linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Arvind Sankar <nivedita@alum.mit.edu>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "Arvind Sankar" <nivedita@alum.mit.edu>,
	"Rasmus Villemoes" <linux@rasmusvillemoes.dk>,
	"Nick Desaulniers" <ndesaulniers@google.com>,
	"Dávid Bolvanský" <david.bolvansky@gmail.com>,
	"Eli Friedman" <efriedma@quicinc.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	"Masahiro Yamada" <masahiroy@kernel.org>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Ingo Molnar" <mingo@redhat.com>,
	"Borislav Petkov" <bp@alien8.de>,
	"Michal Marek" <michal.lkml@markovi.net>,
	"Linux Kbuild mailing list" <linux-kbuild@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	"Kees Cook" <keescook@chromium.org>,
	"Tony Luck" <tony.luck@intel.com>,
	"Dmitry Vyukov" <dvyukov@google.com>,
	"Michael Ellerman" <mpe@ellerman.id.au>,
	"Joe Perches" <joe@perches.com>,
	"Joel Fernandes" <joel@joelfernandes.org>,
	"Daniel Axtens" <dja@axtens.net>,
	"Andy Shevchenko" <andriy.shevchenko@linux.intel.com>,
	"Alexandru Ardelean" <alexandru.ardelean@analog.com>,
	"Yury Norov" <yury.norov@gmail.com>,
	"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
	<x86@kernel.org>, "Ard Biesheuvel" <ardb@kernel.org>,
	"Paul E . McKenney" <paulmck@kernel.org>,
	"Daniel Kiper" <daniel.kiper@oracle.com>,
	"Bruce Ashfield" <bruce.ashfield@gmail.com>,
	"Marco Elver" <elver@google.com>,
	"Vamshi K Sthambamkadi" <vamshi.k.sthambamkadi@gmail.com>
Subject: Re: [PATCH 0/4] -ffreestanding/-fno-builtin-* patches
Date: Fri, 21 Aug 2020 15:57:12 -0400	[thread overview]
Message-ID: <20200821195712.GB1475504@rani.riverdale.lan> (raw)
In-Reply-To: <CAHk-=wi8vdb+wo-DACDpSijYfAbCs135YcnnAbRhGJcU+A=-+Q@mail.gmail.com>

On Fri, Aug 21, 2020 at 10:54:57AM -0700, Linus Torvalds wrote:
> On Fri, Aug 21, 2020 at 10:29 AM Arvind Sankar <nivedita@alum.mit.edu> wrote:
> >
> > This one is slightly different from the previous one. The first case is
> > really a call to __builtin_free().
> 
> No, the first case is a disgrace and a compiler bug.
> 
> We've had a situation where gcc complained about a static function
> called "free()", without any header file inclusion, and then
> complained about it not matching its idea of what "free()" is.
> 
> Which is pure and utter garbage.
> 
> It's like you have a local variable "int free", and the compiler says
> "hey, this doesn't match the prototype that I know this name should
> have". It's BS. You just saw the user not just *use* that name, but
> *define* it, and do it in a scope where the complaint is irrelevant
> and stupid, and when we hadn't even included the header that would
> have resulted in conflicts.
> 
> IOW, it's an example of a compiler that thinks "it knows better".
> 
> It's a broken compiler. And it's an example of the kind of breakage
> that compilers absolutely shouldn't do.

That's -Wbuiltin-declaration-mismatch, and can be turned off, and it
won't warn if you have -fno-builtin-free. I don't completely agree with
you, though warning for static functions is a bit overzealous. For an
external function, especially something more obscure like stpcpy(), I
appreciate the warning.

> 
> The second example is from clang doesn't something horribly horribly stupid.

Calm down man :)

> 
> > This one is turning something that wasn't a function call into
> > __builtin_bzero(), and I would hope that no-builtin-bzero would stop it
> > as well. OTOH, the compiler is free to turn it into memset(), just like
> > it could for structure/array initializers.
> 
> The whole "the compiler is free to do X" argument is pure BS. Stop
> repeating that bogus argument.
> 
> Of COURSE a compiler can do whatever the hell it wants.
> 
> That doesn't change the fact that certain things are broken beyond
> words and utterly stupid, and a compiler that does them is a *BAD*
> compiler.
> 
> Turning four stores into a memset() is garbage. Just admit it, instead
> of trying to say that it's allowed.
> 

Look, four stores into memset(), yeah that's a bit weird. I didn't think
you meant "four" literally. But in any case, that has nothing to do with
the topic at hand. It would be just as bad if it was a 16-byte structure
being initialized with an out-of-line memset() call.

