[Libunwind-devel] [PATCH 4/4] ARM: Initial support for remote unwinding using libunwind-ptrace

[Ken Werner]

Change _UPTi_find_unwind_table to also look for the ARM specific unwind
information. Adjust the ARM unwind code to read memory using the accessor
routines.

Signed-off-by: Ken Werner <address@hidden>
---
 include/libunwind-arm.h          |    5 --
 include/tdep-arm/ex_tables.h     |    2 +-
 src/arm/Gex_tables.c             |  142 +++++++++++++++++++++++++++-----------
 src/arm/Gstep.c                  |    4 +-
 src/ptrace/_UPT_find_proc_info.c |   45 ++++++++++++-
 src/ptrace/_UPT_internal.h       |    3 +
 6 files changed, 150 insertions(+), 51 deletions(-)

diff --git a/include/libunwind-arm.h b/include/libunwind-arm.h
index 211ae50..492331e 100644
--- a/include/libunwind-arm.h
+++ b/include/libunwind-arm.h
@@ -280,11 +280,6 @@ typedef ucontext_t unw_tdep_context_t;
 
 #include "libunwind-dynamic.h"
 
-struct arm_exidx_entry {
-  uint32_t addr;
-  uint32_t data;
-};
-
 typedef struct
   {
     /* no arm-specific auxiliary proc-info */
diff --git a/include/tdep-arm/ex_tables.h b/include/tdep-arm/ex_tables.h
index 6ea3414..8906f13 100644
--- a/include/tdep-arm/ex_tables.h
+++ b/include/tdep-arm/ex_tables.h
@@ -48,7 +48,7 @@ struct arm_exbuf_data
 #define arm_exidx_decode       UNW_OBJ(arm_exidx_decode)
 #define arm_exidx_apply_cmd    UNW_OBJ(arm_exidx_apply_cmd)
 
-int arm_exidx_extract (struct arm_exidx_entry *entry, uint8_t *buf);
+int arm_exidx_extract (struct dwarf_cursor *c, uint8_t *buf);
 int arm_exidx_decode (const uint8_t *buf, uint8_t len, struct dwarf_cursor *c);
 int arm_exidx_apply_cmd (struct arm_exbuf_data *edata, struct dwarf_cursor *c);
 
diff --git a/src/arm/Gex_tables.c b/src/arm/Gex_tables.c
index fc18088..e6ac3ef 100644
--- a/src/arm/Gex_tables.c
+++ b/src/arm/Gex_tables.c
@@ -22,6 +22,12 @@ 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.  */
 
+/* This file contains functionality for parsing and interpreting the ARM
+specific unwind information.  Documentation about the exception handling
+ABI for the ARM architecture can be found at:
+http://infocenter.arm.com/help/topic/com.arm.doc.ihi0038a/IHI0038A_ehabi.pdf
+*/ 
+
 #include "libunwind_i.h"
 
 #define ARM_EXBUF_START(x)     (((x) >> 4) & 0x0f)
@@ -53,11 +59,19 @@ prel31_read (uint32_t prel31)
   return ((int32_t)prel31 << 1) >> 1;
 }
 
-static inline uint32_t
-prel31_to_addr (uint32_t *addr)
+static inline int
+prel31_to_addr (unw_addr_space_t as, void *arg, unw_word_t prel31,
+               unw_word_t *val)
 {
-  uint32_t offset = ((long)*addr << 1) >> 1;
-  return (uint32_t)addr + offset;
+  unw_word_t offset;
+
+  if ((*as->acc.access_mem)(as, prel31, &offset, 0, arg) < 0)
+    return -UNW_EINVAL;
+
+  offset = ((long)offset << 1) >> 1;
+  *val = prel31 + offset;
+
+  return 0;
 }
 
 /**
@@ -267,17 +281,31 @@ arm_exidx_decode (const uint8_t *buf, uint8_t len, struct 
dwarf_cursor *c)
 }
 
