Re: [PATCH v3 06/11] kselftest: arm64: fake_sigreturn_bad_magic

[Dave Martin <Dave.Martin@arm.com>]

On Wed, Sep 04, 2019 at 11:37:36AM +0100, Cristian Marussi wrote:
> On 04/09/2019 11:05, Dave Martin wrote:
> > On Fri, Aug 30, 2019 at 03:29:29PM +0100, Cristian Marussi wrote:
> >> Hi
> >>
> >> On 13/08/2019 17:25, Dave Martin wrote:
> >>> On Fri, Aug 02, 2019 at 06:02:55PM +0100, Cristian Marussi wrote:
> > 
> > [...]
> > 
> >>>> diff --git a/tools/testing/selftests/arm64/signal/testcases/fake_sigreturn_bad_magic.c b/tools/testing/selftests/arm64/signal/testcases/fake_sigreturn_bad_magic.c
> > 
> > [...]
> > 
> >>>> +static int fake_sigreturn_bad_magic_run(struct tdescr *td,
> >>>> +					siginfo_t *si, ucontext_t *uc)
> >>>> +{
> >>>> +	size_t resv_sz, offset;
> >>>> +	struct _aarch64_ctx *shead = GET_SF_RESV_HEAD(sf), *head;
> >>>> +
> >>>> +	/* just to fill the ucontext_t with something real */
> >>>> +	if (!get_current_context(td, &sf.uc))
> >>>> +		return 1;
> >>>> +
> >>>> +	resv_sz = GET_SF_RESV_SIZE(sf);
> >>>> +	/*
> >>>> +	 * find the terminator, preserving existing headers
> >>>> +	 * and verify amount of spare room in __reserved area.
> >>>> +	 */
> >>>> +	head = get_terminator(shead, resv_sz, &offset);
> >>>> +	/*
> >>>> +	 * try stripping extra_context header when low on space:
> >>>> +	 * we need at least 2*HDR_SZ space ... one for the KSFT_BAD_MAGIC
> >>>> +	 * and the other for the usual terminator.
> >>>> +	 */
> >>>> +	if (head && resv_sz - offset < HDR_SZ * 2) {
> >>>
> >>> Can we factor out this logic for finding space in the signal frame?
> >>>
> >>> We do pretty much the same thing in all the fake_sigreturn tests...
> >>
> >> Ok
> >>>
> >>>> +		fprintf(stderr, "Low on space:%zd. Discarding extra_context.\n",
> >>>> +			resv_sz - offset);
> >>>> +		head = get_header(shead, EXTRA_MAGIC, resv_sz, &offset);
> >>>> +	}
> >>>> +	/* just give up and timeout if still not enough space */
> >>>
> >>> Do we actually time out?  I don't see where we actually wait, so doesn't
> >>> test_run() just fail immediately?
> >>>
> >>> The same applies to all the other fake_sigreturn tests too.
> >>>
> >> Right. It is probably a leftover.
> >>
> >> SIGALRM is used as an extreme measure to kill tests gone bad, but this
> >> can happen only once the fake sigframe has been effectively placed on the stack
> >> and sigreturned.
> > 
> > OK, so this gets reported as a test failure because with no SIGSEGV,
> > nothing ever sets td->pass?
> 
> Yes exactly. End result is based on value on td->pass, in case of abrupt
> termination or timeout nobody sets td->pass ever.
> > 
> > This is probably OK for now, though I wonder whether this should be
> > reported as a skipped test instead.
> > 
> > In case of doubt, reporting a failure is preferable anyway, since that
> > will encourage people actually to investigate what went wrong.
> > 
> 
> As of now I never skip a test in fact...also tests for unsupported features
> are built and run expecting a SIGILL, and reported as PASS in that case.

OK, just wanted to check I'd understood correcly.

Cheers
---Dave