[PATCH] PowerPC: use libgcc _Unwind functions to get backtrace

[Adhemerval Zanella]

This patch changes the way backtraces are obtained on PowerPC by
relaying on libgcc _Unwind function instead of just backchain parse.
It fixes debug/tst-backtrace5 for PPC32 and PPC64.

Tested on PPC32 and PPC64.

---

2013-07-17  Adhemerval Zanella  <azanella@linux.vnet.ibm.com>

        * sysdeps/powerpc/Makefile: Add -funwind-tables to backtrace.c.
	* sysdeps/powerpc/backtrace.c: New file: common PowerPC backtrace
	code.
	* sysdeps/powerpc/powerpc32/backtrace.c (__backtrace): Rename to
	__backchain_backtrace and define it only for shared builds.
	* sysdeps/powerpc/powerpc64/backtrace.c (__backtrace): Likewise.

--

diff --git a/sysdeps/powerpc/Makefile b/sysdeps/powerpc/Makefile
index f75e625..53fa8fb 100644
--- a/sysdeps/powerpc/Makefile
+++ b/sysdeps/powerpc/Makefile
@@ -2,6 +2,10 @@ ifeq ($(subdir),string)
 CFLAGS-memcmp.c += -Wno-uninitialized
 endif
 
+ifeq ($(subdir),debug)
+CFLAGS-backtrace.c += -funwind-tables
+endif
+
 ifeq ($(subdir),elf)
 # extra shared linker files to link into dl-allobjs.so and libc
 sysdep-dl-routines += dl-machine
diff --git a/sysdeps/powerpc/backtrace.c b/sysdeps/powerpc/backtrace.c
new file mode 100644
index 0000000..06f41e1
--- /dev/null
+++ b/sysdeps/powerpc/backtrace.c
@@ -0,0 +1,129 @@
+/* Return backtrace of current program state.
+   Copyright (C) 2013 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Library General Public License as
+   published by the Free Software Foundation; either version 2 of the
+   License, or (at your option) any later version.
+
+   The GNU C Library 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
+   Library General Public License for more details.
+
+   You should have received a copy of the GNU Library General Public
+   License along with the GNU C Library; see the file COPYING.LIB.  If
+   not, see <http://www.gnu.org/licenses/>.  */
+
+#include <execinfo.h>
+#include <dlfcn.h>
+#include <stddef.h>
+#include <unwind.h>
+
+
+struct trace_arg
+{
+  void **array;
+  _Unwind_Word cfa;
+  int cnt;
+  int size;
+};
+
+#ifdef SHARED
+static _Unwind_Reason_Code (*unwind_backtrace) (_Unwind_Trace_Fn, void *);
+static _Unwind_Ptr (*unwind_getip) (struct _Unwind_Context *);
+static _Unwind_Word (*unwind_getcfa) (struct _Unwind_Context *);
+static void *libgcc_handle;
+
+/* Dummy version in case libgcc_s does not contain the real code.  */
+static _Unwind_Word
+dummy_getcfa (struct _Unwind_Context *ctx __attribute__ ((unused)))
+{
+  return 0;
+}
+
+static void
+init (void)
+{
+  libgcc_handle = __libc_dlopen ("libgcc_s.so.1");
+
+  if (libgcc_handle == NULL)
+    return;
+
+  unwind_backtrace = __libc_dlsym (libgcc_handle, "_Unwind_Backtrace");
+  unwind_getip = __libc_dlsym (libgcc_handle, "_Unwind_GetIP");
+  if (unwind_getip == NULL)
+    unwind_backtrace = NULL;
+  unwind_getcfa = (__libc_dlsym (libgcc_handle, "_Unwind_GetCFA")
+		  ?: dummy_getcfa);
+}
+
+#else
+# define unwind_backtrace _Unwind_Backtrace
+# define unwind_getip     _Unwind_GetIP
+# define unwind_getcfa    _Unwind_GetCFA
+#endif
+
+static _Unwind_Reason_Code
+backtrace_helper (struct _Unwind_Context *ctx, void *a)
+{
+  struct trace_arg *arg = a;
+
+  /* We are first called with address in the __backtrace function.
+     Skip it.  */
+  if (arg->cnt != -1)
+    {
+      arg->array[arg->cnt] = (void *) unwind_getip (ctx);
+
+      /* Check whether we make any progress.  */
+      _Unwind_Word cfa = unwind_getcfa (ctx);
+
+      if (arg->cnt > 0 && arg->array[arg->cnt - 1] == arg->array[arg->cnt]
+	 && cfa == arg->cfa)
+       return _URC_END_OF_STACK;
+      arg->cfa = cfa;
+    }
+  if (++arg->cnt == arg->size)
+    return _URC_END_OF_STACK;
+  return _URC_NO_REASON;
+}
+
+
+int
+__backtrace (void **array, int size)
+{
+  struct trace_arg arg = { .array = array, .cfa = 0, .size = size, .cnt = -1 };
+#ifdef SHARED
+  __libc_once_define (static, once);
+  __libc_once (once, init);
+
+  if (unwind_backtrace == NULL)
+    return __backchain_backtrace (array, size);
+#endif
+
+  if (size >= 1)
+    unwind_backtrace (backtrace_helper, &arg);
+
+  /* _Unwind_Backtrace seems to put NULL address above
+     _start.  Fix it up here.  */
+  if (arg.cnt > 1 && arg.array[arg.cnt - 1] == NULL)
+    --arg.cnt;
+  return arg.cnt != -1 ? arg.cnt : 0;
+}
+weak_alias (__backtrace, backtrace)
+libc_hidden_def (__backtrace)
+
+
+#ifdef SHARED
+/* Free all resources if necessary.  */
+libc_freeres_fn (free_mem)
+{
+  unwind_backtrace = NULL;
+  if (libgcc_handle != NULL)
+    {
+      __libc_dlclose (libgcc_handle);
+      libgcc_handle = NULL;
+    }
+}
+#endif
diff --git a/sysdeps/powerpc/powerpc32/backtrace.c b/sysdeps/powerpc/powerpc32/backtrace.c
index b4b11dd..ce70d8d 100644
--- a/sysdeps/powerpc/powerpc32/backtrace.c
+++ b/sysdeps/powerpc/powerpc32/backtrace.c
@@ -19,6 +19,8 @@
 #include <execinfo.h>
 #include <stddef.h>
 