 /**
- * Reads the given entry and extracts the unwind instructions into buf.
- * Returns the number of the extracted unwind insns or -UNW_ESTOPUNWIND
- * if the special bit pattern ARM_EXIDX_CANT_UNWIND (0x1) was found.
+ * Reads the entry from the given cursor and extracts the unwind instructions
+ * into buf.  Returns the number of the extracted unwind insns or 
+ * -UNW_ESTOPUNWIND if the special bit pattern ARM_EXIDX_CANT_UNWIND (0x1) was
+ * found.
  */
 HIDDEN int
-arm_exidx_extract (struct arm_exidx_entry *entry, uint8_t *buf)
+arm_exidx_extract (struct dwarf_cursor *c, uint8_t *buf)
 {
   int nbuf = 0;
-  unw_word_t addr = prel31_to_addr (&entry->addr);
+  unw_word_t entry = (unw_word_t) c->pi.unwind_info;
+  unw_word_t addr;
+  uint32_t data;
+
+  /* An ARM unwind entry consists of a prel31 offset to the start of a
+     function followed by 31bits of data: 
+       * if set to 0x1: the function cannot be unwound (EXIDX_CANTUNWIND)
+       * if bit 31 is one: this is a table entry itself (ARM_EXIDX_COMPACT)
+       * if bit 31 is zero: this is a prel31 offset of the start of the
+        table entry for this function  */
+  if (prel31_to_addr(c->as, c->as_arg, entry, &addr) < 0)
+    return -UNW_EINVAL;
+
+  if ((*c->as->acc.access_mem)(c->as, entry + 4, &data, 0, c->as_arg) < 0)
+    return -UNW_EINVAL;
 
-  uint32_t data = entry->data;
   if (data == ARM_EXIDX_CANT_UNWIND)
     {
       Debug (2, "0x1 [can't unwind]\n");
@@ -285,16 +313,23 @@ arm_exidx_extract (struct arm_exidx_entry *entry, uint8_t 
*buf)
     }
   else if (data & ARM_EXIDX_COMPACT)
     {
-      Debug (2, "%p compact model %d [%8.8x]\n", (void *)addr, (data >> 24) & 
0x7f, data);
+      Debug (2, "%p compact model %d [%8.8x]\n", (void *)addr,
+            (data >> 24) & 0x7f, data);
       buf[nbuf++] = data >> 16;
       buf[nbuf++] = data >> 8;
       buf[nbuf++] = data;
     }
   else
     {
-      uint32_t *extbl_data = (uint32_t *)prel31_to_addr (&entry->data);
-      data = (unw_word_t)extbl_data[0];
+      unw_word_t extbl_data;
       unsigned int n_table_words = 0;
+
+      if (prel31_to_addr(c->as, c->as_arg, entry + 4, &extbl_data) < 0)
+        return -UNW_EINVAL;
+
+      if ((*c->as->acc.access_mem)(c->as, extbl_data, &data, 0, c->as_arg) < 0)
+       return -UNW_EINVAL;
+
       if (data & ARM_EXIDX_COMPACT)
        {
          int pers = (data >> 24) & 0x0f;
@@ -302,7 +337,7 @@ arm_exidx_extract (struct arm_exidx_entry *entry, uint8_t 
*buf)
          if (pers == 1 || pers == 2)
            {
              n_table_words = (data >> 16) & 0xff;
-             extbl_data += 1;
+             extbl_data += 4;
            }
          else
            buf[nbuf++] = data >> 16;
@@ -311,19 +346,28 @@ arm_exidx_extract (struct arm_exidx_entry *entry, uint8_t 
*buf)
        }
       else
        {
-         unw_word_t pers = prel31_to_addr (extbl_data);
-         Debug (2, "%p Personality routine: %8p\n", (void *)addr, (void 
*)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;
+         unw_word_t pers;
+         if (prel31_to_addr (c->as, c->as_arg, extbl_data, &pers) < 0)
+           return -UNW_EINVAL;
+         Debug (2, "%p Personality routine: %8p\n", (void *)addr,
+                (void *)pers);
+         if ((*c->as->acc.access_mem)(c->as, extbl_data + 4, &data, 0,
+                                      c->as_arg) < 0)
+           return -UNW_EINVAL;
+         n_table_words = data >> 24;
+         buf[nbuf++] = data >> 16;
+         buf[nbuf++] = data >> 8;
+         buf[nbuf++] = data;
+         extbl_data += 8;
        }
       assert (n_table_words <= 5);
       unsigned j;
       for (j = 0; j < n_table_words; j++)
        {
-         data = *extbl_data++;
+         if ((*c->as->acc.access_mem)(c->as, extbl_data, &data, 0,
+                                      c->as_arg) < 0)
+           return -UNW_EINVAL;
+         extbl_data += 4;
          buf[nbuf++] = data >> 24;
          buf[nbuf++] = data >> 16;
          buf[nbuf++] = data >> 8;
@@ -345,41 +389,59 @@ tdep_search_unwind_table (unw_addr_space_t as, unw_word_t 
ip,
   if (UNW_TRY_METHOD (UNW_ARM_METHOD_EXIDX)
       && di->format == UNW_INFO_FORMAT_ARM_EXIDX)
     {
-      struct arm_exidx_entry *first =
-       (struct arm_exidx_entry *) di->u.rti.table_data;
-      struct arm_exidx_entry *last =
-       ((struct arm_exidx_entry *) (di->u.rti.table_data +
-                                    di->u.rti.table_len)) - 1;
-      struct arm_exidx_entry *entry;
-
-      if (ip < prel31_to_addr (&first->addr))
+      /* The .ARM.exidx section contains a sorted list of key-value pairs -
+        the unwind entries.  The 'key' is a prel31 offset to the start of a
+        function.  We binary search this section in order to find the
+        appropriate unwind entry.  */
+      unw_word_t first = di->u.rti.table_data;
+      unw_word_t last = di->u.rti.table_data + di->u.rti.table_len - 8;
+      unw_word_t entry, val;
+
+      if (prel31_to_addr (as, arg, first, &val) < 0 && ip < val)
        return -UNW_ENOINFO;
-      else if (ip >= prel31_to_addr (&last->addr))
+
+      if (prel31_to_addr (as, arg, last, &val) < 0)
+       return -UNW_EINVAL;
+
+      if (ip >= val)
        {
-          entry = last;
-          pi->start_ip = prel31_to_addr (&last->addr);
-          pi->end_ip = di->end_ip - 1;
+         entry = last;
+
+         if (prel31_to_addr (as, arg, last, &pi->start_ip) < 0)
+           return -UNW_EINVAL;
+
+         pi->end_ip = di->end_ip -1;
        }
       else
        {
-         while (first < last - 1)
+         while (first < last - 8)
            {
-             entry = first + ((last - first + 1) >> 1);
-             if (ip < prel31_to_addr (&entry->addr))
+             entry = first + (((last - first) / 8 + 1) >> 1) * 8;
+
+             if (prel31_to_addr (as, arg, entry, &val) < 0)
+               return -UNW_EINVAL;
+
+             if (ip < val)
                last = entry;
              else
                first = entry;
            }
 
