Re: [PATCH][RFC] Sanitize equals and hash functions in hash-tables.

[Richard Biener <richard.guenther@gmail.com>]

On Wed, May 22, 2019 at 11:13 AM Martin Liška <mliska@suse.cz> wrote:
>
> On 5/21/19 1:51 PM, Richard Biener wrote:
> > On Tue, May 21, 2019 at 1:02 PM Martin Liška <mliska@suse.cz> wrote:
> >>
> >> On 5/21/19 11:38 AM, Richard Biener wrote:
> >>> On Tue, May 21, 2019 at 12:07 AM Jeff Law <law@redhat.com> wrote:
> >>>>
> >>>> On 5/13/19 1:41 AM, Martin Liška wrote:
> >>>>> On 11/8/18 9:56 AM, Martin Liška wrote:
> >>>>>> On 11/7/18 11:23 PM, Jeff Law wrote:
> >>>>>>> On 10/30/18 6:28 AM, Martin Liška wrote:
> >>>>>>>> On 10/30/18 11:03 AM, Jakub Jelinek wrote:
> >>>>>>>>> On Mon, Oct 29, 2018 at 04:14:21PM +0100, Martin Liška wrote:
> >>>>>>>>>> +hashtab_chk_error ()
> >>>>>>>>>> +{
> >>>>>>>>>> +  fprintf (stderr, "hash table checking failed: "
> >>>>>>>>>> +           "equal operator returns true for a pair "
> >>>>>>>>>> +           "of values with a different hash value");
> >>>>>>>>> BTW, either use internal_error here, or at least if using fprintf
> >>>>>>>>> terminate with \n, in your recent mail I saw:
> >>>>>>>>> ...different hash valueduring RTL pass: vartrack
> >>>>>>>>>                     ^^^^^^
> >>>>>>>> Sure, fixed in attached patch.
> >>>>>>>>
> >>>>>>>> Martin
> >>>>>>>>
> >>>>>>>>>> +  gcc_unreachable ();
> >>>>>>>>>> +}
> >>>>>>>>>   Jakub
> >>>>>>>>>
> >>>>>>>> 0001-Sanitize-equals-and-hash-functions-in-hash-tables.patch
> >>>>>>>>
> >>>>>>>> From 0d9c979c845580a98767b83c099053d36eb49bb9 Mon Sep 17 00:00:00 2001
> >>>>>>>> From: marxin <mliska@suse.cz>
> >>>>>>>> Date: Mon, 29 Oct 2018 09:38:21 +0100
> >>>>>>>> Subject: [PATCH] Sanitize equals and hash functions in hash-tables.
> >>>>>>>>
> >>>>>>>> ---
> >>>>>>>>  gcc/hash-table.h | 40 +++++++++++++++++++++++++++++++++++++++-
> >>>>>>>>  1 file changed, 39 insertions(+), 1 deletion(-)
> >>>>>>>>
> >>>>>>>> diff --git a/gcc/hash-table.h b/gcc/hash-table.h
> >>>>>>>> index bd83345c7b8..694eedfc4be 100644
> >>>>>>>> --- a/gcc/hash-table.h
> >>>>>>>> +++ b/gcc/hash-table.h
> >>>>>>>> @@ -503,6 +503,7 @@ private:
> >>>>>>>>
> >>>>>>>>    value_type *alloc_entries (size_t n CXX_MEM_STAT_INFO) const;
> >>>>>>>>    value_type *find_empty_slot_for_expand (hashval_t);
> >>>>>>>> +  void verify (const compare_type &comparable, hashval_t hash);
> >>>>>>>>    bool too_empty_p (unsigned int);
> >>>>>>>>    void expand ();
> >>>>>>>>    static bool is_deleted (value_type &v)
> >>>>>>>> @@ -882,8 +883,12 @@ hash_table<Descriptor, Allocator>
> >>>>>>>>    if (insert == INSERT && m_size * 3 <= m_n_elements * 4)
> >>>>>>>>      expand ();
> >>>>>>>>
> >>>>>>>> -  m_searches++;
> >>>>>>>> +#if ENABLE_EXTRA_CHECKING
> >>>>>>>> +    if (insert == INSERT)
> >>>>>>>> +      verify (comparable, hash);
> >>>>>>>> +#endif
> >>>>>>>>
> >>>>>>>> +  m_searches++;
> >>>>>>>>    value_type *first_deleted_slot = NULL;
> >>>>>>>>    hashval_t index = hash_table_mod1 (hash, m_size_prime_index);
> >>>>>>>>    hashval_t hash2 = hash_table_mod2 (hash, m_size_prime_index);
> >>>>>>>> @@ -930,6 +935,39 @@ hash_table<Descriptor, Allocator>
> >>>>>>>>    return &m_entries[index];
> >>>>>>>>  }
> >>>>>>>>
> >>>>>>>> +#if ENABLE_EXTRA_CHECKING
> >>>>>>>> +
> >>>>>>>> +/* Report a hash table checking error.  */
> >>>>>>>> +
> >>>>>>>> +ATTRIBUTE_NORETURN ATTRIBUTE_COLD
> >>>>>>>> +static void
> >>>>>>>> +hashtab_chk_error ()
> >>>>>>>> +{
> >>>>>>>> +  fprintf (stderr, "hash table checking failed: "
> >>>>>>>> +     "equal operator returns true for a pair "
> >>>>>>>> +     "of values with a different hash value\n");
> >>>>>>>> +  gcc_unreachable ();
> >>>>>>>> +}
> >>>>>>> I think an internal_error here is probably still better than a simple
> >>>>>>> fprintf, even if the fprintf is terminated with a \n :-)
> >>>>>> Fully agree with that, but I see a lot of build errors when using internal_error.
> >>>>>>
> >>>>>>> The question then becomes can we bootstrap with this stuff enabled and
> >>>>>>> if not, are we likely to soon?  It'd be a shame to put it into
> >>>>>>> EXTRA_CHECKING, but then not be able to really use EXTRA_CHECKING
