From: Marc Espie <marc.espie.openbsd@gmail.com>
Subject: Re: new warning in make
To: George Koehler <kernigh@gmail.com>
Cc: millert@openbsd.org, tech@openbsd.org
Date: Fri, 26 Sep 2025 09:28:13 +0200

On Fri, Sep 26, 2025 at 12:55:59AM -0400, George Koehler wrote:
> 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

Likewise, but silencing a warning that's correct is the best way to go.

Can you commit this (eventually with an extra blank line) and then
we'll bike-shed ? :D

> > 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);
> > 
>