Re: Fwd: Buildbot failure in Wildebeest Builder on whole buildset

[Mark Wielaard <mark@klomp.org>]

Hi Tom,

On Thu, 2021-03-25 at 11:41 +0100, Mark Wielaard wrote:
> On Thu, 2021-03-25 at 09:50 +0100, Tom de Vries wrote:
> > I've just committed patch "Move hardlink handling out of dwz
> > function"
> > and there's this buildbot failure.
> > 
> > Is there something easy that you can do to find out if this is a
> > fluke
> > or not, f.i. retry the build for that bot?
> 
> I logged into the buildbot worker and did a dwz build myself.
> make check does produce 32 unexpected failures.
> Removing the last commit makes everything pass.
> Adding the commit again produces the failures again.
> It isn't a fluke.
> 
> The problem is simply that:
> cp hello 1
> dwz 1
> 
> Makes dwz produce an exit code of 1 which seems to be interpreted as
> child process exited abnormally in a make check run.
> 
> running under valgrind --track-origins=yes gives:
> 
> ==31313== Conditional jump or move depends on uninitialised value(s)
> ==31313==    at 0x127974: dwz (dwz.c:15287)
> ==31313==    by 0x10BB7C: dwz_with_low_mem (dwz.c:16227)
> ==31313==    by 0x10BB7C: dwz_one_file (dwz.c:16253)
> ==31313==    by 0x10BB7C: main (dwz.c:16532)
> ==31313==  Uninitialised value was created by a stack allocation
> ==31313==    at 0x10B59B: main (dwz.c:16513)
> 
> I haven't tracked down what res->res precisely depends on that
> doesn't
> have a defined value.

Note that dwz_one_file was inlined into main, causing valgrind to
pinpoint the wrong frame. Without inlining we get:

==2502== Conditional jump or move depends on uninitialised value(s)
==2502==    at 0x13CF4F: dwz (dwz.c:15287)
==2502==    by 0x13FE3A: dwz_with_low_mem (dwz.c:16227)
==2502==    by 0x13FEAE: dwz_one_file (dwz.c:16253)
==2502==    by 0x140B59: main (dwz.c:16532)
==2502==  Uninitialised value was created by a stack allocation
==2502==    at 0x13FE7F: dwz_one_file (dwz.c:16245)

And indeed we see:

static int
dwz_one_file (const char *file, const char *outfile)
{
  struct file_result res;

  if (stats_p)
    init_stats (file);

  res.die_count = 0;

  return dwz_with_low_mem (file, outfile, &res, NULL);
}

Defines and passes down res, but only initializes the die_count field.

Then in dwz_with_low_mem we simply pass that res to dwz:

  ret = (low_mem_die_limit == 0
         ? 2
         : dwz (file, outfile, res));

And in dwz the first thing we do is:

  if (res->res == -1)
    return 1;

But res->res was never given a value and so could be anything.

Cheers,

Mark