Subject: Re: [PATCH] git-compat-util: avoid redefining system function names

From: Bagas Sanjaya <[email-masked]>
Date: Sat, 3 Dec 2022 15:02:05 +0700

On Fri, Dec 02, 2022 at 06:05:38AM -0500, Jeff King wrote:
> -- >8 --
> Subject: [PATCH] git-compat-util: undefine system names before redeclaring
>  them
> 
> When we define a macro to point a system function (e.g., flockfile) to
> our custom wrapper, we should make sure that the system did not already
> define it as a macro. This is rarely a problem, but can cause
> compilation failures if both of these are true:
> 
>   - we decide to define our own wrapper even though the system provides
>     the function; we know this happens at least with uclibc, which may
>     declare flockfile, etc, without _POSIX_THREAD_SAFE_FUNCTIONS
> 
>   - the system version is declared as a macro; we know this happens at
>     least with uclibc's version of getc_unlocked()
> 
> So just handling getc_unlocked() would be sufficient to deal with the
> real-world case we've seen. But since it's easy to do, we may as well be
> defensive about the other macro wrappers added in the previous patch.
> 
> Signed-off-by: Jeff King <[email-masked]>
> ---
> There may be other similar cases lurking throughout the code base, but I
> don't think it's worth anybody's time to go looking for them. If one of
> them triggers on a real platform, we can deal with it then.
> 
>  git-compat-util.h | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/git-compat-util.h b/git-compat-util.h
> index 83ec7b7941..76e4b11131 100644
> --- a/git-compat-util.h
> +++ b/git-compat-util.h
> @@ -346,6 +346,7 @@ static inline int git_setitimer(int which UNUSED,
>  				struct itimerval *newvalue UNUSED) {
>  	return 0; /* pretend success */
>  }
> +#undef setitimer
>  #define setitimer(which,value,ovalue) git_setitimer(which,value,ovalue)
>  #endif
>  
> @@ -1480,6 +1481,9 @@ static inline void git_funlockfile(FILE *fh UNUSED)
>  {
>  	; /* nothing */
>  }
> +#undef flockfile
> +#undef funlockfile
> +#undef getc_unlocked
>  #define flockfile(fh) git_flockfile(fh)
>  #define funlockfile(fh) git_funlockfile(fh)
>  #define getc_unlocked(fh) getc(fh)

The warnings gone away, thanks!

For this patch and the previous one [1],

Tested-by: Bagas Sanjaya <[email-masked]>

[1]: https://lore.kernel.org/git/[email-masked]/

-- 
An old man doll... just what I always wanted! - Clara