From: Kees Cook <keescook@chromium.org> To: Arnd Bergmann <arnd@arndb.de> Cc: linux-arch <linux-arch@vger.kernel.org>, linux-kbuild <linux-kbuild@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>, "linux-arm-kernel@lists.infradead.org" <linux-arm-kernel@lists.infradead.org>, Russell King <rmk+kernel@armlinux.org.uk>, Andrew Morton <akpm@linux-foundation.org>, kernel-build-reports@lists.linaro.org, kvmarm@lists.cs.columbia.edu Subject: Re: [RFC] minimum gcc version for kernel: raise to gcc-4.3 or 4.6? Date: Fri, 21 Apr 2017 14:05:35 -0700 [thread overview] Message-ID: <CAGXu5jJpofLF0qAf0-2iNTesZt-X704Q7L=DpQYdtHY5n2HD0w@mail.gmail.com> (raw) In-Reply-To: <CAK8P3a114EVbnhbObfq-4pZp8XCT4fWzMXD+WkRi7iPXs1vFMA@mail.gmail.com> On Fri, Apr 21, 2017 at 1:55 PM, Arnd Bergmann <arnd@arndb.de> wrote: > On Thu, Apr 20, 2017 at 9:52 PM, Kees Cook <keescook@chromium.org> wrote: >> On Thu, Apr 20, 2017 at 3:15 AM, Arnd Bergmann <arnd@arndb.de> wrote: >>> On Sun, Apr 16, 2017 at 9:52 PM, Kees Cook <keescook@chromium.org> wrote: >>>>>> The original gcc-4.3 release was in early 2008. If we decide to still >>>>>> support that, we probably want the first 10 quirks in this series, >>>>>> while gcc-4.6 (released in 2011) requires none of them. >>>> >>>> I'd be in support of raising the minimum to gcc 4.6. (I'd actually >>>> prefer 4.7, just to avoid some 4.6 packaging issues, and for better >>>> gcc plugin support.) >>>> >>>> I'm curious what gcc 4.6 binaries are common in the wild besides >>>> old-stable Debian (unsupported in maybe a year from now?) and 12.04 >>>> Ubuntu (going fully unsupported in 2 weeks). It looks like 4.6 was >>>> used only in Fedora 15 and 16 (both EOL). >>> >>> I think we are better off defining two versions: One that we know >>> a lot of people care about, and we actively try to make that work >>> well in all configurations (e.g. 4.6, 4.7 or 4.8), fixing all warnings >>> we run into, and an older version that we try not to break >>> intentionally (e.g. 3.4, 4.1 or 4.3) but that we only fix when >>> someone actually runs into a problem they can't work around >>> by upgrading to a more modern compiler. >> >> For "working well everywhere" I feel like 4.8 is the better of those >> three (I'd prefer 4.9). I think we should avoid 4.6 -- it seems not >> widely used. > > I suspect that 4.9 might be the one that actually works best > across architectures, and it contained some very significant > changes. In my testing gcc-5 tends to behave very similarly > to 4.9, and gcc-6 introduced a larger number of new warnings, > so that would clearly be too new for a recommended version. > > The suggestion of 4.9 or higher is appealing as a recommendation > because it matches what I would personally tell people: > > - If you have gcc-4.9 or newer and you don't rely on any newer > features, there is no need to upgrade > - Wth gcc-4.8, the -Wmaybe-uninitialized warnings are now turned > off because they were too noisy, so upgrading is probably a good > idea even though the compiler is otherwise ok and in widespread > use > - gcc-4.6 and 4.7 are basically usable for building kernels, but the > warning output is often counterproductive, and the generated > object code may be noticeably worse. > - anything before gcc-4.6 is missing too many features to be > useful on ARM, but may still be fine on other architectures. > > On the other hand, there is a noticeable difference