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Date:   Mon, 13 Sep 2021 11:49:48 +0200
From:   Pavel Machek <pavel@ucw.cz>
To:     Nick Desaulniers <ndesaulniers@google.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        Nathan Chancellor <nathan@kernel.org>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Joe Perches <joe@perches.com>, Arnd Bergmann <arnd@kernel.org>,
        Stephen Rothwell <sfr@canb.auug.org.au>, llvm@lists.linux.dev,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 00/10] raise minimum GCC version to 5.1
Message-ID: <20210913094947.GB12225@amd>
References: <20210910234047.1019925-1-ndesaulniers@google.com>
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Hi!

> commit fad7cd3310db ("nbd: add the check to prevent overflow in
> __nbd_ioctl()")
>=20
> raised an issue from the fallback helpers added in
>=20
> commit f0907827a8a9 ("compiler.h: enable builtin overflow checkers and ad=
d fallback code")
>=20
> 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
--=20
http://www.livejournal.com/~pavelmachek

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