From: Linus Torvalds <torvalds@linux-foundation.org>
To: Nick Desaulniers <ndesaulniers@google.com>
Cc: Masahiro Yamada <masahiroy@kernel.org>,
Kees Cook <keescook@chromium.org>,
Josef Bacik <josef@toxicpanda.com>, Jens Axboe <axboe@kernel.dk>,
Rasmus Villemoes <linux@rasmusvillemoes.dk>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Sasha Levin <sashal@kernel.org>,
llvm@lists.linux.dev, stable <stable@vger.kernel.org>,
Arnd Bergmann <arnd@kernel.org>,
Naresh Kamboju <naresh.kamboju@linaro.org>,
Nathan Chancellor <nathan@kernel.org>,
Stephen Rothwell <sfr@canb.auug.org.au>,
Pavel Machek <pavel@ucw.cz>
Subject: Re: [PATCH 5.10] overflow.h: use new generic division helpers to avoid / operator
Date: Tue, 14 Sep 2021 12:52:55 -0700 [thread overview]
Message-ID: <CAHk-=wiydA=Oay+NB2m2ewCHpPEcoU51qPFrzsekFoPu7QPtuw@mail.gmail.com> (raw)
In-Reply-To: <CAKwvOdnYdhkiYZdRvJSzAA78bMD3aS9oayc4SeeANddgxUsMLQ@mail.gmail.com>
On Tue, Sep 14, 2021 at 12:12 PM Nick Desaulniers
<ndesaulniers@google.com> wrote:
>
> On Tue, Sep 14, 2021 at 11:55 AM Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
> >
> > Btw, these kinds of issues is exactly why I've been hardnosed about
> > 64-bit divides for decades. 64-bit divides on 32-bit machines are
> > *expensive*. It's why I don't like saying "just use '/' and we'll pick
> > up the routines from libgcc".
>
> I was going to ask about the history there; not to derail the thread
> further, but this is a question whose answer is important to me.
>
> Are the helpers from libgcc insufficient? W
No. The helpers from libgcc are *overly* sufficient.
The reason we strive to avoid libgcc on any relevant architectures is
not because it's not sufficient, it's because it hides problems.
libgcc has all these helpers for things that the kernel simply shouldn't do.
So _not_ linking against it is the thing that traditionally helps us
find problems, because you get things like
undefined symbol '__udivdi3'
or whatever.
In other words, avoiding libgcc is what protects us from people doing
(some) stupid things.
Linus
prev parent reply other threads:[~2021-09-14 19:53 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-13 20:32 [PATCH 5.10] overflow.h: use new generic division helpers to avoid / operator Nick Desaulniers
2021-09-13 21:05 ` Rasmus Villemoes
2021-09-14 0:23 ` [PATCH v2] " Nick Desaulniers
2021-09-14 17:22 ` Greg Kroah-Hartman
2021-09-14 18:07 ` Nick Desaulniers
2021-09-14 18:12 ` Greg Kroah-Hartman
2021-09-14 17:32 ` [PATCH 5.10] " Kees Cook
2021-09-14 18:14 ` Linus Torvalds
2021-09-14 18:30 ` Linus Torvalds
2021-09-14 18:44 ` Nick Desaulniers
2021-09-14 18:48 ` Linus Torvalds
2021-09-14 18:56 ` Linus Torvalds
2021-09-14 19:10 ` Nick Desaulniers
2021-09-14 19:45 ` Linus Torvalds
2021-09-14 19:50 ` Nick Desaulniers
2021-09-14 19:57 ` Linus Torvalds
2021-09-14 18:47 ` Kees Cook
2021-09-14 18:54 ` Linus Torvalds
2021-09-14 19:12 ` Nick Desaulniers
2021-09-14 19:52 ` Linus Torvalds [this message]
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