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

[H.J. Lu]

On Wed, Nov 15, 2017 at 3:10 AM, Florian Weimer <fweimer@redhat.com> wrote:
> On 11/14/2017 02:10 PM, H.J. Lu wrote:
>>
>> +static int
>> +do_test (void)
>> +{
>> +  sigjmp_buf sj;
>> +  struct support_next_to_fault sigset_t_buf
>> +    = support_next_to_fault_allocate (SIZEOF_SIGSET_T);
>> +  sigset_t *m_p = (sigset_t *) sigset_t_buf.buffer;
>> +  sigset_t m;
>> +
>> +  sigemptyset (&m);
>> +  memcpy (m_p, &m, SIZEOF_SIGSET_T);
>> +  sigprocmask (SIG_SETMASK, m_p, NULL);
>> +  memcpy (&m, m_p, SIZEOF_SIGSET_T);
>> +  if (sigsetjmp (sj, 0) == 0)
>> +    {
>> +      sigaddset (&m, SIGUSR1);
>> +      memcpy (m_p, &m, SIZEOF_SIGSET_T);
>> +      sigprocmask (SIG_SETMASK, m_p, NULL);
>> +      memcpy (&m, m_p, SIZEOF_SIGSET_T);
>> +      siglongjmp (sj, 1);
>> +      return EXIT_FAILURE;
>> +    }
>> +  sigprocmask (SIG_SETMASK, NULL, m_p);
>> +  memcpy (&m, m_p, SIZEOF_SIGSET_T);
>> +  return sigismember (&m, SIGUSR1) ? EXIT_SUCCESS : EXIT_FAILURE;
>> +}
>
>
> Sorry, I don't understand anymore what this test is supposed to test and
> how.

This tests the reduced __jmp_buf_sigset_t used by __saved_mask is
bigger than sigset expected by kernel.

> To be honest, I don't like how you inject the internal definition of
> jmp_buf.  Is this the way we do it for the nptl types?

I only need to make some room in

/* Calling environment, plus possibly a saved signal mask.  */
struct __jmp_buf_tag
  {
    /* NOTE: The machine-dependent definitions of `__sigsetjmp'
       assume that a `jmp_buf' begins with a `__jmp_buf' and that
       `__mask_was_saved' follows it.  Do not move these members
       or add others before it.  */
    __jmp_buf __jmpbuf; /* Calling environment.  */
    int __mask_was_saved; /* Saved the signal mask?  */
    __sigset_t __saved_mask; /* Saved signal mask.  */
  };

for target specific purpose.   I changed it to

struct __jmp_buf_tag
  {
    /* NOTE: The machine-dependent definitions of `__sigsetjmp'
       assume that a `jmp_buf' begins with a `__jmp_buf' and that
       `__mask_was_saved' follows it.  Do not move these members
       or add others before it.  */
    __jmp_buf __jmpbuf; /* Calling environment.  */
    int __mask_was_saved; /* Saved the signal mask?  */
    union
    {
    __sigset_t __saved_mask_compat;
    struct
      {
__jmp_buf_sigset_t __saved_mask;
/* Paddings for architecture specific usage.  */
unsigned long int __padding[12];
      } __saved;
    }  __saved_mask;
  };

#define __saved_mask __saved_mask.__saved.__saved_mask

I did only to  __sigset_t  in __jmp_buf_tag and this test verifies that the size
of __jmp_buf_sigset_t works with sigprocmask.

Are you suggesting we make some room in __sigset_t directly?  This will
require very extensive changes. If not, what do you exactly suggest?

> I think you should check _JUMP_BUF_SIGSET_NSIG against a kernel constant
> (_NSIGS?) somewhere.

There is a _Static_assert in include/setjmp.h.  But it isn't triggered.  This
updated patch moves it to sysdeps/unix/sysv/linux/__saved_mask.h.   Now
I got

../sysdeps/unix/sysv/linux/__saved_mask.h:32:1: error: static
assertion failed: "size of ___saved_mask < size of
__sigprocmask_sigset_t"
 _Static_assert (sizeof (___saved_mask) >= sizeof (__sigprocmask_sigset_t),

if __jmp_buf_sigset_t is too small.

-- 
H.J.
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