+#ifdef SHARED
+
 /* This is the stack layout we see with every stack frame.
    Note that every routine is required by the ABI to lay out the stack
    like this.
@@ -35,8 +37,8 @@ struct layout
   void *return_address;
 };
 
-int
-__backtrace (void **array, int size)
+static int
+__backchain_backtrace (void **array, int size)
 {
   struct layout *current;
   int count;
@@ -60,5 +62,6 @@ __backtrace (void **array, int size)
 
   return count;
 }
-weak_alias (__backtrace, backtrace)
-libc_hidden_def (__backtrace)
+#endif
+
+#include <sysdeps/powerpc/backtrace.c>
diff --git a/sysdeps/powerpc/powerpc64/backtrace.c b/sysdeps/powerpc/powerpc64/backtrace.c
index 2d3e051..4043ab4 100644
--- a/sysdeps/powerpc/powerpc64/backtrace.c
+++ b/sysdeps/powerpc/powerpc64/backtrace.c
@@ -19,6 +19,8 @@
 #include <execinfo.h>
 #include <stddef.h>
 
+#ifdef SHARED
+
 /* This is the stack layout we see with every stack frame.
    Note that every routine is required by the ABI to lay out the stack
    like this.
@@ -31,6 +33,7 @@
             | (unused)       |        | return address  |
             +----------------+        +-----------------+
 */
+
 struct layout
 {
   struct layout *next;
@@ -38,8 +41,8 @@ struct layout
   void *return_address;
 };
 
-int
-__backtrace (void **array, int size)
+static int
+__backchain_backtrace (void **array, int size)
 {
   struct layout *current;
   int count;
@@ -63,5 +66,6 @@ __backtrace (void **array, int size)
 
   return count;
 }
-weak_alias (__backtrace, backtrace)
-libc_hidden_def (__backtrace)
+#endif
+
+#include <sysdeps/powerpc/backtrace.c>