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From: Michael Ellerman <mpe@ellerman.id.au>
To: Kees Cook <keescook@chromium.org>,
	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
Date: Sat, 11 Sep 2021 20:42:49 +1000	[thread overview]
Message-ID: <8735qbmlzq.fsf@mpe.ellerman.id.au> (raw)
In-Reply-To: <202109101917.5BA95B87E0@keescook>

Kees Cook <keescook@chromium.org> writes:
> On Fri, Sep 10, 2021 at 04:40:37PM -0700, Nick Desaulniers wrote:
>> 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.
>> 
>> Also, because the macro is type agnostic, it is very difficult to write
>> a similarly type generic macro that dispatches to one of:
>> * div64_s64
>> * div64_u64
>> * div_s64
>> * div_u64
>
> Given that it's all compile-time type-aware goo, this isn't so bad. The
> gist[1] you linked off the bug report is pretty close. Needs some
> bikeshedding. ;)
>
>> Raising the minimum supported versions allows us to remove all of the
>> fallback helpers for !COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW, instead
>> dispatching the compiler builtins.
>> 
>> arm64 has already raised the minimum supported GCC version to 5.1, do
>> this for all targets now. See the link below for the previous
>> discussion.
>
> That said, I'd much prefer raising the minimum GCC -- no one appears
> to actually be building on 4.9 -- there are close to 200 errors (neé
> warnings) on x86_64 allmodconfig there currently.

I still do 4.9 builds on kisskb, but I agree there are a lot of
warnings, and no one ever has time to fix any.

cheers

  reply	other threads:[~2021-09-11 10:43 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-10 23:40 Nick Desaulniers
2021-09-10 23:40 ` [PATCH 01/10] Documentation: raise minimum supported version of GCC " Nick Desaulniers
2021-09-10 23:55   ` Nathan Chancellor
2021-09-11  0:16     ` Nick Desaulniers
2021-09-13 16:22   ` Kees Cook
2021-09-10 23:40 ` [PATCH 02/10] compiler.h: drop fallback overflow checkers Nick Desaulniers
2021-09-11  0:04   ` Nathan Chancellor
2021-09-14 15:33     ` Nick Desaulniers
2021-09-14 16:04       ` Nathan Chancellor
2021-09-13 16:21   ` Kees Cook
2021-09-10 23:40 ` [PATCH 03/10] mm/ksm: remove old GCC 4.9+ check Nick Desaulniers
2021-09-11  0:07   ` Nathan Chancellor
2021-09-13 16:22   ` Kees Cook
2021-09-10 23:40 ` [PATCH 04/10] Kconfig.debug: drop GCC 5+ version check for DWARF5 Nick Desaulniers
2021-09-11  0:08   ` Nathan Chancellor
2021-09-13 16:23   ` Kees Cook
2021-09-10 23:40 ` [PATCH 05/10] riscv: remove Kconfig check for GCC version for ARCH_RV64I Nick Desaulniers
2021-09-11  0:09   ` Nathan Chancellor
2021-09-13 16:23   ` Kees Cook
2021-10-05  0:40     ` Palmer Dabbelt
2021-10-05  0:50       ` Kees Cook
2021-10-05  0:57         ` Palmer Dabbelt
2021-09-10 23:40 ` [PATCH 06/10] powerpc: remove GCC version check for UPD_CONSTR Nick Desaulniers
2021-09-10 23:48   ` Nathan Chancellor
2021-09-11 10:43     ` Michael Ellerman
2021-09-11 15:34   ` Christophe Leroy
2021-09-10 23:40 ` [PATCH 07/10] arm64: remove GCC version check for ARCH_SUPPORTS_INT128 Nick Desaulniers
2021-09-11  0:10   ` Nathan Chancellor
2021-09-13 16:25   ` Kees Cook
2021-09-16 13:23   ` Catalin Marinas
2021-09-10 23:40 ` [PATCH 08/10] Makefile: drop GCC < 5 -fno-var-tracking-assignments workaround Nick Desaulniers
2021-09-11  0:11   ` Nathan Chancellor
2021-09-13 16:25   ` Kees Cook
2021-09-10 23:40 ` [PATCH 09/10] compiler-gcc.h: drop checks for older GCC versions Nick Desaulniers
2021-09-11  0:12   ` Nathan Chancellor
2021-09-13 16:26   ` Kees Cook
2021-09-10 23:40 ` [PATCH 10/10] vmlinux.lds.h: remove old check for GCC 4.9 Nick Desaulniers
2021-09-10 23:50   ` Nathan Chancellor
2021-09-14 15:21     ` Nick Desaulniers
2021-09-13 16:28   ` Kees Cook
2021-09-11  2:19 ` [PATCH 00/10] raise minimum GCC version to 5.1 Kees Cook
2021-09-11 10:42   ` Michael Ellerman [this message]
2021-09-13  9:49 ` Pavel Machek
2021-09-13 16:20   ` Kees Cook
2021-09-13 11:27 ` Arnd Bergmann

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