From: George Koehler <kernigh@gmail.com>
Subject: Re: new warning in make
To: Marc Espie <marc.espie.openbsd@gmail.com>
Cc: millert@openbsd.org, tech@openbsd.org
Date: Fri, 26 Sep 2025 00:55:59 -0400

On Thu, 25 Sep 2025 11:35:28 +0200
Marc Espie <marc.espie.openbsd@gmail.com> wrote:

> cc now warns over arch.c
> /usr/src/usr.bin/make/arch.c:839:3: warning: 'snprintf' will always be truncated; specified size is 12, but format string expands to at least 13 [-Wformat-truncation]
>   839 |                 snprintf(arHeader.ar_date, sizeof(arHeader.ar_date),
>       |                 ^
> 
> 
> Pretty sure it's correct, considering that snprintf will truncate with a 0.
> 
> Printing to a temp buffer and copying only the string ought to fix it
> if I'm not mistaken.

Your diff is correct, but while we are here, I wonder if it should be
"%-12lld" and (long long)time(NULL)?

(Minor detail: maybe add an empty line under "char temp".)

I tried to run the code, but the archive feature in make(1) is so
broken that I had trouble reaching it.  First, make(1) opens the wrong
archive.  I tried to touch a target named "stuff.a(one)", expecting it
to open an archive named "stuff.a", but it instead opened an archive
named "stuff.a(one)".  Second, make(1) can't find members if the
archive has a symbol table.  I archived a text file with no symbols,

$ cat Makefile
stuff.a(one): one
	ar rcU stuff.a one
	ar rcU "stuff.a(one)" one

Then make -t ignored "stuff.a" and touched "one" in "stuff.a(one)" and
corrupted the time with a '\0', unless this diff fixed the truncation.

I'm in no hurry to fix the name and symbol problems, as I do not use
the archive feature.
--gkoehler

> Index: arch.c
> ===================================================================
> RCS file: /vide/cvs/src/usr.bin/make/arch.c,v
> diff -u -p -r1.94 arch.c
> --- arch.c	4 Sep 2023 11:35:11 -0000	1.94
> +++ arch.c	25 Sep 2025 09:33:07 -0000
> @@ -836,8 +836,9 @@ ArchTouch(const char *archive, const cha
>  
>  	arch = ArchFindMember(archive, member, &arHeader, "r+");
>  	if (arch != NULL) {
> -		snprintf(arHeader.ar_date, sizeof(arHeader.ar_date),
> -		    "%-12ld", (long) time(NULL));
> +		char temp[sizeof(arHeader.ar_date)+1];
> +		snprintf(temp, sizeof(temp), "%-12ld", (long) time(NULL));
> +		memcpy(arHeader.ar_date, temp, sizeof(arHeader.ar_date));
>  		if (fseek(arch, -sizeof(struct ar_hdr), SEEK_CUR) == 0)
>  			(void)fwrite(&arHeader, sizeof(struct ar_hdr), 1, arch);
>  		fclose(arch);
>