Re: gdb_assert when resetting breakpoints

[Kai Tietz <Kai dot Tietz at onevision dot com>]

gdb-owner@sourceware.org wrote on 10.03.2009 15:02:40:

> Hi...
> 
> When using current gdb cvs head sources I encounter a gdb_assert() in 
> breakpoint.c line 7451.
> This is in function breakpoint_re_set_one().
> Let me tell you what I am doing to get it (reproduceably). I am not a 
> guru to gdb's internals so
> please forgive me if I conclude something wrong.
> 
> I am having a mixed C and Objective C application. I am running on 
> windows using GNUstep
> for my ObjC Foundation classes. GNUstep-base is a shared library loaded 
> lazy.
> Due to the nature of this bug I assume that this will also appear on 
> other platforms like linux
> (according to my analysis). So it is not windows specific.
> 
> I start gdb and set a breakpoint to main() using "b main". Then I run my 

> app using "r".
> A few seconds later I get the assert in breakpoint.c:7451 
> gdb_assert(sals.nelts==1).
> When I debug into it sals.nelts == 2. The assert happens when the 
> gnustep-base shared
> library was loaded.
> 
> What has happenend: In breakpoint.c line 7417 you find:
> sals = decode_line_1 (&s, 1, (struct symtab *) NULL, 0, (char ***) 
> NULL,not_found_ptr);
> s points to "main" at that moment as found in the breakpoint structure 
> supplied to breakpoint_re_set_one().
> 
> sals (returned from decode_line_1) contains 2 entries.
> Sals entry 0 points to the ObjectiveC METHOD main of the foundation base 

> class NSThread
> (written in ObjC notation -[NSThread main]). This is a real ObjC 
> baseclass not something
> from my own code. It has also nothing to do with an application's 
> entrypoint. It also perfectly
> legal in ObjectiveC to name methods like C functions. They do not 
collide.
> Sals entry 1 points to the function "main()" of my application. This is 
> the entry which I think is
> the correct one to use here.
> 
> Obviously decode_line_1 returns every symbol matching a certain string 
> independant of
> its language. As far as I understand gdb at the moment this appears to 
> be ok.
> 
> So what is the correct behaviour here to fix this problem? I assume that 

> there might be more
> areas of symbol duplicates that can occur not only main() vs -[NSThread 
> main].
> 
> Maybe the assert should be replaced by a loop over the sals entries 
> matching the infos from the
> breakpoint structure passed to breakpoint_re_set_one() and the 
> individual symtab entry of one
> sals entry by filename(?) matching?
> 
> Thanks in advance for your help,
> 
> Roland
> 
> 

Hi,

I prepared a patch for this issue, which should solve the described 
problem of Roland.

Changelog:

2009-03-17  Kai Tietz  <Kai.Tietz@onevision.com>

        * breakpoint.c: take care about multiple breakpoints
        possibilities when resetting breakpoints.


Is this patch ok for apply?

Cheers,
Kai

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Patch:

Index: src/gdb/breakpoint.c
===================================================================
--- src.orig/gdb/breakpoint.c   2009-03-17 11:10:45.000000000 +0100
+++ src/gdb/breakpoint.c        2009-03-17 11:19:01.890880000 +0100
@@ -57,6 +57,7 @@
 #include "top.h"
 #include "wrapper.h"
 #include "valprint.h"
+#include "filenames.h"
 
 #include "mi/mi-common.h"
 
@@ -7392,6 +7393,7 @@
   struct breakpoint *b = (struct breakpoint *) bint;
   struct value *mark;
   int i;
+  int sals_index = -1;
   int not_found = 0;
   int *not_found_ptr = &not_found;
   struct symtabs_and_lines sals = {};
@@ -7455,20 +7457,59 @@
       if (not_found)
        break;
 
-      gdb_assert (sals.nelts == 1);
-      resolve_sal_pc (&sals.sals[0]);
-      if (b->condition_not_parsed && s && s[0])
+      /* If only one sals entry is found use it directly
+        elsewise cycle over all sals and match breakpoint
+        against all returned sals by checking filenames and
+        linenumbers. */
+      if (sals.nelts == 1)
+       sals_index = 0;
+      else
+       {
+         for (i=0;(i < sals.nelts) && (sals_index == -1);i++)
+           {
+             int symtab_linenum = sals.sals[i].line;
+             int bpoint_linenum = b->line_number;
+
+             if (symtab_linenum == bpoint_linenum)
+               {
+                 struct symtab *s = sals.sals[i].symtab;
+
+                 if (s)
+                   {
+                     const char *symtab_filename = s->filename;
+                     const char *bpoint_filename = b->source_file;
+
+                     if (symtab_filename)
+                       symtab_filename = lbasename(symtab_filename);
+
+                     if (bpoint_filename)
+                       bpoint_filename = lbasename(bpoint_filename);
+
+                     if (bpoint_filename && symtab_filename
+                         && 
(FILENAME_CMP(bpoint_filename,symtab_filename)
+                             == 0))
+                       sals_index = i;
+                   }
+               }
+           }
+       }
+      gdb_assert(sals_index != -1);
+      if (sals_index == -1)
+       break;
+
+      resolve_sal_pc (&sals.sals[sals_index]);
+      if (b->condition_not_parsed && s && s[sals_index])
        {
          char *cond_string = 0;
          int thread = -1;
-         find_condition_and_thread (s, sals.sals[0].pc, 
+         find_condition_and_thread (s, sals.sals[sals_index].pc, 
                                     &cond_string, &thread);
          if (cond_string)
            b->cond_string = cond_string;
          b->thread = thread;
          b->condition_not_parsed = 0;
        }
-      expanded = expand_line_sal_maybe (sals.sals[0]);
+      expanded = expand_line_sal_maybe (sals.sals[sals_index]);
       cleanups = make_cleanup (xfree, sals.sals);
       update_breakpoint_locations (b, expanded);
       do_cleanups (cleanups);