Re: [RFC PATCH] test-c-stack2.sh: skip if the platform sent SIGILL on an invalid address.

[Dmitry V. Levin]

On Sat, Dec 29, 2018 at 02:31:11PM +0300, Andrey Savchenko wrote:
> On Sat, 29 Dec 2018 12:17:32 +0100 Bruno Haible wrote:
> > > As for the SIGILL peculiarity, it has a reason in the Elbrus 
> > > architecture. 
> > > ...
> > > And it's not a segmentation fault.
> > 
> > I believe you should make it signal a SIGSEGV or SIGBUS, not SIGILL, for
> > the following reasons:
> > 
> > * Look at the second table in
> >   http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/signal.h.html.
> >   It defines a couple of signal codes for SIGILL, SIGSEGV, and SIGBUS.
> >   It implies that SIGILL means an invalid instruction (and "illegal operand"
> >   means an invalid operand that is in the instruction stream).
> >   Whereas SIGSEGV and SIGBUS mean a problem with an instruction in 
> > combination
> >   with a memory address.
> > 
> > * The main users of SIGSEGV and SIGBUS are catching stack overflow, garbage
> >   collection, and similar (e.g. by use of GNU libsigsegv). The fact that
> >   you observe an incompatibility between your Linux adaptation and
> >   application programs that work fine across Linux/BSD/AIX/Solaris is a sure
> >   indication that you will encounter similar incompatibilities along the 
> > lines,
> >   until you fix that port, to produce SIGSEGV or SIGBUS instead of SIGILL.
> 
> This is not possible. Four generations of hardware are already
> manufactured and they use SIGILL for such cases. It may be fixed in
> future generations if CPU designers will agree to do so, but we
> have to deal with already produced and used in production hardware.

It's all up to the kernel what signal to generate in response
to that particular non-SIGSEGV kind of trap.

I agree with Bruno here, as long as the code in question causes SIGILL,
the architecture is not compatible and its users will suffer more
because of this unneeded incompatibility.


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