
+
+  return 0;
+}
+
+HIDDEN int
+arm_exidx_vrs_callback (struct arm_exbuf_callback_data *aecd)
+{
+  struct arm_exidx_vrs *s = aecd->cb_data;
+  int ret = 0, i;
+  switch (aecd->cmd)
+    {
+      case ARM_EXIDX_CMD_FINISH:
+       break;
+      case ARM_EXIDX_CMD_DATA_PUSH:
+       Debug (2, "vsp = vsp - %d\n", aecd->data);
+       s->vrs[SP] -= aecd->data;
+       break;
+      case ARM_EXIDX_CMD_DATA_POP:
+       Debug (2, "vsp = vsp + %d\n", aecd->data);
+       s->vrs[SP] += aecd->data;
+       break;
+      case ARM_EXIDX_CMD_REG_POP:
+       for (i = 0; i < 16; i++)
+         if (aecd->data & (1 << i))
+           {
+             s->vrs[i] = *(uint32_t*)s->vrs[SP];
+             s->vrs[SP] += 4;
+             Debug (2, "pop {r%d}\n", i);
+           }
+       break;
+      case ARM_EXIDX_CMD_REG_TO_SP:
+       assert (aecd->data < 16);
+       Debug (2, "vsp = r%d\n", aecd->data);
+       s->vrs[SP] = s->vrs[aecd->data];
+       break;
+      case ARM_EXIDX_CMD_VFP_POP:
+       /* Skip VFP registers, but be sure to adjust stack */
+       for (i = ARM_EXBUF_START (aecd->data); i < ARM_EXBUF_END (aecd->data); 
i++)
+         s->vrs[SP] += 8;
+       if (!(aecd->data & ARM_EXIDX_VFP_DOUBLE))
+         s->vrs[SP] += 4;
+       break;
+      case ARM_EXIDX_CMD_WREG_POP:
+       for (i = ARM_EXBUF_START (aecd->data); i < ARM_EXBUF_END (aecd->data); 
i++)
+         s->vrs[SP] += 8;
+       break;
+      case ARM_EXIDX_CMD_WCGR_POP:
+       for (i = 0; i < 4; i++)
+         if (aecd->data & (1 << i))
+           s->vrs[SP] += 4;
+       break;
+      case ARM_EXIDX_CMD_REFUSED:
+      case ARM_EXIDX_CMD_RESERVED:
+       ret = -1;
+       break;
+    }
+  return ret;
+}
+
+HIDDEN int
+arm_exidx_decode (const uint8_t *buf, uint8_t len,
+               arm_exbuf_callback_t cb, void *cb_data)
+{
+#define READ_OP() aecb.ops[aecb.n_ops++] = *buf++
+  const uint8_t *end = buf + len;
+  int ret;
+
+  assert(buf != NULL);
+  assert(cb != NULL);
+  while (buf < end)
+    {
+      struct arm_exbuf_callback_data aecb = { .cb_data = cb_data };
+      uint8_t op = READ_OP ();
+      if ((op & 0xc0) == 0x00)
+       {
+         aecb.cmd = ARM_EXIDX_CMD_DATA_POP;
+         aecb.data = (((int)op & 0x3f) << 2) + 4;
+       }
+      else if ((op & 0xc0) == 0x40)
+       {
+         aecb.cmd = ARM_EXIDX_CMD_DATA_PUSH;
+         aecb.data = (((int)op & 0x3f) << 2) + 4;
+       }
+      else if ((op & 0xf0) == 0x80)
+       {
+         uint8_t op2 = READ_OP ();
+         if (op == 0x80 && op2 == 0x00)
+           aecb.cmd = ARM_EXIDX_CMD_REFUSED;
+         else
+           {
+             aecb.cmd = ARM_EXIDX_CMD_REG_POP;
+             aecb.data = ((op & 0xf) << 8) | op2;
+             aecb.data = aecb.data << 4;
+           }
+       }
+      else if ((op & 0xf0) == 0x90)
+       {
