linux-kernel - Re: [PATCH 00/10] raise minimum GCC version to 5.1

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Message-ID: <20210913094947.GB12225@amd>
Date:   Mon, 13 Sep 2021 11:49:48 +0200
From:   Pavel Machek <pavel@....cz>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Nathan Chancellor <nathan@...nel.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Joe Perches <joe@...ches.com>, Arnd Bergmann <arnd@...nel.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>, llvm@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 00/10] raise minimum GCC version to 5.1

Hi!

> commit fad7cd3310db ("nbd: add the check to prevent overflow in
> __nbd_ioctl()")
> 
> raised an issue from the fallback helpers added in
> 
> commit f0907827a8a9 ("compiler.h: enable builtin overflow checkers and add fallback code")
> 
> Specifically, the helpers for checking whether the results of a
> multiplication overflowed (__unsigned_mul_overflow,
> __signed_add_overflow) use the division operator when
> !COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW. This is problematic for 64b
> operands on 32b hosts.

Please don't. gcc 4.9.2 is still in use here.

Plus, someone will want to prevent overflow in -stable, too, and you
can't really raise gcc version there.

Best regards,
									Pavel
-- 
http://www.livejournal.com/~pavelmachek

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