diff mbox

[genattrtab] Fix memory corruption, allocate enough memory for all bypassed reservations

Message ID 539EC327.2040004@arm.com
State New
Headers show

Commit Message

Kyrylo Tkachov June 16, 2014, 10:12 a.m. UTC 
On 13/06/14 16:51, Jeff Law wrote:
> On 06/13/14 03:56, Kyrill Tkachov wrote:
>> Hi all,
>>
>> I noticed a memory corruption bug while adding some scheduler bypasses
>> in the arm backend.
>> genattrtab would segfault while processing the bypasses. Valgrind
>> confirmed this.
>>
>> The problem is that when processing the bypassed reservations,
>> make_automaton_pairs allocates memory in proportion to the number of
>> defined bypasses rather than the number of bypassed reservations. This
>> means that if the number of bypassed reservations is sufficiently larger
>> than the number of bypasses, the loop will overwrite unallocated memory.
>>
>> I also observed this effect on aarch64, but there was no segfault there,
>> presumably because the number of reservations in aarch64 is much smaller
>> than arm at the moment (we only use two pipeline descriptions in aarch64).
>>
>> This patch fixes that and valgrind confirms that there's no out of
>> bounds accesses now.
>>
>> Bootstrapped and tested arm-none-linux-gnueabihf,
>> aarch64-none-linux-gnu, x86_64-linux.
>>
>> Ok for trunk?
>>
>> Thanks,
>> Kyrill
>>
>> 2014-06-13  Kyrylo Tkachov <kyrylo.tkachov@arm.com>
>>
>>       * genattrtab.c (n_bypassed): New variable.
>>       (process_bypasses): Initialise n_bypassed.
>>       Count number of bypassed reservations.
>>       (make_automaton_attrs): Allocate space for bypassed reservations
>>       rather than number of bypasses.
>>
>> genattrtab-bypasses.patch
>>
>>
>> diff --git a/gcc/genattrtab.c b/gcc/genattrtab.c
>> index c5ce51c..2b6b3ce 100644
>> --- a/gcc/genattrtab.c
>> +++ b/gcc/genattrtab.c
>> @@ -4766,6 +4766,7 @@ struct bypass_list
>>
>>    static struct bypass_list *all_bypasses;
>>    static size_t n_bypasses;
>> +static size_t n_bypassed;
>>
>>    static void
>>    gen_bypass_1 (const char *s, size_t len)
>> @@ -4811,12 +4812,19 @@ process_bypasses (void)
>>      struct bypass_list *b;
>>      struct insn_reserv *r;
>>
>> +  n_bypassed = 0;
>> +
>>      /* The reservation list is likely to be much longer than the bypass
>>         list.  */
>>      for (r = all_insn_reservs; r; r = r->next)
>>        for (b = all_bypasses; b; b = b->next)
>>          if (fnmatch (b->pattern, r->name, 0) == 0)
>> -	r->bypassed = true;
>> +        {
>> +          if (!r->bypassed)
>> +            n_bypassed++;
>> +
>> +          r->bypassed = true;
>> +        }
>>    }
> Might as well go ahead and put the r->bypassed = true assignment inside
> the if (!r->bypassed) conditional.  It probably doesn't matter in terms
> of real performance, but it's easy to do.  In fact, once you hit that
> case ISTM the inner loop is pointless.  So I think it ought to look like:
>
>     /* The reservation list is likely to be much longer than the bypass
>        list.  */
>     for (r = all_insn_reservs; r; r = r->next)
>       for (b = all_bypasses; b; b = b->next)
>         if (fnmatch (b->pattern, r->name, 0) == 0)
> 	{
> 	  r->bypassed = true;
> 	  n_bypassed++;
> 	  break;
> 	}
>
>
> Or am I missing something?

Doh, you're right. I did consider it but for some reason thought we 
might want to iterate over all of the bypasses anyway. Breaking out 
seems good.

How about this?
Tested on arm and aarch64 and confirmed with valgrind that no out of 
bounds accesses occur.
I kicked off an x86_64 bootstrap but don't expect any problems.

Thanks,
Kyrill

Comments

Jeff Law June 16, 2014, 4:39 p.m. UTC | #1 
On 06/16/14 04:12, Kyrill Tkachov wrote:

>
> Doh, you're right. I did consider it but for some reason thought we
> might want to iterate over all of the bypasses anyway. Breaking out
> seems good.
>
> How about this?
> Tested on arm and aarch64 and confirmed with valgrind that no out of
> bounds accesses occur.
> I kicked off an x86_64 bootstrap but don't expect any problems.
>
> Thanks,
> Kyrill
>
> genattrtab-bypasses.patch
>
>
> commit 676b85f7a7cc1446482334dcaad457ac328875a8
> Author: Kyrylo Tkachov<kyrylo.tkachov@arm.com>
> Date:   Fri Jun 13 11:09:57 2014 +0100
>
>      [genattrtab] Fix memory corruption with bypasses
I'm an idiot.  n_bypassed is used to size the vector, so you do have to 
walk the entire list.

