Re: [PATCH 5/5] xdiff: NUL-terminate buffers read by read_mmfile()

> On Tue, Sep 29, 2026 at 02:55:04AM -0400, Jeff King wrote:
>> Since an mmfile_t is a ptr/len pair, our read_mmfile() allocates exactly
>> the number of bytes we claim to store. But in many other places in Git,
>> we add an extra NUL "just in case", which can help avoid read overruns
>> due to off-by-ones or the use of string functions.
>> 
>> I don't know of any path that would benefit from this, but I noticed it
>> while converting ll_ext_merge() to use read_mmfile(), since its original
>> code did add a NUL byte (even though I cannot find any case where it
>> would have mattered). Let's teach read_mmfile() to add this defensive
>> NUL; it probably doesn't help anything, but nor should it hurt.
>> 
>> Note that the matching read_mmblob() doesn't need the same treatment.
>> Its buffers already have a NUL from the object-reading code (which uses
>> the same defensive trick).
>> 
>> As a bonus, we can get rid of the hack in read_mmfile() to handle empty
>> files by allocating a single byte.
>> 
>> Signed-off-by: Jeff King <peff@peff.net>
>> ---
>> This one is obviously optional, which is why I put it last.
>> ...
>> -	ptr->ptr = xmalloc(sz ? sz : 1);
>> +	ptr->ptr = xmallocz(sz);
>
> I was staring at this code a while before I noticed the added `z` at the
> end of this function.