Re: gdb_assert when resetting breakpoints

[Kai Tietz <ktietz70@googlemail.com>]

Hello all,

any reply would be kind

Cheers,
Kai

2009/3/17 Kai Tietz <Kai.Tietz@onevision.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
>
> |  (\_/)  This is Bunny. Copy and paste Bunny
> | (='.'=) into your signature to help him gain
> | (")_(") world domination.
>
> 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);
>



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