in compile > speed, as a 5% slowdown compared to the previous release > apparently is not considered a regression. These are the times > I see for building ARM 'vexpress_defconfig': > > gcc-4.4: real 0m47.269s user 11m48.576s > gcc-4.5: real 0m44.878s user 10m58.900s > gcc-4.6: real 0m44.621s user 11m34.716s > gcc-4.7: real 0m47.476s user 12m42.924s > gcc-4.8: real 0m48.494s user 13m19.736s > gcc-4.9: real 0m50.140s user 13m44.876s > gcc-5.x: real 0m51.302s user 14m05.564s > gcc-6.x: real 0m54.615s user 15m06.304s > gcc-7.x: real 0m56.008s user 15m44.720s > > That is a factor of 1.5x in CPU cycles between slowest and > fastest, so there is clearly a benefit to keeping the old versions > around, but there is also no clear cut-off other thannoticing > that gcc-4.4 is slower than 4.5 in this particular > configuration. > >> For an old compiler... yikes. 3.4 sounds insane to me. :) > > That was my initial thought as well. On ARM, it clearly is > insane, as even gcc-4.0 is unable to build any of the modern > defconfigs (lacking -mabi=aapcs, ICE when building vsprintf.c) > and even the patch I did to get gcc-4.1 to build is probably > too ugly to get merged, so to build any unpatched kernel after > linux-3.6 you need at least gcc-4.2, or even gcc-4.4 for the > ''defconfig' (gcc-4.3 if you disable vdso). > > Then again, on x86, old cmpilers were claimed to be much better > supported. I just tried it out and found that no x86 defconfig kernel > since linux-3.2 could be built with gcc-3.4, probably not on any > other architecture either (it cannot have forward declarations > for inline functions and we have one in kernel/sched_fair.c). > > I think that would be a really good argument for requiring > something newer ;-) > > The linux-4.2 x86 defconfig could still be built with gcc-4.0, but > later kernels have several minor problems with that, and > require at least gcc-4.3. > > If we are ok with this status quo, we could simply declare gcc-4.3 > the absolute minimum version for the kernel, make gcc-4.9 > the recommeded minimum version, and remove all workarounds > for gcc-4.2 or older. I think starting with this would be a good first step. I'm not sure the best way to add "recommended minimum" to Documentation/process/changes.rst hmmm > If anyone has a good reason for gcc-4.0 through gcc-4.2, then > we would need a small number of patches to get them back > working with x86 defconfig. -Kees -- Kees Cook Pixel Security
WARNING: multiple messages have this Message-ID (diff)
From: keescook@chromium.org (Kees Cook) To: linux-arm-kernel@lists.infradead.org Subject: [RFC] minimum gcc version for kernel: raise to gcc-4.3 or 4.6? Date: Fri, 21 Apr 2017 14:05:35 -0700 [thread overview] Message-ID: <CAGXu5jJpofLF0qAf0-2iNTesZt-X704Q7L=DpQYdtHY5n2HD0w@mail.gmail.com> (raw) In-Reply-To: <CAK8P3a114EVbnhbObfq-4pZp8XCT4fWzMXD+WkRi7iPXs1vFMA@mail.gmail.com> On Fri, Apr 21, 2017 at 1:55 PM, Arnd Bergmann <arnd@arndb.de> wrote: > On Thu, Apr 20, 2017 at 9:52 PM, Kees Cook <keescook@chromium.org> wrote: >> On Thu, Apr 20, 2017 at 3:15 AM, Arnd Bergmann <arnd@arndb.de> wrote: >>> On Sun, Apr 16, 2017 at 9:52 PM, Kees Cook <keescook@chromium.org> wrote: >>>>>> The original gcc-4.3 release was in early 2008. If we decide to still >>>>>> support that, we probably want the first 10 quirks in this series, >>>>>> while gcc-4.6 (released in 2011) requires none of them. >>>> >>>> I'd be in