Re: [PATCH] Export stack_used as __stack_used

[Florian Weimer <fweimer at redhat dot com>]

On 06/17/2016 10:17 PM, Gary Benson wrote:
> Gary Benson wrote:
> > Florian Weimer wrote:
> > > On 06/17/2016 01:37 PM, Gary Benson wrote:
> > > > This commit renames "stack_used" as "__stack_used" and changes it
> > > > from a static variable in allocatestack.c to an internally
> > > > exported symbol available to all nptl source files.  This fixes
> > > > bug 17629 (and thus GDB PR 9635).
> > >
> > > What do you mean by âexportâ?  The __ prefix suggests that you want
> > > to export it as a symbol (probably GLIBC_PRIVATE), but I think you'd
> > > need to update nptl/Versions in this case.
> >
> > No, I don't need that, it needs to be visible outside allocatestack.c
> > but it doesn't need to be visible in, e.g., the output of "objdump -T".
> >
> > > If the variable remains nptl-internal, I expect that you could turn
> > > it into a hidden symbol, and keep its current name.
> >
> > I may be wrong but I think its the rename that fixes the GDB bug.
> >
> > If it's visible outside of allocatestack.c (i.e. it's not "static")
> > then it should be named with a double-underscore, no?
>
> Oh, hang on, libthread_db looks it up _by_name_.  How is that working
> currently?

It seems that libpthread_db calls ps_pglobal_lookup, which is provided 
by the âapplicationâ (so GDB).  The mechanism is a bit weird: it almost 
looks as if someone thought about caching the name-based lookups in an 
array (with an index known at compile-time), but then never wrote the 
code to use a cache.

We check that the symbols can be found in the .symtab section (so via 
debugging information, I assume, not .dynsym).

Florian