Re: Macro code crasher on re-run

[Jim Blandy <jimb at redhat dot com>]

Daniel Jacobowitz <drow@mvista.com> writes:
> There's a bug in default_macro_scope.

Only one?!?  :)

> 97
> 98        /* If all else fails, fall back to the current listing position.  */
> 99        else
> 100         {
> 101           /* Don't call select_source_symtab here.  That can raise an
> 102              error if symbols aren't loaded, but GDB calls the expression
> 103              evaluator in all sorts of contexts.
> 104
> 105              For example, commands like `set width' call the expression
> 106              evaluator to evaluate their numeric arguments.  If the
> 107              current language is C, then that may call this function to
> 108              choose a scope for macro expansion.  If you don't have any
> 109              symbol files loaded, then get_current_or_default would raise an
> 110              error.  But `set width' shouldn't raise an error just because
> 111              it can't decide which scope to macro-expand its argument in.  */
> 112           struct symtab_and_line cursal = 
> 113                             get_current_source_symtab_and_line ();
> 114           
> 115           sal.symtab = cursal.symtab;
> 116           sal.line = cursal.line;
> 117         }
> 
> So we initialize just the symtab and line pointers.
> 118
> 119       return sal_macro_scope (sal);
> 120     }
> 
> 
> 39        if (! sal.symtab
> 40            || ! sal.symtab->macro_table)
> 41          return 0;
> 
> Oops, uninitialized memory read.  That else case can't work; Jim, should we
> just return 0 from default_macro_scope if the target isn't running, or
> is there a function I don't see somewhere to find the macrotab and
> initialize the rest of the symtab?  Should it be "sal = cursal"?

I don't follow.  All default_macro_scope's callers check for null
return; it's documented to return zero at times.  So you must be
talking about that code in sal_macro_scope itself.  Line 39 refers to
sal.symtab, initialized by line 115, so you must be talking about line
40.  But sal.symtab must be non-zero, or else we wouldn't reach the
right operand of the ||.

Or should I sleep and try again?