Re: [PATCH, libgfortran] PR 60324 Unbounded stack allocations in libgfortran

[Cesar Philippidis]

On 11/14/2014 10:01 PM, Janne Blomqvist wrote:
> On Fri, Nov 14, 2014 at 11:02 PM, Tobias Burnus <bur...@net-b.de> wrote:
>> Cesar Philippidis wrote:
>>>
>>> On 11/13/2014 02:32 AM, Janne Blomqvist wrote:
>>> I hit an error when building intrinsics/random.c:
>>>    error: expression in static assertion is not constant
>>> Joseph told me that static const variables cannot be used in constant
>>> expressions in C, so I've replaced the _Static_assert with a regular
>>> assert. Are you using g++ to build libgfortran?
>>
>>
>> I wonder why you are seeing this while others aren't.
> 
> Yeah, I wonder the same?

It does seem strange. Maybe that function isn't necessary for all
targets? I've attached a reduced test case if anyone is interested in
it. That error should show up with "gcc random.c".

>>> I don't have a good baseline test this patch thoroughly, but at least I
>>> can bootstrap gcc without it failing in libgfortran. Is this OK for
>>> mainline and/or could someone see if it causes any regressions?
>>
>>
>> I think instead of doing a run-time check I'd prefer something like the
>> following, keeping the compile-time assert.
>>
>> --- a/libgfortran/intrinsics/random.c
>> +++ b/libgfortran/intrinsics/random.c
>> @@ -253 +253 @@ static GFC_UINTEGER_4 kiss_default_seed[] = {
>> -static const GFC_INTEGER_4 kiss_size =
>> sizeof(kiss_seed)/sizeof(kiss_seed[0]);
>> +#define KISS_SIZE ((GFC_INTEGER_4) (sizeof(kiss_seed)/sizeof(kiss_seed[0]))
>>
>> (plus s/kiss_size/KISS_SIZE/ changes in the code.)
>>
>> Janne, what do you think?
> 
> I like it. With this, you can also get rid of the assert and the newly
> introduced KISS_MAX_SIZE macro, and just make the seed array the
> correct size, as was originally done (with a VLA). Consider such a
> patch pre-approved.

Thanks for fixing this!

Cesar


#include <stdint.h>

typedef int32_t GFC_INTEGER_4;
typedef uint32_t GFC_UINTEGER_4;

static const GFC_UINTEGER_4 kiss_seed[] = {
  123456789, 362436069, 521288629, 316191069,
  987654321, 458629013, 582859209, 438195021,

  573658661, 185639104, 582619469, 296736107

};

static const GFC_INTEGER_4 kiss_size = sizeof(kiss_seed)/sizeof(kiss_seed[0]);

int
main ()
{
#define KISS_MAX_SIZE 12
  unsigned char seed[4 * 12];

  _Static_assert (kiss_size <= 12, "kiss_size must <= KISS_MAX_SIZE");
  //static_assert (kiss_size <= 12, "kiss_size must <= KISS_MAX_SIZE");

  return 0;
}