Re: [PATCH][PR symtab/17855] Fix.

[Doug Evans <xdje42 at gmail dot com>]

Pedro Alves <palves@redhat.com> writes:
> On 01/20/2015 06:26 AM, Doug Evans wrote:
>> Hi.
>> 
>> This patch fixes symtab/17855.
>> Basically the issue is that breakpoint_re_set is currently being called
>> before observer_notify_new_objfile (NULL), and thus the ada symbol
>> cache (and the general symbol cache of a separate patch) aren't being
>> flushed first, so that when breakpoints are reset symbol lookup is being
>> done on a stale cache.
>> 
>> Regression tested on amd64-linux.
>> 
>> 2015-01-19  Doug Evans  <xdje42@gmail.com>
>> 
>> 	PR symtab/17855
>> 	* symfile.c (clear_symtab_users): Notify observers of change before
>> 	calling breakpoint_re_set.
>> 
>> diff --git a/gdb/symfile.c b/gdb/symfile.c
>> index d55e361..ad481de 100644
>> --- a/gdb/symfile.c
>> +++ b/gdb/symfile.c
>> @@ -3023,6 +3023,12 @@ clear_symtab_users (int add_flags)
>>    /* Someday, we should do better than this, by only blowing away
>>       the things that really need to be blown.  */
>>  
>> +  /* Notify anyone listening that the previous loaded symtab(s) are invalid.
>> +     It is important to do this before calling breakpoint_re_set as the latter
>> +     will try to look up symbols, and for example the symbol cache needs to
>> +     be flushed first.  */
>> +  observer_notify_new_objfile (NULL);
>> +
>>    /* Clear the "current" symtab first, because it is no longer valid.
>>       breakpoint_re_set may try to access the current symtab.  */
>>    clear_current_source_symtab_and_line ();
>> @@ -3032,7 +3038,6 @@ clear_symtab_users (int add_flags)
>>      breakpoint_re_set ();
>>    clear_last_displayed_sal ();
>>    clear_pc_function_cache ();
>> -  observer_notify_new_objfile (NULL);
>
> Looking at the whole function, ISTM that the breakpoint_re_set
> call should move further down.  I can imagine that breakpoint_re_set
> could well hit a stale pc function cache, cleared only after by
> clear_pc_function_cache.  breakpoint.c:parse_breakpoint_sals also
> references the last displayed sal.  One would hope that breakpoint
> re-set is independent of that, though the existing comment about
> breakpoint_re_set accessing the current symtab leaves me
> wondering.  WDYT?
>
> Thanks,
> Pedro Alves

Like so?

2015-01-28  Doug Evans  <xdje42@gmail.com>

	PR symtab/17855
	* symfile.c (clear_symtab_users): Move call to breakpoint_re_set
	closer to end.

diff --git a/gdb/symfile.c b/gdb/symfile.c
index d55e361..bad244c 100644
--- a/gdb/symfile.c
+++ b/gdb/symfile.c
@@ -3023,13 +3023,8 @@ clear_symtab_users (int add_flags)
   /* Someday, we should do better than this, by only blowing away
      the things that really need to be blown.  */
 
-  /* Clear the "current" symtab first, because it is no longer valid.
-     breakpoint_re_set may try to access the current symtab.  */
   clear_current_source_symtab_and_line ();
-
   clear_displays ();
-  if ((add_flags & SYMFILE_DEFER_BP_RESET) == 0)
-    breakpoint_re_set ();
   clear_last_displayed_sal ();
   clear_pc_function_cache ();
   observer_notify_new_objfile (NULL);
@@ -3040,9 +3035,19 @@ clear_symtab_users (int add_flags)
   expression_context_block = NULL;
   innermost_block = NULL;
 
+  /* Now that most everything has been reset, reset any existing breakpoints.
+     Reasons for doing this after the above are that breakpoint resetting may
+     involve:
+     - reading the current source symtab and line,
+     - reading the last displayed sal,
+     - reading the pc function cache,
+     - symbol lookup which requires, for example, invalidating any caches
+       first.  */
+  if ((add_flags & SYMFILE_DEFER_BP_RESET) == 0)
+    breakpoint_re_set ();
+
   /* Varobj may refer to old symbols, perform a cleanup.  */
   varobj_invalidate ();
-
 }
 
 static void