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

["Martin Liška" <mliska@suse.cz>]

On 6/10/19 8:21 PM, Jason Merrill wrote:
> On Mon, Jun 10, 2019 at 3:08 AM Martin Liška <mliska@suse.cz> wrote:
>> On 6/7/19 11:43 PM, Jason Merrill wrote:
>>> On Fri, Jun 7, 2019 at 8:14 AM Martin Liška <mliska@suse.cz> wrote:
>>>> On 6/7/19 2:09 PM, Richard Biener wrote:
>>>>> On Fri, Jun 7, 2019 at 2:03 PM Martin Liška <mliska@suse.cz> wrote:
>>>>>> On 6/7/19 10:57 AM, Richard Biener wrote:
>>>>>>> On Mon, Jun 3, 2019 at 3:35 PM Martin Liška <mliska@suse.cz> wrote:
>>>>>>>> On 6/1/19 12:06 AM, Jeff Law wrote:
>>>>>>>>> On 5/22/19 3:13 AM, Martin Liška 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.
>>>>>>>>>>
>>>>>>>>>> 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 ?
>>>>>>>>> Don't we still need to deal with the naked fprintf when there's a
>>>>>>>>> failure.  ie, shouldn't we be raising it with a gcc_assert or somesuch?
>>>>>>>>
>>>>>>>> Good point, I've just adjusted that.
>>>>>>>>
>>>>>>>> Patch can bootstrap on x86_64-linux-gnu and survives regression tests.
>>>>>>>>
>>>>>>>> Ready to be installed?
>>>>>>>
>>>>>>> Ugh, the cselib one is really bad.  But I don't hold my breath for anyone
>>>>>>> fixing it ...
>>>>>>
>>>>>> Yes :D It's been some time and there's no interest in the PR.
>>>>>>
>>>>>>>
>>>>>>> One question - there's unconditional
>>>>>>>
>>>>>>> +         if (m_sanitize_eq_and_hash)
>>>>>>> +           verify (comparable, hash);
>>>>>>>
>>>>>>> which will read a global variable and have (possibly not inline) call
>>>>>>> to verify on a common path even with checking disabled.  So I think
>>>>>>> we want to compile this checking feature out for !CHECKING_P
>>>>>>> or at least make the if __builtin_expect (..., 0), ::verify not
>>>>>>> inlined and marked pure () (thus, !CHECKING_P is simplest ;)).
>>>>>>
>>>>>> Fixed. May I install the patch? The cselib issue can be solved later..
>>>>>
>>>>> You missed the second occurance
>>>>>
>>>>> -  m_searches++;
>>>>> +  if (m_sanitize_eq_and_hash)
>>>>> +    verify (comparable, hash);
>>>>
>>>> Yep ;) I've just install the patch.
>>>
>>> This is breaking my build:
>>>
>>> /home/jason/gt/gcc/hash-map.h:123:71: error: no matching function for
>>> call to ‘hash_table<hash_map<mem_alloc_d\
>>> escription<mem_usage>::mem_location_hash, mem_usage*,
>>> simple_hashmap_traits<default_hash_traits<mem_alloc_desc\
>>> ription<mem_usage>::mem_location_hash>, mem_usage*> >::hash_entry,
>>> false, xcallocator>::hash_table(size_t&, bo\
>>> ol&, bool&, mem_alloc_origin, const char*&, int&, const char*&)’
>>>      : m_table (n, ggc, gather_mem_stats, HASH_MAP_ORIGIN PASS_MEM_STAT) {}
>>>
>>> Looks like this needs to be updated to pass an argument to the new
>>> sanitize_eq_and_hash parameter.
>>>
>>> Jason
>>
>> Sorry for the breakage, I've just fixed that in r272104.
> 
> Thanks.  I'm also seeing a massive compile time hit from this:  A
> constexpr testcase that I've been looking at went from compiling in 13
> seconds to 78 seconds, 6 times as long.  I would expect template-heavy
> code to see similar problems when sanitization is enabled for those
> hash tables.  Could we keep the parameter low or 0 by default, and
> just do occasional sanitize runs with it explicitly enabled?

Makes sense to me. Can you please provide a test-case which I can measure?

Martin

> 
> Jason
>