[cfe-dev] -fcatch-undefined-behavior false positive with readdir()?

[Sean McBride]

Richard,

It prints 8, for every iteration of the loop.  I guess that's correct since the first field of the struct is a uint64_t.

Sean



On Wed, 26 Sep 2012 12:49:38 -0700, Richard Smith said:

>Can you try adding
>
>  printf ("%p %zd\\n", d, _Alignof(*d));
>
>before the line which fails? Is the pointer correctly aligned?
>
>On Wed, Sep 26, 2012 at 12:38 PM, Sean McBride <sean at rogue-research.com>wrote:
>
>> On Wed, 26 Sep 2012 10:40:47 -0400, Joe Ranieri said:
>>
>> >> DIR* dir = opendir("/usr/lib");
>> >> if (dir)
>> >> {
>> >>  struct dirent* d = NULL;
>> >>  while ((d = readdir(dir)) != NULL)
>> >>  {
>> >>   const char* local = d->d_name; // bam!
>> >>   printf ("%s\n", local);
>> >>  }
>> >>  closedir(dir);
>> >> }
>> >>
>> >
>> > *SNIP*
>> >
>> >Just a hunch: is d->d_name an unaligned pointer? We ran into a similar
>> >issue with gethostbyname.
>>
>> Joe,
>>
>> Thanks for your reply.  But I'm afraid I don't follow.  Unaligned with
>> respect to what?  The 'struct dirent' is declared by the system basically
>> like so:
>>
>> #pragma pack()
>> struct dirent {
>>         uint64_t  d_ino;
>>         uint64_t  d_seekoff;
>>         uint16_t  d_reclen;
>>         uint16_t  d_namlen;
>>         uint8_t   d_type;
>>         char      d_name[1024];
>> }
>>
>> Note the 'pragma pack'; is that the alignment you're referring to?  On my
>> system, I don't see any pragma pack with gethostbyname()'s 'struct
>> hostent', what problem did you have with it?
>>
>> I just tried something else: it's not just the d_name field, but accessing
>> any field triggers the SIGILL.