Re: [PATCH] varasm: Fix type confusion bug

[Alex Coplan <alex.coplan@arm.com>]

On 01/12/2022 16:12, Richard Sandiford wrote:
> Alex Coplan via Gcc-patches <gcc-patches@gcc.gnu.org> writes:
> > Hi,
> >
> > This patch fixes a type confusion bug in varasm.cc:assemble_variable.
> > The problem is that the current code calls:
> >
> >   sect = get_variable_section (decl, false);
> >
> > and then accesses sect->named.name without checking whether the section
> > is in fact a named section. In the surrounding else clause, we only know
> > that SECTION_STYLE (sect) != SECTION_NOSWITCH, so it is possible that
> > the section is an unnamed section.
> >
> > In practice, this means that we end up doing a wild string compare
> > between a function pointer and the string literal ".vtable_map_vars".
> > This is because sect->named.name aliases sect->unnamed.callback in the
> > section union.
> >
> > This can be seen in GDB with a simple testcase such as "int x;".
> >
> > This patch fixes the issue by checking the SECTION_STYLE of the section
> > is in fact SECTION_NAMED before trying to do the string comparison.
> >
> > We drop the existing check of whether sect->named.name is non-NULL
> > because this should presumably always be the case for a named section.
> >
> > Bootstrapped/regtested on aarch64-none-linux-gnu, OK for trunk?
> 
> OK, thanks.  I think it's OK for backports too if you like,
> since it's a regression from around 2013.

Thanks, I've pushed the patch to trunk, and will backport if there are
no complaints after a week or so.

Alex

> 
> Richard
> 
> >
> > Thanks,
> > Alex
> >
> > gcc/ChangeLog:
> >
> > 	* varasm.cc (assemble_variable): Fix type confusion bug when
> > 	checking for ".vtable_map_vars" section.
> >
> > diff --git a/gcc/varasm.cc b/gcc/varasm.cc
> > index 9dfbebbb915..6851201b6a2 100644
> > --- a/gcc/varasm.cc
> > +++ b/gcc/varasm.cc
> > @@ -2400,7 +2400,7 @@ assemble_variable (tree decl, int top_level ATTRIBUTE_UNUSED,
> >    else
> >      {
> >        /* Special-case handling of vtv comdat sections.  */
> > -      if (sect->named.name
> > +      if (SECTION_STYLE (sect) == SECTION_NAMED
> >  	  && (strcmp (sect->named.name, ".vtable_map_vars") == 0))
> >  	handle_vtv_comdat_section (sect, decl);
> >        else