Re: [PATCH] sh: use sizeof() in memchunk_cmdline_override

[Thorsten Blum <thorsten.blum@linux.dev>]

On Fri, Apr 24, 2026 at 01:15:20PM +0200, Thorsten Blum wrote:
> On Fri, Apr 24, 2026 at 01:05:48PM +0200, Geert Uytterhoeven wrote:
> > Hi Thorsten,
> > 
> > On Thu, 23 Apr 2026 at 14:10, Thorsten Blum <thorsten.blum@linux.dev> wrote:
> > > Replace the hard-coded string length with 'sizeof("memchunk.") - 1' and
> > > remove the comment.
> > >
> > > Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
> > 
> > Thanks for your patch!
> > 
> > > --- a/arch/sh/mm/consistent.c
> > > +++ b/arch/sh/mm/consistent.c
> > > @@ -23,7 +23,7 @@ static void __init memchunk_cmdline_override(char *name, unsigned long *sizep)
> > >         int k = strlen(name);
> > >
> > >         while ((p = strstr(p, "memchunk."))) {
> > > -               p += 9; /* strlen("memchunk.") */
> > > +               p += sizeof("memchunk.") - 1;
> > 
> > Can't you just use strlen() instead, i.e. won't the compiler optimize
> > that into a constant?
> 
> That only works if ARCH_HAS_FORTIFY_SOURCE is selected, which is not the
> case for arch/sh. Otherwise I would have used strlen().

More concretely, because __HAVE_ARCH_STRLEN is set in
arch/sh/include/asm/string_32.h, strlen() resolves to the arch-specific
assembly implementation in arch/sh/lib/strlen.S.

However, constant folding is only guaranteed when calls go through
__builtin_strlen(), e.g. via the wrapper in linux/fortify-string.h,
which SH does not use with dreamcast_defconfig.

I also checked the disassembly, and sh4-linux-gnu-gcc (Debian 14.2.0-19)
did not optimize it into a constant.