support of raising the minimum to gcc 4.6. (I'd actually >>>> prefer 4.7, just to avoid some 4.6 packaging issues, and for better >>>> gcc plugin support.) >>>> >>>> I'm curious what gcc 4.6 binaries are common in the wild besides >>>> old-stable Debian (unsupported in maybe a year from now?) and 12.04 >>>> Ubuntu (going fully unsupported in 2 weeks). It looks like 4.6 was >>>> used only in Fedora 15 and 16 (both EOL). >>> >>> I think we are better off defining two versions: One that we know >>> a lot of people care about, and we actively try to make that work >>> well in all configurations (e.g. 4.6, 4.7 or 4.8), fixing all warnings >>> we run into, and an older version that we try not to break >>> intentionally (e.g. 3.4, 4.1 or 4.3) but that we only fix when >>> someone actually runs into a problem they can't work around >>> by upgrading to a more modern compiler. >> >> For "working well everywhere" I feel like 4.8 is the better of those >> three (I'd prefer 4.9). I think we should avoid 4.6 -- it seems not >> widely used. > > I suspect that 4.9 might be the one that actually works best > across architectures, and it contained some very significant > changes. In my testing gcc-5 tends to behave very similarly > to 4.9, and gcc-6 introduced a larger number of new warnings, > so that would clearly be too new for a recommended version. > > The suggestion of 4.9 or higher is appealing as a recommendation > because it matches what I would personally tell people: > > - If you have gcc-4.9 or newer and you don't rely on any newer > features, there is no need to upgrade > - Wth gcc-4.8, the -Wmaybe-uninitialized warnings are now turned > off because they were too noisy, so upgrading is probably a good > idea even though the compiler is otherwise ok and in widespread > use > - gcc-4.6 and 4.7 are basically usable for building kernels, but the > warning output is often counterproductive, and the generated > object code may be noticeably worse. > - anything before gcc-4.6 is missing too many features to be > useful on ARM, but may still be fine on other architectures. > > On the other hand, there is a noticeable difference in compile > speed, as a 5% slowdown compared to the previous release > apparently is not considered a regression. These are the times > I see for building ARM 'vexpress_defconfig': > > gcc-4.4: real 0m47.269s user 11m48.576s > gcc-4.5: real 0m44.878s user 10m58.900s > gcc-4.6: real 0m44.621s user 11m34.716s > gcc-4.7: real 0m47.476s user 12m42.924s > gcc-4.8: real 0m48.494s user 13m19.736s > gcc-4.9: real 0m50.140s user 13m44.876s > gcc-5.x: real 0m51.302s user 14m05.564s > gcc-6.x: real 0m54.615s user 15m06.304s > gcc-7.x: real 0m56.008s user 15m44.720s > > That is a factor of 1.5x in CPU cycles between slowest and > fastest, so there is clearly a benefit to keeping the old versions > around, but there is also no clear cut-off other thannoticing > that gcc-4.4 is slower than 4.5 in this particular > configuration. > >> For an old compiler... yikes. 