Jeff
Kyrylo Tkachov June 17, 2014, 8:12 a.m. UTC | #2 
On 16/06/14 17:39, Jeff Law wrote:
> On 06/16/14 04:12, Kyrill Tkachov wrote:
>
>> Doh, you're right. I did consider it but for some reason thought we
>> might want to iterate over all of the bypasses anyway. Breaking out
>> seems good.
>>
>> How about this?
>> Tested on arm and aarch64 and confirmed with valgrind that no out of
>> bounds accesses occur.
>> I kicked off an x86_64 bootstrap but don't expect any problems.
>>
>> Thanks,
>> Kyrill
>>
>> genattrtab-bypasses.patch
>>
>>
>> commit 676b85f7a7cc1446482334dcaad457ac328875a8
>> Author: Kyrylo Tkachov<kyrylo.tkachov@arm.com>
>> Date:   Fri Jun 13 11:09:57 2014 +0100
>>
>>       [genattrtab] Fix memory corruption with bypasses
> I'm an idiot.  n_bypassed is used to size the vector, so you do have to
> walk the entire list.

AFAICS in the loop in process_bypasses we want to count all the 
reservations which have a bypass matching them. Once a reservation is 
matched with a bypass it should be safe to break out of the inner loop 
(over the bypasses), even if two bypasses match a reservation we only 
want to count the reservation once.

So I think the 2nd version of the patch is good

Thanks,
Kyrill
>
> Jeff
>
>
>
>
Jeff Law June 17, 2014, 8:26 p.m. UTC | #3 
On 06/17/14 02:12, Kyrill Tkachov wrote:
>
> On 16/06/14 17:39, Jeff Law wrote:
>> On 06/16/14 04:12, Kyrill Tkachov wrote:
>>
>>> Doh, you're right. I did consider it but for some reason thought we
>>> might want to iterate over all of the bypasses anyway. Breaking out
>>> seems good.
>>>
>>> How about this?
>>> Tested on arm and aarch64 and confirmed with valgrind that no out of
>>> bounds accesses occur.
>>> I kicked off an x86_64 bootstrap but don't expect any problems.
>>>
>>> Thanks,
>>> Kyrill
>>>
>>> genattrtab-bypasses.patch
>>>
>>>
>>> commit 676b85f7a7cc1446482334dcaad457ac328875a8
>>> Author: Kyrylo Tkachov<kyrylo.tkachov@arm.com>
>>> Date:   Fri Jun 13 11:09:57 2014 +0100
>>>
>>>       [genattrtab] Fix memory corruption with bypasses
>> I'm an idiot.  n_bypassed is used to size the vector, so you do have to
>> walk the entire list.
>
> AFAICS in the loop in process_bypasses we want to count all the
> reservations which have a bypass matching them. Once a reservation is
> matched with a bypass it should be safe to break out of the inner loop
> (over the bypasses), even if two bypasses match a reservation we only
> want to count the reservation once.
>
> So I think the 2nd version of the patch is good
OK.  APproved.

jeff
diff mbox

Patch

commit 676b85f7a7cc1446482334dcaad457ac328875a8
Author: Kyrylo Tkachov <kyrylo.tkachov@arm.com>
Date:   Fri Jun 13 11:09:57 2014 +0100

    [genattrtab] Fix memory corruption with bypasses

diff --git a/gcc/genattrtab.c b/gcc/genattrtab.c
index c5ce51c..9db2ade 100644
--- a/gcc/genattrtab.c
+++ b/gcc/genattrtab.c
@@ -4766,6 +4766,7 @@  struct bypass_list
 
 static struct bypass_list *all_bypasses;
 static size_t n_bypasses;
+static size_t n_bypassed;
 
 static void
 gen_bypass_1 (const char *s, size_t len)
@@ -4811,12 +4812,18 @@  process_bypasses (void)
   struct bypass_list *b;
   struct insn_reserv *r;
 
+  n_bypassed = 0;
+
   /* The reservation list is likely to be much longer than the bypass
      list.  */
   for (r = all_insn_reservs; r; r = r->next)
     for (b = all_bypasses; b; b = b->next)
       if (fnmatch (b->pattern, r->name, 0) == 0)
-	r->bypassed = true;
+        {
+          n_bypassed++;
+          r->bypassed = true;
+          break;
+        }
 }
 
 /* Check that attribute NAME is used in define_insn_reservation condition
@@ -5075,7 +5082,7 @@  make_automaton_attrs (void)
       process_bypasses ();
 
       byps_exp = rtx_alloc (COND);
-      XVEC (byps_exp, 0) = rtvec_alloc (n_bypasses * 2);
+      XVEC (byps_exp, 0) = rtvec_alloc (n_bypassed * 2);
       XEXP (byps_exp, 1) = make_numeric_value (0);
       for (decl = all_insn_reservs, i = 0;
 	   decl;