Jeff King wrote:
> What I missed is that copy_begin and copy_end here are actually size_t
> variables, not the pointers. Sorry for the confusion, and here's an
> updated version of the patch with this paragraph amended (the patch
> itself is identical):
Subtle. The world makes more sense now. Thanks for figuring it out.
> -- >8 --
> Subject: [PATCH] config: avoid "write_in_full(fd, buf, len) < len" pattern
>
> The return type of write_in_full() is a signed ssize_t,
> because we may return "-1" on failure (even if we succeeded
> in writing some bytes). But "len" itself is may be an
> unsigned type (the function takes a size_t, but of course we
> may have something else in the calling function). So while
> it seems like:
>
> if (write_in_full(fd, buf, len) < len)
> die_errno("write error");
>
> would trigger on error, it won't if "len" is unsigned. The
> compiler sees a signed/unsigned comparison and promotes the
> signed value, resulting in (size_t)-1, the highest possible
> size_t (or again, whatever type the caller has). This cannot
> possibly be smaller than "len", and so the conditional can
> never trigger.
>
> I scoured the code base for cases of this, but it turns out
> that these two in git_config_set_multivar_in_file_gently()
> are the only ones. Here our "len" is the difference between
> two size_t variables, making the result an unsigned size_t.
> We can fix this by just checking for a negative return value
> directly, as write_in_full() will never return any value
> except -1 or the full count.
[...]
> Reported-by: demerphq <demer...@gmail.com>
> Signed-off-by: Jeff King <p...@peff.net>
> ---
For what it's worth,
Reviewed-by: Jonathan Nieder <jrnie...@gmail.com>
Thank you.
Compilers' signed/unsigned comparison warning can be noisy, but I'm
starting to feel it's worth the suppression noise to turn it on when
DEVELOPER=1 anyway. What do you think? Is there a way to turn it on
selectively for certain functions on the LHS (like read() and write()
style functions)?
Sincerely,
Jonathan