> >>>>>>> because we've got too many bugs to fix.
> >>>>>> Unfortunately it's blocked with these 2 PRs:
> >>>>>> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87845
> >>>>>> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87847
> >>>>> Hi.
> >>>>>
> >>>>> I've just added one more PR:
> >>>>> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90450
> >>>>>
> >>>>> I'm sending updated version of the patch that provides a disablement for the 3 PRs
> >>>>> with a new function disable_sanitize_eq_and_hash.
> >>>>>
> >>>>> With that I can bootstrap and finish tests. However, I've done that with a patch
> >>>>> limits maximal number of checks:
> >>>> So rather than call the disable_sanitize_eq_and_hash, can you have its
> >>>> state set up when you instantiate the object?  It's not a huge deal,
> >>>> just thinking about loud.
> >>>>
> >>>>
> >>>>
> >>>> So how do we want to go forward, particularly the EXTRA_EXTRA checking
> >>>> issue :-)
> >>>
> >>> There is at least one PR where we have a table where elements _in_ the
> >>> table are never compared against each other but always against another
> >>> object (I guess that's usual even), but the setup is in a way that the
> >>> comparison function only works with those.  With the patch we verify
> >>> hashing/comparison for something that is never used.
> >>>
> >>> So - wouldn't it be more "correct" to only verify comparison/hashing
> >>> at lookup time, using the object from the lookup and verify that against
> >>> all other elements?
> >>
> >> I don't a have problem with that. Apparently this changes fixes
> >> PR90450 and PR87847.
> >>
> >> Changes from previous version:
> >> - verification happens only when an element is searched (not inserted)
> >> - new argument 'sanitize_eq_and_hash' added for hash_table::hash_table
> >> - new param has been introduced hash-table-verification-limit in order
> >>   to limit number of elements that are compared within a table
> >> - verification happens only with flag_checking >= 2
> >>
> >> I've been bootstrapping and testing the patch right now.
> >
> > Looks like I misremembered the original patch.  The issue isn't
> > comparing random two elements in the table.
> >
> > That it fixes PR90450 is because LIM never calls find_slot_with_hash
> > without INSERTing.
> >
>
> There's updated version of the patch where I check all find operations
> (both w/ and w/o insertion).
>
> Patch can bootstrap on x86_64-linux-gnu and survives regression tests
> except for:
>
> $ ./xgcc -B. /home/marxin/Programming/gcc/gcc/testsuite/gcc.dg/torture/pr63941.c -O2 -c
> hash table checking failed: equal operator returns true for a pair of values with a different hash value
> during GIMPLE pass: lim
> /home/marxin/Programming/gcc/gcc/testsuite/gcc.dg/torture/pr63941.c: In function ‘fn1’:
> /home/marxin/Programming/gcc/gcc/testsuite/gcc.dg/torture/pr63941.c:6:1: internal compiler error: in hashtab_chk_error, at hash-table.h:1019
>     6 | fn1 ()
>       | ^~~
> 0x6c5725 hashtab_chk_error
>         /home/marxin/Programming/gcc/gcc/hash-table.h:1019
> 0xe504ea hash_table<mem_ref_hasher, false, xcallocator>::verify(ao_ref* const&, unsigned int)
>         /home/marxin/Programming/gcc/gcc/hash-table.h:1040
> 0xe504ea hash_table<mem_ref_hasher, false, xcallocator>::find_slot_with_hash(ao_ref* const&, unsigned int, insert_option)
>         /home/marxin/Programming/gcc/gcc/hash-table.h:960
> 0xe504ea gather_mem_refs_stmt
>         /home/marxin/Programming/gcc/gcc/tree-ssa-loop-im.c:1501
> 0xe504ea analyze_memory_references
>         /home/marxin/Programming/gcc/gcc/tree-ssa-loop-im.c:1625
> 0xe504ea tree_ssa_lim
>         /home/marxin/Programming/gcc/gcc/tree-ssa-loop-im.c:2646
> 0xe504ea execute
>         /home/marxin/Programming/gcc/gcc/tree-ssa-loop-im.c:2708
>
> Richi: it's after your recent patch.

I can't reproduce this (but I have a slightly patched tree).

Richard.

> For some reason I don't see PR87847 issue any longer.
>
>
> May I install the patch with disabled sanitization in tree-ssa-loop-im.c ?
>
> Thanks,
> Martin
>
> > I guess PR90450 is "real" indeed...
> >
> > Richard.
> >
> >> Martin
> >>
> >>>
> >>> Richard.
> >>>
> >>>>
> >>>> Jeff
> >>
>