3.4 sounds insane to me. :) > > That was my initial thought as well. On ARM, it clearly is > insane, as even gcc-4.0 is unable to build any of the modern > defconfigs (lacking -mabi=aapcs, ICE when building vsprintf.c) > and even the patch I did to get gcc-4.1 to build is probably > too ugly to get merged, so to build any unpatched kernel after > linux-3.6 you need at least gcc-4.2, or even gcc-4.4 for the > ''defconfig' (gcc-4.3 if you disable vdso). > > Then again, on x86, old cmpilers were claimed to be much better > supported. I just tried it out and found that no x86 defconfig kernel > since linux-3.2 could be built with gcc-3.4, probably not on any > other architecture either (it cannot have forward declarations > for inline functions and we have one in kernel/sched_fair.c). > > I think that would be a really good argument for requiring > something newer ;-) > > The linux-4.2 x86 defconfig could still be built with gcc-4.0, but > later kernels have several minor problems with that, and > require at least gcc-4.3. > > If we are ok with this status quo, we could simply declare gcc-4.3 > the absolute minimum version for the kernel, make gcc-4.9 > the recommeded minimum version, and remove all workarounds > for gcc-4.2 or older. I think starting with this would be a good first step. I'm not sure the best way to add "recommended minimum" to Documentation/process/changes.rst hmmm > If anyone has a good reason for gcc-4.0 through gcc-4.2, then > we would need a small number of patches to get them back > working with x86 defconfig. -Kees -- Kees Cook Pixel Security
next prev parent reply other threads:[~2017-04-21 21:05 UTC|newest] Thread overview: 113+ messages / expand[flat|nested] mbox.gz Atom feed top 2016-12-16 10:56 [RFC] minimum gcc version for kernel: raise to gcc-4.3 or 4.6? Arnd Bergmann 2016-12-16 10:56 ` Arnd Bergmann 2016-12-16 10:56 ` [PATCH 01/13] [HACK] gcc-4.5: avoid link errors for unused function pointers Arnd Bergmann 2016-12-16 10:56 ` Arnd Bergmann 2016-12-16 10:56 ` [PATCH 02/13] KVM: arm: fix gcc-4.5 build Arnd Bergmann 2016-12-16 10:56 ` Arnd Bergmann 2017-01-04 10:38 ` Christoffer Dall 2017-01-04 10:38 ` Christoffer Dall 2016-12-16 10:56 ` [PATCH 03/13] ARM: div64: fix building with gcc-4.5 and lower Arnd Bergmann 2016-12-16 10:56 ` Arnd Bergmann 2016-12-16 10:56 ` [PATCH 04/13] vfio-pci: use 32-bit comparisons for register address for gcc-4.5 Arnd Bergmann 2016-12-16 10:56 ` Arnd Bergmann 2016-12-16 15:30 ` Alex Williamson 2016-12-16 19:50 ` Arnd Bergmann 2016-12-16 10:56 ` [PATCH 05/13] clk: pxa: fix gcc-4.4 build Arnd Bergmann 2016-12-16 10:56 ` Arnd Bergmann 2016-12-16 10:56 ` [PATCH 06/13] ARM: atomic: " Arnd Bergmann 2016-12-16 10:56 ` Arnd Bergmann 2016-12-16 10:56 ` [PATCH 07/13] watchdog: kempld: fix gcc-4.3 build Arnd Bergmann 2016-12-16 10:56 ` Arnd Bergmann 2016-12-16 10:56 ` [PATCH 08/13] arm/arm64: xen: avoid gcc-4.4 warning Arnd Bergmann 2016-12-16 10:56 ` Arnd Bergmann 2016-12-16 10:56 ` [PATCH 09/13] ARM: mark cmpxchg and xchg __always_inline for gcc-4.3 Arnd Bergmann 2016-12-16 10:56 ` Arnd Bergmann 2016-12-16 10:56 ` [PATCH 10/13] asm-generic: mark cmpxchg as " Arnd Bergmann 2016-12-16 10:56 ` Arnd Bergmann 2016-12-16 10:56 ` [PATCH 11/13] fs: fix unsigned enum warning with gcc-4.2 Arnd Bergmann 2016-12-16 10:56 ` Arnd Bergmann 2017-01-03 22:47 ` Brendan Gregg 2017-02-28 21:53 ` Brendan Gregg 2016-12-16 10:56 ` [PATCH 12/13] KVM: arm: avoid binary number literals for gcc-4.2 Arnd Bergmann 2016-12-16 10:56 ` Arnd Bergmann 2017-01-04 10:39 ` Christoffer Dall 2017-01-04 10:39 ` Christoffer Dall 2016-12-16 10:56 ` [PATCH 13/13] ARM: avoid 'Q' asm constraint for gcc-4.1 and earlier Arnd Bergmann 2016-12-16 10:56 ` Arnd Bergmann 2016-12-16 11:14 ` [RFC] minimum gcc version for kernel: raise to gcc-4.3 or 4.6? Arnd