+         if (op == 0x9d || op == 0x9f)
+           aecb.cmd = ARM_EXIDX_CMD_RESERVED;
+         else
+           {
+             aecb.cmd = ARM_EXIDX_CMD_REG_TO_SP;
+             aecb.data = op & 0x0f;
+           }
+       }
+      else if ((op & 0xf0) == 0xa0)
+       {
+         unsigned end = (op & 0x07);
+         aecb.data = (1 << (end + 1)) - 1;
+         aecb.data = aecb.data << 4;
+         if (op & 0x08)
+           aecb.data |= 1 << 14;
+         aecb.cmd = ARM_EXIDX_CMD_REG_POP;
+       }
+      else if (op == ARM_EXTBL_OP_FINISH)
+       {
+         aecb.cmd = ARM_EXIDX_CMD_FINISH;
+         buf = end;
+       }
+      else if (op == 0xb1)
+       {
+         uint8_t op2 = READ_OP ();
+         if (op2 == 0 || (op2 & 0xf0))
+           aecb.cmd = ARM_EXIDX_CMD_RESERVED;
+         else
+           {
+             aecb.cmd = ARM_EXIDX_CMD_REG_POP;
+             aecb.data = op2 & 0x0f;
+           }
+       }
+      else if (op == 0xb2)
+       {
+         uint32_t offset = 0;
+         uint8_t byte, shift = 0;
+         do
+           {
+             byte = READ_OP ();
+             offset |= (byte & 0x7f) << shift;
+             shift += 7;
+           }
+         while (byte & 0x80);
+         aecb.data = offset * 4 + 0x204;
+         aecb.cmd = ARM_EXIDX_CMD_DATA_POP;
+       }
+      else if (op == 0xb3 || op == 0xc8 || op == 0xc9)
+       {
+         aecb.cmd = ARM_EXIDX_CMD_VFP_POP;
+         aecb.data = READ_OP ();
+         if (op == 0xc8)
+           aecb.data |= ARM_EXIDX_VFP_SHIFT_16;
+         if (op != 0xb3)
+           aecb.data |= ARM_EXIDX_VFP_DOUBLE;
+       }
+      else if ((op & 0xf8) == 0xb8 || (op & 0xf8) == 0xd0)
+       {
+         aecb.cmd = ARM_EXIDX_CMD_VFP_POP;
+         aecb.data = 0x80 | (op & 0x07);
+         if ((op & 0xf8) == 0xd0)
+           aecb.data |= ARM_EXIDX_VFP_DOUBLE;
+       }
+      else if (op >= 0xc0 && op <= 0xc5)
+       {
+         aecb.cmd = ARM_EXIDX_CMD_WREG_POP;
+         aecb.data = 0xa0 | (op & 0x07);
+       }
+      else if (op == 0xc6)
+       {
+         aecb.cmd = ARM_EXIDX_CMD_WREG_POP;
+         aecb.data = READ_OP ();
+       }
+      else if (op == 0xc7)
+       {
+         uint8_t op2 = READ_OP ();
+         if (op2 == 0 || (op2 & 0xf0))
+           aecb.cmd = ARM_EXIDX_CMD_RESERVED;
+         else
+           {
+             aecb.cmd = ARM_EXIDX_CMD_WCGR_POP;
+             aecb.data = op2 & 0x0f;
+           }
+       }
+      else
+       aecb.cmd = ARM_EXIDX_CMD_RESERVED;
+
+      ret = (*cb) (&aecb);
+      if (ret < 0)
+       return ret;
+    }
+  return 0;
+}
+
+static inline uint32_t
+prel31_read (uint32_t prel31)
+{
+  return ((int32_t)prel31 << 1) >> 1;
+}
+
+/**
+ * Finds the index of the table entry for the given address
+ * using a binary search.
+ * @returns The table index (or -1 if not found).