          entry = first;
-         pi->start_ip = prel31_to_addr (&entry->addr);
-         pi->end_ip = prel31_to_addr (&(entry + 1)->addr) - 1;
+
+         if (prel31_to_addr (as, arg, entry, &pi->start_ip) < 0)
+           return -UNW_EINVAL;
+
+         if (prel31_to_addr (as, arg, entry + 8, &pi->end_ip) < 0)
+           return -UNW_EINVAL;
+
+         pi->end_ip--;
        }
 
       if (need_unwind_info)
        {
          pi->unwind_info_size = 8;
-         pi->unwind_info = entry;
+         pi->unwind_info = (void *) entry;
          pi->format = UNW_INFO_FORMAT_ARM_EXIDX;
        }
       return 0;
diff --git a/src/arm/Gstep.c b/src/arm/Gstep.c
index 60cbf2c..270058b 100644
--- a/src/arm/Gstep.c
+++ b/src/arm/Gstep.c
@@ -35,7 +35,6 @@ static inline int
 arm_exidx_step (struct cursor *c)
 {
   unw_word_t old_ip, old_cfa;
-  struct arm_exidx_entry *entry;
   uint8_t buf[32];
   int ret;
 
@@ -51,8 +50,7 @@ arm_exidx_step (struct cursor *c)
   if (c->dwarf.pi.format != UNW_INFO_FORMAT_ARM_EXIDX)
     return -UNW_ENOINFO;
 
-  entry = (struct arm_exidx_entry *)c->dwarf.pi.unwind_info;
-  ret = arm_exidx_extract (entry, buf);
+  ret = arm_exidx_extract (&c->dwarf, buf);
   if (ret < 0)
     return ret;
 
diff --git a/src/ptrace/_UPT_find_proc_info.c b/src/ptrace/_UPT_find_proc_info.c
index e98a344..44feb34 100644
--- a/src/ptrace/_UPT_find_proc_info.c
+++ b/src/ptrace/_UPT_find_proc_info.c
@@ -176,6 +176,9 @@ _UPTi_find_unwind_table (struct UPT_info *ui, 
unw_addr_space_t as,
   unw_proc_info_t pi;
   unw_accessors_t *a;
   Elf_W(Ehdr) *ehdr;
+#if UNW_TARGET_ARM
+  const Elf_W(Phdr) *parm_exidx = NULL;
+#endif
   int i, ret, found = 0;
 
   /* XXX: Much of this code is Linux/LSB-specific.  */
@@ -205,6 +208,12 @@ _UPTi_find_unwind_table (struct UPT_info *ui, 
unw_addr_space_t as,
          pdyn = phdr + i;
          break;
 
