[systemd-devel] [PATCH] journal: fix assert against (theoretical) undefined behavior

[Shawn Landden]

On Mon, Dec 16, 2013 at 10:36 AM, Lennart Poettering
<lennart at poettering.net> wrote:
> On Mon, 16.12.13 09:20, Shawn Landden (shawn at churchofgit.com) wrote:
>
>> While all the libc implementations I know return NULL when memchr's size
>> parameter is 0:
>>
>> C11 7.24.1p2: Where an argument declared as "size_t n" specifies the length
>> of the array for a function, n can have the value zero on a call to that
>> function. Unless explicitly stated otherwise in the description of a
>> particular function in this subclause, pointer arguments on such a call
>> shall still have valid values, as described in 7.1.4. On such a call, a
>> function that locates a character finds no occurrence, a function that
>> compares two character sequences returns zero, and a function that copies
>> characters copies zero characters.
>>
>> see http://llvm.org/bugs/show_bug.cgi?id=18247
>
> Hmm? But what does that have to do with the requirements we make on our
> own internal functions?
Well, it makes clang's scan-build shut up :), which is how i initially
came across it.
>
>> ---
>>  src/journal/journal-file.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/src/journal/journal-file.c b/src/journal/journal-file.c
>> index 4009b29..59b2829 100644
>> --- a/src/journal/journal-file.c
>> +++ b/src/journal/journal-file.c
>> @@ -956,7 +956,7 @@ static int journal_file_append_data(
>>          const void *eq;
>>
>>          assert(f);
>> -        assert(data || size == 0);
>> +        assert(data);
>>
>>          hash = hash64(data, size);
>>
>
>
> Lennart
>
> --
> Lennart Poettering, Red Hat
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