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

From: Dave Martin <[email-masked]>
Date: Wed, 4 Sep 2019 11:05:19 +0100

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?

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.

[...]

Cheers
---Dave

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