On Mon, Mar 19, 2018 at 05:56:11PM +0000, Ramsay Jones wrote:
> For the purposes of this discussion, the ce_write_entry() function has
> three code blocks of interest, that look like so:
>
> /* block #1 */
> if (ce->ce_flags & CE_STRIP_NAME) {
> saved_namelen = ce_namelen(ce);
> ce->ce_namelen = 0;
> }
>
> /* block #2 */
> /*
> * several code blocks that contain, among others, calls
> * to copy_cache_entry_to_ondisk(ondisk, ce);
> */
>
> /* block #3 */
> if (ce->ce_flags & CE_STRIP_NAME) {
> ce->ce_namelen = saved_namelen;
> ce->ce_flags &= ~CE_STRIP_NAME;
> }
>
> The warning implies that gcc thinks it is possible that the first
> block is not entered, the calls to copy_cache_entry_to_ondisk()
> could toggle the CE_STRIP_NAME flag on, thereby entering block #3
> with saved_namelen unset. However, the copy_cache_entry_to_ondisk()
> function does not write to ce->ce_flags (it only reads). gcc could
> easily determine this, since that function is local to this file,
> but it obviously doesn't.
Weird. It seems like it would be pretty easy for it to know that we
don't write the flags field at all. But I also don't see any other thing
that would fool the compiler.
> In order to suppress this warning, we make it clear to the reader
> (human and compiler), that block #3 will only be entered when the
> first block has been entered, by introducing a new 'stripped_name'
> boolean variable. We also take the opportunity to change the type
> of 'saved_namelen' to 'unsigned int' to match ce->ce_namelen.
These probably both ought to be size_t, but it makes sense to match
ce_namelen for now.
> diff --git a/read-cache.c b/read-cache.c
> index 2eb81a66b..49607ddcd 100644
> --- a/read-cache.c
> +++ b/read-cache.c
> @@ -2104,13 +2104,15 @@ static int ce_write_entry(git_SHA_CTX *c, int fd, struct cache_entry *ce,
> struct strbuf *previous_name, struct ondisk_cache_entry *ondisk)
> {
> int size;
> - int saved_namelen = saved_namelen; /* compiler workaround */
> int result;
> + unsigned int saved_namelen;
> + int stripped_name = 0;
Maybe too clever, but I think you could just do:
unsigned int saved_namelen = 0;
...
saved_namelen = ce_namelen(ce);
...
if (saved_namelen)
ce->ce_namelen = saved_namelen;
ce->ce_flags &= ~CE_STRIP_NAME;
the zero-length name case (if that's even legal) would work out the
same.
That probably falls under the category of bikeshedding, though.
-Peff