+ */
+HIDDEN int
+arm_exidx_lookup (uint32_t *exidx_data, uint32_t exidx_size, uint32_t ip)
+{
+  unsigned lo = 0, hi = exidx_size / 8;
+  while (lo < hi)
+    {
+      unsigned mid = (lo + hi) / 2;
+      uint32_t base = (uint32_t)(exidx_data + mid * 2);
+      uint32_t addr = base + prel31_read (exidx_data[mid * 2]);
+      if (ip < addr)
+       hi = mid;
+      else
+       lo = mid + 1;
+    }
+  return hi - 1;
+}
+
+HIDDEN int
+arm_exidx_entry_lookup (struct elf_image *ei,
+               Elf_W (Shdr) *exidx, uint32_t ip)
+{
+#if 1
+  return arm_exidx_lookup (ei->image + exidx->sh_offset, exidx->sh_size, ip);
+#else
+  unsigned n_entries = exidx->sh_size / 8;
+  uint32_t *exidx_data = ei->image + exidx->sh_offset;
+  unsigned lo = 0, hi = n_entries;
+
+  while (lo < hi)
+    {
+      unsigned mid = (lo + hi) / 2;
+      uint32_t base = exidx->sh_addr + mid * 8;
+      uint32_t addr = base + prel31_read (exidx_data[mid * 2]);
+      if (ip < addr)
+       hi = mid;
+      else
+       lo = mid + 1;
+    }
+  return hi - 1;
+#endif
+}
+
+HIDDEN int
+arm_exidx_extract (struct arm_exidx_entry *entry, uint8_t *buf)
+{
+  int nbuf = 0;
+  uint32_t *addr = prel31_to_addr (&entry->addr);
+
+  uint32_t data = entry->data;
+  if (data == ARM_EXIDX_CANT_UNWIND)
+    {
+      Debug (2, "0x1 [can't unwind]\n");
+      nbuf = -UNW_ESTOPUNWIND;
+    }
+  else if (data & ARM_EXIDX_COMPACT)
+    {
+      Debug (2, "%p compact model %d [%8.8x]\n", addr, (data >> 24) & 0x7f, 
data);
+      buf[nbuf++] = data >> 16;
+      buf[nbuf++] = data >> 8;
+      buf[nbuf++] = data;
+    }
+  else
+    {
+      uint32_t *extbl_data = prel31_to_addr (&entry->data);
+      data = extbl_data[0];
+      unsigned int n_table_words = 0;
+      if (data & ARM_EXIDX_COMPACT)
+       {
+         int pers = (data >> 24) & 0x0f;
+         Debug (2, "%p compact model %d [%8.8x]\n", addr, pers, data);
+         if (pers == 1 || pers == 2)
+           {
+             n_table_words = (data >> 16) & 0xff;
+             extbl_data += 1;
+           }
+         else
+           buf[nbuf++] = data >> 16;
+         buf[nbuf++] = data >> 8;
+         buf[nbuf++] = data;
+       }
+      else
+       {
+         void *pers = prel31_to_addr (extbl_data);
+         Debug (2, "%p Personality routine: %8.8x\n", addr, pers);
+         n_table_words = extbl_data[1] >> 24;
+         buf[nbuf++] = extbl_data[1] >> 16;
+         buf[nbuf++] = extbl_data[1] >> 8;
+         buf[nbuf++] = extbl_data[1];
+         extbl_data += 2;
+       }
+      assert (n_table_words <= 5);
+      unsigned j;
+      for (j = 0; j < n_table_words; j++)
+       {
+         data = *extbl_data++;
+         buf[nbuf++] = data >> 24;
+         buf[nbuf++] = data >> 16;
+         buf[nbuf++] = data >> 8;
+         buf[nbuf++] = data >> 0;
+       }
+    }
+
+  if (nbuf > 0 && buf[nbuf - 1] != ARM_EXTBL_OP_FINISH)
+    buf[nbuf++] = ARM_EXTBL_OP_FINISH;
+
+  return nbuf;
+}
+
+HIDDEN int
+arm_exidx_entry_extract (struct elf_image *ei,
+               Elf_W (Shdr) *exidx, Elf_W (Shdr) *extbl,
+               unsigned i, uint8_t *buf)
+{
+  int nbuf = 0;
+  uint32_t *exidx_data = ei->image + exidx->sh_offset;
+  uint32_t base = exidx->sh_addr + i * 8;
+  uint32_t one = base + prel31_read (exidx_data[i * 2]);
+
+  uint32_t two = exidx_data[i * 2 + 1];
+  if (two == ARM_EXIDX_CANT_UNWIND)
+    printf ("0x1 [can't unwind]\n");
+  else if (two & ARM_EXIDX_COMPACT)
+    {
+      printf ("compact model %d [%8.8x]\n", (two >> 24) & 0x7f, two);
+      buf[nbuf++] = two >> 16;
+      buf[nbuf++] = two >> 8;
+      buf[nbuf++] = two;
+    }
+  else
+    {
+      assert (NULL != extbl);
+      two = base + prel31_read (two) + 4;
+      uint32_t *extbl_data = ei->image + extbl->sh_offset
+             + (two - extbl->sh_addr);
