Re: [PATCH] proposed fix for bug # 61144

[Alexander Monakov <amonakov@ispras.ru>]

On Fri, 6 Jun 2014, Rich Felker wrote:

> On Fri, May 23, 2014 at 12:26:18PM -0600, Jeff Law wrote:
> > On 05/21/14 21:59, Rich Felker wrote:
> > >On Wed, May 21, 2014 at 11:17:53AM +0200, Richard Biener wrote:
> > >>On Wed, May 21, 2014 at 3:59 AM, Rich Felker <dalias@libc.org> wrote:
> > >>>Bug # 61144 is a regression in 4.9.0 that breaks building of musl libc
> > >>>due to aggressive and semantically-incorrect constant folding of weak
> > >>>aliases. The attached patch seems to fix the issue. A weak alias
> > >>>should never be a candidate for constant folding because it may always
> > >>>be replaced by a strong definition from another translation unit.
> > >>>
> > >>>For details see https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61144
> > >>>
> > >>>I do not have a copyright assignment on file but this patch should be
> > >>>sufficiently trivial not to require it.
> > >>
> > >>Please add a testcase.  Also I wonder why it isn't better to generalize
> > >
> > >How should a testcase be done? On the PR there's a testcase that shows
> > >the problem in the generated code, but no automated check for it.
> > >Testing this is actually a bit of a pain unless you're allowed to run
> > >the generated program.
> > You can run the test program.  Have it exit (0) on success, abort ()
> > on failure if at all possible.  Then drop the test source file into
> > gcc/testsuite/gcc.c-torture/execute/pr61144.c
> 
> The test needs to be two translation units linked together: one with
> a weak definition of the object as 0, and the other with a strong
> definition. The test should show the weak value being used rather than
> the strong one. But I'm not sure how this should be integrated with
> the build process.

Please have a look at gcc/testsuite/gcc.dg/special/wkali-2{,a,b}.c.  This is a
three-TU test for weak aliases, so you should be able to very easily adjust it
for this bug.

Thanks.
Alexander