Re: should minimal symbols be able to force lookup_symbol to return NULL?

[David Carlton <carlton at math dot stanford dot edu>]

On 04 Nov 2002 15:53:43 -0500, Jim Blandy <jimb@redhat.com> said:
> David Carlton <carlton@math.stanford.edu> writes:
>> On 28 Oct 2002 11:16:31 -0800, David Carlton <carlton@math.Stanford.EDU> said:

>>> Currently, it seems to me that, when lookup_symbol_aux is
>>> searching the minsyms, if it finds a minsym without a
>>> corresponding symbol, then lookup_symbol_aux will return NULL
>>> without proceeding on to the check of the static symtabs/psymtabs.

>> This isn't true: it only sometimes does that (if either it can find
>> a symtab at the right address or if it wants to try a name lookup
>> with the mangled name).  Sigh.  This is a mess.

> Yeah.  I don't think that's deliberate behavior, since it doesn't
> happen under any consistent circumstances.

Oh, good.

> I suspect that HP found the same problem you have: look at Rich
> Title's comment below (starting with "RT:"):

> #ifdef HPUXHPPA

>   /* Check for the possibility of the symbol being a function or
>      a global variable that is stored in one of the minimal symbol tables.
>      The "minimal symbol table" is built from linker-supplied info.

>      RT: I moved this check to last, after the complete search of
>      the global (p)symtab's and static (p)symtab's. For HP-generated
>      symbol tables, this check was causing a premature exit from
>      lookup_symbol with NULL return, and thus messing up symbol lookups
>      of things like "c::f". It seems to me a check of the minimal
>      symbol table ought to be a last resort in any case. I'm vaguely
>      worried about the comment below which talks about FORTRAN routines "foo_"
>      though... is it saying we need to do the "minsym" check before
>      the static check in this case? 
>    */

Right.  Though, like Rich, I'm also vaguely worried about the Fortran
comment that comes later.

> Perhaps we should remove the HPUXHPPA conditional, and just do it
> the HPUXHPPA way all the time.

I've got some plausible scenarios which might allow both the HPUXHPPA
and non-HPUXHPPA cases to work without #ifdefs and which would allow
minsyms to be used as a speed optimization without affecting
correctness.  Basically, what they boil down to is keeping the minsym
check in its non-HPUXHPPA location, but making sure that it never
returns a NULL result; since that's what the above comment is
complaining about, it seems plausible that that would allow us to
remove the HPUXHPPA #ifdef.

I'll wait until my first stab at refactoring (which, I hope, preserves
the current behavior exactly) (well, almost exactly: there's one or
two changes which I think of as bugfixes, but it's quite careful about
control flow) gets approved before I submit an RFA for that.
Certainly I'm glad that Joel has appeared and is willing to run
proposed changes through the testsuite on HP/UX machines.

David Carlton
carlton@math.stanford.edu