+      two = extbl_data[0];
+      unsigned int n_table_words = 0;
+      if (two & ARM_EXIDX_COMPACT)
+       {
+         int pers = (two >> 24) & 0x0f;
+         printf ("compact model %d [%8.8x]\n", pers, two);
+         if (pers == 1 || pers == 2)
+           {
+             n_table_words = (two >> 16) & 0xff;
+             extbl_data += 1;
+           }
+         else
+           buf[nbuf++] = two >> 16;
+         buf[nbuf++] = two >> 8;
+         buf[nbuf++] = two;
+       }
+      else
+       {
+         uint32_t pers = prel31_read (extbl_data[0]);
+         pers += extbl->sh_addr + i * 8 + 4;
+         printf ("Personality routine: %8.8x\n", pers);
+         n_table_words = extbl_data[1] >> 24;
+         buf[nbuf++] = extbl_data[1] >> 16;
+         buf[nbuf++] = extbl_data[1] >> 8;
+         buf[nbuf++] = extbl_data[1];
+         extbl_data += 2;
+       }
+      assert (n_table_words <= 5);
+      unsigned j;
+      for (j = 0; j < n_table_words; j++)
+       {
+         two = *extbl_data++;
+         buf[nbuf++] = two >> 24;
+         buf[nbuf++] = two >> 16;
+         buf[nbuf++] = two >> 8;
+         buf[nbuf++] = two >> 0;
+       }
+    }
+
+  if (nbuf > 0 && buf[nbuf - 1] != ARM_EXTBL_OP_FINISH)
+    buf[nbuf++] = ARM_EXTBL_OP_FINISH;
+
+  return nbuf;
+}
+
+HIDDEN void
+arm_exidx_section_find (struct elf_image *ei,
+               Elf_W (Shdr) **exidx, Elf_W (Shdr) **extbl)
+{
+  Elf_W (Ehdr) *ehdr = ei->image;
+  Elf_W (Shdr) *shdr;
+  shdr = (Elf_W (Shdr) *)((char *)ei->image + ehdr->e_shoff);
+  char *names = (char *)ei->image + shdr[ehdr->e_shstrndx].sh_offset;
+  int i = 0;
+  for (i = 0; i < ehdr->e_shnum; i++)
+    {
+      char *name = names + shdr[i].sh_name;
+      switch (shdr[i].sh_type)
+       {
+         case SHT_ARM_EXIDX:
+           *exidx = shdr + i;
+           break;
+         case SHT_PROGBITS:
+           if (strcmp (name, ".ARM.extab") != 0)
+             break;
+           *extbl = shdr + i;
+           break;
+       }
+    }
+}
+
+/**
+ * Callback to dl_iterate_phr to find each library's unwind table.
+ * If found, calls arm_exidx_table_add to remember it for later lookups.
+ */
+static int
+arm_exidx_init_local_cb (struct dl_phdr_info *info, size_t size, void *data)
+{
+  unsigned i;
+
+  for (i = 0; i < info->dlpi_phnum; i++)
+    {
+      const ElfW (Phdr) *phdr = info->dlpi_phdr + i;
+      if (phdr->p_type != PT_ARM_EXIDX)
+       continue;
+
+      const char *name = info->dlpi_name;
+      if (NULL == name || 0 == name[0])
+       name = arm_exidx_appname;
+
+      ElfW (Addr) addr = info->dlpi_addr + phdr->p_vaddr;
+      ElfW (Word) size = phdr->p_filesz;
+
+      arm_exidx_table_add (name,
+         (struct arm_exidx_entry *)addr,
+         (struct arm_exidx_entry *)(addr + size));
+      break;
+    }
+  return 0;
+}
+
+/**
+ * Must be called for local process lookups.
+ */
+HIDDEN int
+arm_exidx_init_local (const char *appname)
+{
+  arm_exidx_appname = appname;
+  // traverse all libraries and find unwind tables
+  arm_exidx_table_reset_all();
+  return dl_iterate_phdr (&arm_exidx_init_local_cb, NULL);
+}
diff --git a/src/elfxx.h b/src/elfxx.h
index e316970..a85cc68 100644
--- a/src/elfxx.h
+++ b/src/elfxx.h
@@ -31,8 +31,6 @@ WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE 
SOFTWARE.  */
 #include <sys/mman.h>
 #include <sys/stat.h>
 
-#include "libunwind_i.h"
-
 #if ELF_CLASS == ELFCLASS32
 # define ELF_W(x)      ELF32_##x
 # define Elf_W(x)      Elf32_##x
@@ -43,6 +41,8 @@ WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE 
SOFTWARE.  */
 # define elf_w(x)      _Uelf64_##x
 #endif
 
+#include "libunwind_i.h"
+
 extern int elf_w (valid_object) (struct elf_image *ei);
 extern int elf_w (get_proc_name) (unw_addr_space_t as,
                                  pid_t pid, unw_word_t ip,
-- 
1.7.4.1