[PATCH] sandbox: Support signal handling only when requested

[Simon Glass]

Hi Heinrich,

On Mon, 22 Mar 2021 at 18:56, Simon Glass <sjg at chromium.org> wrote:
>
> Hi Heinrich,
>
> On Mon, 22 Mar 2021 at 23:02, Heinrich Schuchardt <xypron.glpk at gmx.de> wrote:
> >
> > On 22.03.21 06:21, Simon Glass wrote:
> > > At present if sandbox crashes it prints a message and tries to exit. But
> > > with the recently introduced signal handler, it often seems to get stuck
> > > in a loop until the stack overflows:
> > >
> > > Segmentation violation
> > >
> > > Segmentation violation
> > >
> > > Segmentation violation
> > >
> > > Segmentation violation
> > >
> > > Segmentation violation
> > >
> > > Segmentation violation
> > >
> > > Segmentation violation
> > > ...
> >
> > Hello Simon,
> >
> > do you have a reproducible example? I never have seen this.
>
> https://source.denx.de/u-boot/custodians/u-boot-dm/-/jobs/242433
>
> You need to run that commit with pytest though...it does not happen
> when run directly.
>
> BTW this sems to expose some rather nasty bug in dlmalloc or how it is
> used. I notice that as soon as the first test is run, the 'top' value
> in dlmalloc is outside the range of the malloc pool, which seems
> wrong. I wonder if there is something broken with how
> dm_test_pre_run() and dm_test_post_run() work.
>
> >
> > Corrupting gd could cause an endless recursive loop, as these lines
> > follow printing the observed string:
> >
> >         printf("pc = 0x%lx, ", pc);
> >         printf("pc_reloc = 0x%lx\n\n", pc - gd->reloc_off);
>
> Yes I suspect printf() is dead.
>
> >
> > If we remove SA_NODEFER from the signal mask in arch/sandbox/cpu/os.c,
> > recursion cannot occur anymore. If a segmentation violation occurs
> > inside the handler it will be delegated to the default handler.
> >
> > Furthermore we could consider removing the signal handler at the start
> > of os_signal_action().
>
> The issue is that if you get a segfault you really don't know if you
> can continue and do anything else.
>
> What is the goal with the signal handler? I don't think the user can
> do anything about it.

I keep hitting this problem during development with sandbox, so I
think I need to apply this patch.

Does anything need to be updated in the tests?

Regards,
Simon