linux-kernel - Re: [PATCH 06/10] fortify: replace __is_constexpr() by is

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Message-ID: <CAMZ6RqJMXKaa_xDcyweGwb+FqvANrpvrkRvnjh6_s-J1ApVmaA@mail.gmail.com>
Date: Fri, 6 Dec 2024 00:53:56 +0900
From: Vincent Mailhol <mailhol.vincent@...adoo.fr>
To: David Laight <David.Laight@...lab.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>, 
	Luc Van Oostenryck <luc.vanoostenryck@...il.com>, Nathan Chancellor <nathan@...nel.org>, 
	Nick Desaulniers <ndesaulniers@...gle.com>, Bill Wendling <morbo@...gle.com>, 
	Justin Stitt <justinstitt@...gle.com>, Yury Norov <yury.norov@...il.com>, 
	Rasmus Villemoes <linux@...musvillemoes.dk>, Kees Cook <kees@...nel.org>, 
	"Gustavo A. R. Silva" <gustavoars@...nel.org>, Jani Nikula <jani.nikula@...ux.intel.com>, 
	Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>, Rodrigo Vivi <rodrigo.vivi@...el.com>, 
	Tvrtko Ursulin <tursulin@...ulin.net>, David Airlie <airlied@...il.com>, 
	Simona Vetter <simona@...ll.ch>, Suzuki K Poulose <suzuki.poulose@....com>, 
	Mike Leach <mike.leach@...aro.org>, James Clark <james.clark@...aro.org>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, 
	Rikard Falkeborn <rikard.falkeborn@...il.com>, 
	Martin Uecker <Martin.Uecker@....uni-goettingen.de>, 
	"linux-sparse@...r.kernel.org" <linux-sparse@...r.kernel.org>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, 
	"llvm@...ts.linux.dev" <llvm@...ts.linux.dev>, 
	"linux-hardening@...r.kernel.org" <linux-hardening@...r.kernel.org>, 
	"intel-gfx@...ts.freedesktop.org" <intel-gfx@...ts.freedesktop.org>, 
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>, 
	"coresight@...ts.linaro.org" <coresight@...ts.linaro.org>, 
	"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 06/10] fortify: replace __is_constexpr() by is_const() in strlen()

On Thu. 5 Dec. 2024 at 03:58, David Laight <David.Laight@...lab.com> wrote:
> From: Vincent Mailhol
> > Sent: 02 December 2024 17:33
> >
> > From: Vincent Mailhol <mailhol.vincent@...adoo.fr>
> >
> > is_const() is a one to one replacement of __is_constexpr(). Do the
> > replacement so that __is_constexpr() can be removed.
> >
> > Signed-off-by: Vincent Mailhol <mailhol.vincent@...adoo.fr>
> > ---
> >  include/linux/fortify-string.h | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/linux/fortify-string.h b/include/linux/fortify-string.h
> > index 0d99bf11d260a3482bbe46e35c7553c0ccfb8b94..e3f2f772c5439ef71eb4a904b4ce27956bc69743 100644
> > --- a/include/linux/fortify-string.h
> > +++ b/include/linux/fortify-string.h
> > @@ -254,8 +254,8 @@ __FORTIFY_INLINE __kernel_size_t strnlen(const char * const POS p, __kernel_size
> >   * Returns number of characters in @p (NOT including the final NUL).
> >   *
> >   */
> > -#define strlen(p)                                                    \
> > -     __builtin_choose_expr(__is_constexpr(__builtin_strlen(p)),      \
> > +#define strlen(p)                                            \
> > +     __builtin_choose_expr(is_const(__builtin_strlen(p)),    \
> >               __builtin_strlen(p), __fortify_strlen(p))
>
> I'm sure Linus suggested a way of doing that without replicating
> the __builtin_strlen().
>
> Indeed it may be valid to do:
>         len = __builtin_strlen(p);
>         __builtin_constant_p(len) ? len : __fortify_strlen(p);

Then, wouldn't it be better for strlen() to be an inline function
instead of a macro?

  __FORTIFY_INLINE __kernel_size_t strlen(const char *p)
  {
          __kernel_size_t ret = __builtin_strlen(p);

          if (__builtin_constant_p(ret))
                  return ret;
          return __fortify_strlen(p);
  }

I tested it and it worked on an allyesconfig. So if I receive no
objections, strlen() will become an inline function in v2.


Yours sincerely,
Vincent Mailhol