Re: [PATCH] Make strlen range computations more conservative

[Maxim Kuvyrkov <maxim dot kuvyrkov at linaro dot org>]

Hi Jeff,
Hi Bernd,

This change (git commit d0eb64b248a9e40dfa633c4e4baebc3b238fd6eb / svn rev. 263793) causes a segfault when build Linux kernel for AArch64.  The exact configuration is 
===
git_repo[linux]=https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
git_branch[linux]=linux-4.14.y
git_repo[gcc]=git://gcc.gnu.org/git/gcc.git
git_branch[gcc]=master
linux_config=allmodconfig
===

The bisection artifacts point at this exact commit:
Parent commit 0584c3707994997f5dc9fa79732d01a53c25db6a can build 18083 objects.
This commit d0eb64b248a9e40dfa633c4e4baebc3b238fd6eb can build 18076 objects from the same linux tree.

The relevant error (see [1]):
==
during GIMPLE pass: dse
drivers/md/dm-mpath.c: In function 'multipath_init_per_bio_data':
drivers/md/dm-mpath.c:2032:1: internal compiler error: Segmentation fault
==

Full bisection artifacts are at [2].

Bernd, would you please investigate?

IMO, this should be easy to reproduce from the bisection logs, but let me know if it's not straightforward.  Best ping on IRC (I'm maximk) or follow up here. 

FYI, there is another regression (either caused or unmasked by Kugan's gcc commit b88c25691cf8b153db44108935db871e1d40db89), but it appears orthogonal to this one.

[1] https://ci.linaro.org/view/tcwg_kernel-gnu/job/tcwg_kernel-bisect-gnu-master-aarch64-lts-allmodconfig/8/artifact/artifacts/build-d0eb64b248a9e40dfa633c4e4baebc3b238fd6eb/5-count_linux_objs/console.log/*view*/

[2] https://ci.linaro.org/view/tcwg_kernel-gnu/job/tcwg_kernel-bisect-gnu-master-aarch64-lts-allmodconfig/8/artifact/artifacts/

Regards,

--
Maxim Kuvyrkov
www.linaro.org



> On Aug 22, 2018, at 2:43 AM, Jeff Law <law@redhat.com> wrote:
> 
> [ I'm still digesting, but saw something in this that ought to be broken
> out... ]
> 
> On 08/19/2018 09:55 AM, Bernd Edlinger wrote:
>> diff -Npur gcc/tree-ssa-dse.c gcc/tree-ssa-dse.c
>> --- gcc/tree-ssa-dse.c	2018-07-18 21:21:34.000000000 +0200
>> +++ gcc/tree-ssa-dse.c	2018-08-19 14:29:32.344498771 +0200
>> @@ -248,6 +248,12 @@ compute_trims (ao_ref *ref, sbitmap live
>> 	 residual handling in mem* and str* functions is usually
>> 	 reasonably efficient.  */
>>       *trim_tail = last_orig - last_live;
>> +      /* Don't fold away an out of bounds access, as this defeats proper
>> +	 warnings.  */
>> +      if (*trim_tail
>> +	  && compare_tree_int (TYPE_SIZE_UNIT (TREE_TYPE (ref->base)),
>> +			       last_orig) <= 0)
>> +	*trim_tail = 0;
>>     }
>>   else
>>     *trim_tail = 0;
> This seems like a good change in and of itself and should be able to go
> forward without further review work.   Consider this hunk approved,
> along with any testsuite you have which tickles this code (I didn't
> immediately see one attached to this patch.  But I could have missed it).
> 
> Jeff