But coming back to the actual topic: it is fine if the compiler turns
four stores into __builtin_memset(). A size-16 or -32 __builtin_memset()
will get inlined anyway. There's a lot of garbage here if you look
closely: check out what gcc does to initialize a 7-character array with
zeros at -Os.

  parent reply	other threads:[~2020-08-21 19:57 UTC|newest]

Thread overview: 68+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-17 22:02 [PATCH 0/4] -ffreestanding/-fno-builtin-* patches Nick Desaulniers
2020-08-17 22:02 ` [PATCH 1/4] Makefile: add -fno-builtin-stpcpy Nick Desaulniers
2020-08-17 22:31   ` H. Peter Anvin
2020-08-17 23:36     ` Nick Desaulniers
2020-08-18 19:21     ` Kees Cook
2020-08-18  7:10   ` Ard Biesheuvel
2020-08-18  7:25     ` Greg KH
2020-08-18  7:29       ` Ard Biesheuvel
2020-08-18  7:34         ` Greg KH
2020-08-18 19:23   ` Kees Cook
2020-08-17 22:02 ` [PATCH 2/4] Revert "lib/string.c: implement a basic bcmp" Nick Desaulniers
2020-08-18  5:44   ` Nathan Chancellor
2020-08-18 18:00     ` Nick Desaulniers
2020-08-18 19:24       ` Kees Cook
2020-08-17 22:02 ` [PATCH 3/4] x86/boot: use -fno-builtin-bcmp Nick Desaulniers
2020-08-18 19:24   ` Kees Cook
2020-08-17 22:02 ` [PATCH 4/4] x86: don't build CONFIG_X86_32 as -ffreestanding Nick Desaulniers
2020-08-18 19:24   ` Kees Cook
2021-01-07  0:27   ` Fangrui Song
2022-04-07 15:34   ` [tip: x86/build] x86/build: Don't " tip-bot2 for Nick Desaulniers
2022-04-07 17:01     ` Nick Desaulniers
2022-04-07 22:28       ` Borislav Petkov
2020-08-17 22:44 ` [PATCH 0/4] -ffreestanding/-fno-builtin-* patches H. Peter Anvin
2020-08-18 17:56   ` Nick Desaulniers
2020-08-18 19:02     ` H. Peter Anvin
2020-08-18 19:13       ` Linus Torvalds
2020-08-18 19:25         ` Nick Desaulniers
2020-08-18 19:58           ` Nick Desaulniers
2020-08-19 12:19             ` Clement Courbet
2020-08-18 20:24         ` Arvind Sankar
2020-08-18 20:27           ` Nick Desaulniers
2020-08-18 20:58             ` Nick Desaulniers
2020-08-18 21:41               ` Arvind Sankar
2020-08-18 21:51                 ` Dávid Bolvanský
2020-08-18 21:59                 ` Nick Desaulniers
2020-08-18 22:05                   ` Dávid Bolvanský
2020-08-18 23:22                     ` Nick Desaulniers
2020-08-20 14:56                 ` Rasmus Villemoes
2020-08-20 17:56                   ` Arvind Sankar
2020-08-20 18:05                     ` Dávid Bolvanský
2020-08-20 23:33                     ` Linus Torvalds
2020-08-21 17:29                       ` Arvind Sankar
2020-08-21 17:54                         ` Linus Torvalds
2020-08-21 18:02                           ` Linus Torvalds
2020-08-21 19:14                             ` Arvind Sankar
2020-08-21 19:23                               ` Linus Torvalds
2020-08-21 19:57                           ` Arvind Sankar [this message]
2020-08-21 20:03                             ` Peter Zijlstra
2020-08-21 21:39                             ` Linus Torvalds
2020-08-22  0:12                               ` Nick Desaulniers
2020-08-22 12:20                                 ` David Laight
2020-08-21  6:45                     ` Rasmus Villemoes
2020-08-24 15:57                 ` Masahiro Yamada
2020-08-24 17:34                   ` Arvind Sankar
2020-08-25  7:10                     ` Nick Desaulniers
2020-08-25  7:31                       ` Nick Desaulniers
2020-08-25 12:28                       ` Masahiro Yamada
2020-08-25 14:02                         ` Nick Desaulniers
2020-08-26 13:28                           ` Masahiro Yamada
2020-08-18 21:53               ` David Laight
2020-08-20 22:41               ` H. Peter Anvin
2020-08-20 23:17                 ` Arvind Sankar
2020-08-18 19:35       ` Nick Desaulniers
2020-08-18 22:25 ` Arvind Sankar
2020-08-18 22:59   ` Nick Desaulniers
2020-08-18 23:51     ` Arvind Sankar
2020-08-19  0:20     ` Arvind Sankar
2020-08-19  8:26   ` David Laight

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20200821195712.GB1475504@rani.riverdale.lan \
    --to=nivedita@alum.mit.edu \
    --cc=akpm@linux-foundation.org \
    --cc=alexandru.ardelean@analog.com \
    --cc=andriy.shevchenko@linux.intel.com \
    --cc=ardb@kernel.org \
    --cc=bp@alien8.de \
    --cc=bruce.ashfield@gmail.com \
    --cc=daniel.kiper@oracle.com \
    --cc=david.bolvansky@gmail.com \
    --cc=dja@axtens.net \
    --cc=dvyukov@google.com \
    --cc=efriedma@quicinc.com \
    --cc=elver@google.com \
    --cc=hpa@zytor.com \
    --cc=joe@perches.com \
    --cc=joel@joelfernandes.org \
    --cc=keescook@chromium.org \
    --cc=linux-kbuild@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux@rasmusvillemoes.dk \
    --cc=masahiroy@kernel.org \
    --cc=michal.lkml@markovi.net \
    --cc=mingo@redhat.com \
    --cc=mpe@ellerman.id.au \
    --cc=ndesaulniers@google.com \
    --cc=paulmck@kernel.org \
    --cc=tglx@linutronix.de \
    --cc=tony.luck@intel.com \
    --cc=torvalds@linux-foundation.org \
    --cc=vamshi.k.sthambamkadi@gmail.com \
    --cc=x86@kernel.org \
    --cc=yury.norov@gmail.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).