Bergmann 2016-12-16 11:14 ` Arnd Bergmann 2016-12-16 11:14 ` Arnd Bergmann 2017-04-16 19:52 ` Kees Cook 2017-04-16 19:52 ` Kees Cook 2017-04-16 19:52 ` Kees Cook 2017-04-20 10:15 ` Arnd Bergmann 2017-04-20 10:15 ` Arnd Bergmann 2017-04-20 10:15 ` Arnd Bergmann 2017-04-20 19:52 ` Kees Cook 2017-04-20 19:52 ` Kees Cook 2017-04-20 19:52 ` Kees Cook 2017-04-20 19:52 ` Kees Cook 2017-04-21 20:55 ` Arnd Bergmann 2017-04-21 20:55 ` Arnd Bergmann 2017-04-21 20:55 ` Arnd Bergmann 2017-04-21 21:05 ` Kees Cook [this message] 2017-04-21 21:05 ` Kees Cook 2017-04-21 21:05 ` Kees Cook 2017-04-22 3:10 ` Maciej W. Rozycki 2017-04-22 3:10 ` Maciej W. Rozycki 2017-04-22 3:10 ` Maciej W. Rozycki 2017-04-22 15:30 ` Arnd Bergmann 2017-04-22 15:30 ` Arnd Bergmann 2017-04-22 15:30 ` Arnd Bergmann 2017-04-23 20:13 ` Geert Uytterhoeven 2017-04-23 20:13 ` Geert Uytterhoeven 2017-04-23 20:13 ` Geert Uytterhoeven 2017-04-23 20:13 ` Geert Uytterhoeven 2017-04-24 9:44 ` Arnd Bergmann 2017-04-24 9:44 ` Arnd Bergmann 2017-04-24 9:44 ` Arnd Bergmann 2017-04-24 9:44 ` Arnd Bergmann 2017-04-24 10:17 ` Geert Uytterhoeven 2017-04-24 10:17 ` Geert Uytterhoeven 2017-04-24 10:17 ` Geert Uytterhoeven 2017-04-24 10:17 ` Geert Uytterhoeven 2017-04-24 14:13 ` Arnd Bergmann 2017-04-24 14:13 ` Arnd Bergmann 2017-04-24 14:13 ` Arnd Bergmann 2017-04-24 16:53 ` Maciej W. Rozycki 2017-04-24 16:53 ` Maciej W. Rozycki 2017-04-24 16:53 ` Maciej W. Rozycki 2017-04-24 17:29 ` Arnd Bergmann 2017-04-24 17:29 ` Arnd Bergmann 2017-04-24 17:29 ` Arnd Bergmann 2017-04-24 18:16 ` Geert Uytterhoeven 2017-04-24 18:16 ` Geert Uytterhoeven 2017-04-24 18:16 ` Geert Uytterhoeven 2017-04-24 18:16 ` Geert Uytterhoeven 2017-04-24 18:30 ` Maciej W. Rozycki 2017-04-24 18:30 ` Maciej W. Rozycki 2017-04-24 18:30 ` Maciej W. Rozycki 2017-04-24 18:30 ` Maciej W. Rozycki 2017-04-24 20:30 ` Arnd Bergmann 2017-04-24 20:30 ` Arnd Bergmann 2017-04-24 20:30 ` Arnd Bergmann 2017-04-24 20:52 ` Kees Cook 2017-04-24 20:52 ` Kees Cook 2017-04-24 20:52 ` Kees Cook 2017-04-25 7:06 ` Geert Uytterhoeven 2017-04-25 7:06 ` Geert Uytterhoeven 2017-04-25 7:06 ` Geert Uytterhoeven 2017-04-25 9:22 ` Suzuki K Poulose 2017-04-25 9:22 ` Suzuki K Poulose 2017-04-25 9:22 ` Suzuki K Poulose 2016-12-16 15:54 ` Geert Uytterhoeven 2016-12-16 15:54 ` Geert Uytterhoeven 2016-12-16 19:58 ` Arnd Bergmann 2016-12-16 19:58 ` Arnd Bergmann 2016-12-16 20:34 ` Geert Uytterhoeven 2016-12-16 17:00 ` Sebastian Andrzej Siewior 2016-12-16 22:00 ` Arnd Bergmann 2016-12-16 22:00 ` Arnd Bergmann 2016-12-17 11:29 ` Sebastian Andrzej Siewior 2017-01-02 12:23 ` Russell King - ARM Linux 2016-12-20 9:59 ` Heiko Carstens
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='CAGXu5jJpofLF0qAf0-2iNTesZt-X704Q7L=DpQYdtHY5n2HD0w@mail.gmail.com' \ --to=keescook@chromium.org \ --cc=akpm@linux-foundation.org \ --cc=arnd@arndb.de \ --cc=kernel-build-reports@lists.linaro.org \ --cc=kvmarm@lists.cs.columbia.edu \ --cc=linux-arch@vger.kernel.org \ --cc=linux-arm-kernel@lists.infradead.org \ --cc=linux-kbuild@vger.kernel.org \ --cc=linux-kernel@vger.kernel.org \ --cc=rmk+kernel@armlinux.org.uk \ /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: linkBe sure your reply has a Subject: header at the top and a blank line before the message body.
This is an external index of several public inboxes, see mirroring instructions on how to clone and mirror all data and code used by this external index.