[PATCH 2/2] jmpbuf: Add paddings for target specific usage

[H.J. Lu]

On Mon, Nov 13, 2017 at 11:40 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Mon, Nov 13, 2017 at 8:44 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
>> On Mon, Nov 13, 2017 at 8:34 AM, Florian Weimer <fweimer@redhat.com> wrote:
>>> On 11/13/2017 03:05 PM, H.J. Lu wrote:
>>>>
>>>> On Mon, Nov 13, 2017 at 5:09 AM, Florian Weimer <fweimer@redhat.com>
>>>> wrote:
>>>>>
>>>>> On 11/08/2017 07:27 PM, H.J. Lu wrote:
>>>>>>
>>>>>>
>>>>>> +/* The biggest signal number + 1  */
>>>>>> +#define _JUMP_BUF_SIGSET_NSIG  257
>>>>>> +/* Number of longs to hold all signals.  */
>>>>>> +#define _JUMP_BUF_SIGSET_NWORDS \
>>>>>> +  ((_JUMP_BUF_SIGSET_NSIG - 1 + 7) / (8 * sizeof (unsigned long int)))
>>>>>
>>>>>
>>>>>
>>>>> Where does 257 come from?  65 or 129 I would understand considering the
>>>>> kernel sources, but 257 is odd.
>>>
>>>
>>> Oh.  I'm not sure if we should put this into installed header.
>>>
>>> Maybe we can use a different approach?  Something similar to the pthread
>>> types?  Or just not change the external type at all and just ad some
>>> internal space reuse mechanism?
>>
>> I will see what I can do.
>>
>>> We had problems with people poking at supposedly invisible jmpbuf contents
>>> in the past, and I'm worried that adding even __ members will encourage
>>> that.
>>>
>>>>> I think it would be clearer to hard-code the array sizes and explain why
>>>>> the
>>>>> values where chosen in that way.
>>>>>
>>>>> We also need a test that setprocmask does not read from the previously
>>>>
>>>>
>>>> Did you mean "sigprocmask"?
>>>
>>>
>>> Right.
>>>
>>>>> unused part.  I can move the existing next_to_fault bits to support/ if
>>>>> that
>>>>> would help.
>>>>
>>>>
>>>> Yes, please.
>>>
>>>
>>> Okay, I'll move it to support/ soon.
>>>
>>
>
> Here is the updated patch to add <setjmpP.h>.  I added a test:
>
>   struct support_next_to_fault jmpbuf
>     = support_next_to_fault_allocate (SAVED_MASK_OFFSET + (_NSIG / 8));
>   struct __jmp_buf_tag *sj = (struct __jmp_buf_tag *) jmpbuf.buffer;
>
>   errno = 0;
>   if (sigsetjmp (sj, 1) == 0)
>     {
>       siglongjmp (sj, 1);
>       return EXIT_FAILURE;
>     }
>   if (errno != 0)
>     {
>       printf ("sigsetjmp: %s\n", strerror (errno));
>       return EXIT_FAILURE;
>     }
>
> to verify that __sigprocmask won't read beyond _NSIG / 8.
>
> Does it look OK?
>

This is the updated patch.  Tested with build-many-glibcs.py.

Any other comments?

Thanks.


-- 
H.J.
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