+#if UNW_TARGET_ARM
+       case PT_ARM_EXIDX:
+         parm_exidx = phdr + i;
+         break;
+#endif
+
        default:
          break;
        }
@@ -316,6 +325,20 @@ _UPTi_find_unwind_table (struct UPT_info *ui, 
unw_addr_space_t as,
       found = 1;
     }
 
+#if UNW_TARGET_ARM
+  if (parm_exidx)
+    {
+      ui->di_arm.format = UNW_INFO_FORMAT_ARM_EXIDX;
+      ui->di_arm.start_ip = segbase;
+      ui->di_arm.end_ip = ui->di_arm.start_ip + ptxt->p_memsz;
+      ui->di_arm.u.rti.name_ptr = (unw_word_t) path;
+      ui->di_arm.u.rti.table_data = parm_exidx->p_vaddr + segbase -
+                                   ptxt->p_vaddr;
+      ui->di_arm.u.rti.table_len = parm_exidx->p_memsz;
+      found = 1;
+    }
+#endif
+
 #ifdef CONFIG_DEBUG_FRAME
   {
       /* Try .debug_frame. */
@@ -362,6 +385,10 @@ get_unwind_info (struct UPT_info *ui, unw_addr_space_t as, 
unw_word_t ip)
 
   if ((ui->di_cache.format != -1
        && ip >= ui->di_cache.start_ip && ip < ui->di_cache.end_ip)
+#if UNW_TARGET_ARM
+      || (ui->di_debug.format != -1
+       && ip >= ui->di_arm.start_ip && ip < ui->di_arm.end_ip)
+#endif
       || (ui->di_debug.format != -1
        && ip >= ui->di_debug.start_ip && ip < ui->di_debug.end_ip))
     return 0;
@@ -377,6 +404,10 @@ get_unwind_info (struct UPT_info *ui, unw_addr_space_t as, 
unw_word_t ip)
       ui->di_debug.start_ip = ui->di_debug.end_ip = 0;
       ui->di_cache.format = -1;
       ui->di_debug.format = -1;
+#if UNW_TARGET_ARM
+      ui->di_arm.start_ip = ui->di_arm.end_ip = 0;
+      ui->di_arm.format = -1;
+#endif
     }
 
   if (tdep_get_elf_image (&ui->ei, ui->pid, ip, &segbase, &mapoff, path,
@@ -400,7 +431,11 @@ get_unwind_info (struct UPT_info *ui, unw_addr_space_t as, 
unw_word_t ip)
       && (ip < ui->di_debug.start_ip || ip >= ui->di_debug.end_ip))
      ui->di_debug.format = -1;
 
-  if (ui->di_cache.format == -1 && ui->di_debug.format == -1)
+  if (ui->di_cache.format == -1
+#if UNW_TARGET_ARM
+      && ui->di_arm.format == -1
+#endif
+      && ui->di_debug.format == -1)
     return -UNW_ENOINFO;
 
   return 0;
@@ -444,10 +479,16 @@ _UPT_find_proc_info (unw_addr_space_t as, unw_word_t ip, 
unw_proc_info_t *pi,
     }
 #endif
 
-  if (ret == -UNW_ENOINFO && ui->di_cache.format == -1)
+  if (ret == -UNW_ENOINFO && ui->di_cache.format != -1)
     ret = tdep_search_unwind_table (as, ip, &ui->di_cache,
                                    pi, need_unwind_info, arg);
 
+#if UNW_TARGET_ARM
+  if (ret == -UNW_ENOINFO && ui->di_arm.format != -1)
+    ret = tdep_search_unwind_table (as, ip, &ui->di_arm, pi,
+                                    need_unwind_info, arg);
+#endif
+
   if (ret == -UNW_ENOINFO && ui->di_debug.format != -1)
     ret = tdep_search_unwind_table (as, ip, &ui->di_debug, pi,
                                    need_unwind_info, arg);
diff --git a/src/ptrace/_UPT_internal.h b/src/ptrace/_UPT_internal.h
index 54d5fc9..a7a0481 100644
--- a/src/ptrace/_UPT_internal.h
+++ b/src/ptrace/_UPT_internal.h
@@ -57,6 +57,9 @@ struct UPT_info
 #if UNW_TARGET_IA64
     unw_dyn_info_t ktab;
 #endif
+#if UNW_TARGET_ARM
+    unw_dyn_info_t di_arm;     /* additional table info for .ARM.exidx */
+#endif
   };
 
 extern int _UPT_reg_offset[UNW_REG_LAST + 1];
-- 
1.7.4.1