[PATCH] i386 backtrace () using _Unwind_Backtrace

[Jakub Jelinek <jakub at redhat dot com>]

Hi!

_Unwind_Backtrace with contemporary libraries (i.e. those that have
PT_GNU_EH_FRAME program header and .eh_frame_hdr binary search table)
doesn't use malloc, so I think it is safe to use it for backtrace ().

2004-10-22  Jakub Jelinek  <jakub@redhat.com>

	* sysdeps/i386/Makefile (CFLAGS-backtrace.c): Add -fexceptions.
	* sysdeps/i386/backtrace.c: Include <bits/libc-lock.h>, <dlfcn.h>,
	<stdlib.h> and <unwind.h>.  Remove <bp-checks.h> include.
	(struct trace_arg): New type.
	(unwind_backtrace, unwind_getip, unwind_getcfa, unwind_getgr): New
	fn pointers resp. macros.
	(init, backtrace_helper): New functions.
	(__backtrace): Rewritten to use _Unwind_Backtrace first and fall
	back to frame pointer walking.

--- libc/sysdeps/i386/Makefile.jj	2003-09-17 13:42:33.000000000 +0200
+++ libc/sysdeps/i386/Makefile	2004-10-22 22:23:53.184368037 +0200
@@ -21,6 +21,10 @@ CFLAGS-dl-load.c += -Wno-unused
 CFLAGS-dl-reloc.c += -Wno-unused
 endif
 
+ifeq ($(subdir),debug)
+CFLAGS-backtrace.c += -fexceptions
+endif
+
 # Most of the glibc routines don't ever call user defined callbacks
 # nor use any FPU or SSE* and as such don't need bigger %esp alignment
 # than 4 bytes.
--- libc/sysdeps/i386/backtrace.c.jj	2003-10-24 14:02:44.000000000 +0200
+++ libc/sysdeps/i386/backtrace.c	2004-10-22 22:23:00.248767985 +0200
@@ -1,5 +1,5 @@
 /* Return backtrace of current program state.
-   Copyright (C) 1998, 2000 Free Software Foundation, Inc.
+   Copyright (C) 1998, 2000, 2003, 2004 Free Software Foundation, Inc.
    This file is part of the GNU C Library.
    Contributed by Ulrich Drepper <drepper@cygnus.com>, 1998.
 
@@ -18,8 +18,64 @@
    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
    02111-1307 USA.  */
 
+#include <bits/libc-lock.h>
+#include <dlfcn.h>
 #include <execinfo.h>
-#include <bp-checks.h>
+#include <stdlib.h>
+#include <unwind.h>
+
+struct trace_arg
+{
+  void **array;
+  int cnt, size;
+  void *lastebp, *lastesp;
+};
+
+#ifdef SHARED
+static _Unwind_Reason_Code (*unwind_backtrace) (_Unwind_Trace_Fn, void *);
+static _Unwind_Ptr (*unwind_getip) (struct _Unwind_Context *);
+static _Unwind_Ptr (*unwind_getcfa) (struct _Unwind_Context *);
+static _Unwind_Ptr (*unwind_getgr) (struct _Unwind_Context *, int);
+
+static void
+init (void)
+{
+  void *handle = __libc_dlopen ("libgcc_s.so.1");
+
+  if (handle == NULL)
+    return;
+
+  unwind_backtrace = __libc_dlsym (handle, "_Unwind_Backtrace");
+  unwind_getip = __libc_dlsym (handle, "_Unwind_GetIP");
+  unwind_getcfa = __libc_dlsym (handle, "_Unwind_GetCFA");
+  unwind_getgr = __libc_dlsym (handle, "_Unwind_GetGR");
+  if (unwind_getip == NULL || unwind_getgr == NULL || unwind_getcfa == NULL)
+    unwind_backtrace = NULL;
+}
+#else
+# define unwind_backtrace _Unwind_Backtrace
+# define unwind_getip _Unwind_GetIP
+# define unwind_getcfa _Unwind_GetCFA
+# define unwind_getgr _Unwind_GetGR
+#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);
+  if (++arg->cnt == arg->size)
+    return _URC_END_OF_STACK;
+
+  /* %ebp is DWARF2 register 5 on IA-32.  */
+  arg->lastebp = (void *) unwind_getgr (ctx, 5);
+  arg->lastesp = (void *) unwind_getcfa (ctx);
+  return _URC_NO_REASON;
+}
 
 
 /* This is a global variable set at program start time.  It marks the
@@ -27,46 +83,61 @@
 extern void *__libc_stack_end;
 
 
-/* This is the stack alyout we see with every stack frame.
+/* This is the stack layout we see with every stack frame
+   if not compiled without frame pointer.
 
             +-----------------+        +-----------------+
     %ebp -> | %ebp last frame--------> | %ebp last frame--->...
             |                 |        |                 |
             | return address  |        | return address  |
             +-----------------+        +-----------------+
-*/
+
+   First try as far to get as far as possible using
+   _Unwind_Backtrace which handles -fomit-frame-pointer
+   as well, but requires .eh_frame info.  Then fall back to
+   walking the stack manually.  */
+
 struct layout
 {
-  struct layout *__unbounded next;
-  void *__unbounded return_address;
+  struct layout *ebp;
+  void *ret;
 };
 
+
 int
 __backtrace (array, size)
      void **array;
      int size;
 {
-  /* We assume that all the code is generated with frame pointers set.  */
-  register void *ebp __asm__ ("ebp");
-  register void *esp __asm__ ("esp");
-  struct layout *current;
-  int cnt = 0;
-
-  /* We skip the call to this function, it makes no sense to record it.  */
-  current = BOUNDED_1 ((struct layout *) ebp);
-  while (cnt < size)
+  struct trace_arg arg = { .array = array, .size = size, .cnt = -1 };
+#ifdef SHARED
+  __libc_once_define (static, once);
+
+  __libc_once (once, init);
+  if (unwind_backtrace == NULL)
+    return 0;
+#endif
+
+  if (size >= 1)
+    unwind_backtrace (backtrace_helper, &arg);
+
+  if (arg.cnt > 1 && arg.array[arg.cnt - 1] == NULL)
+    --arg.cnt;
+  else if (arg.cnt < size)
     {
-      if ((void *) current < esp || (void *) current > __libc_stack_end)
-	/* This means the address is out of range.  Note that for the
-	   toplevel we see a frame pointer with value NULL which clearly is
-	   out of range.  */
-	break;
+      struct layout *ebp = (struct layout *) arg.lastebp;
 
-      array[cnt++] = current->return_address;
-
-      current = current->next;
+      while (arg.cnt < size)
+	{
+	  /* Check for out of range.  */
+	  if ((void *) ebp < arg.lastesp || (void *) ebp > __libc_stack_end
+	      || ((long) ebp & 3))
+	    break;
+
+	  array[arg.cnt++] = ebp->ret;
+	  ebp = ebp->ebp;
+	}
     }
-
-  return cnt;
+  return arg.cnt != -1 ? arg.cnt : 0;
 }
 weak_alias (__backtrace, backtrace)

	Jakub