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From: Linus Torvalds <torvalds@linux-foundation.org>
To: "Frank Ch. Eigler" <fche@redhat.com>
Cc: "Josh Boyer" <jwboyer@fedoraproject.org>,
	"Jakub Jelinek" <jakub@redhat.com>,
	"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
	"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
	stable <stable@vger.kernel.org>,
	"Michel Dänzer" <michel@daenzer.net>,
	"Markus Trippelsdorf" <markus@trippelsdorf.de>,
	"Josh Stone" <jistone@redhat.com>
Subject: Re: [PATCH 3.15 33/37] Fix gcc-4.9.0 miscompilation of load_balance() in scheduler
Date: Tue, 5 Aug 2014 15:36:39 -0700	[thread overview]
Message-ID: <CA+55aFwq72kDdRSWXKhyO1j=_PAKB960+RNOD6Cou0wZTa+5Hw@mail.gmail.com> (raw)
In-Reply-To: <20140805210728.GH13858@redhat.com>

On Tue, Aug 5, 2014 at 2:07 PM, Frank Ch. Eigler <fche@redhat.com> wrote:
>
> Actually, "perf probe" does (via HAVE_DWARF_SUPPORT), to place probes
> and to extract variables at those probes, much as systemtap does.
> Without var-tracking, probes placed at most interior points of
> functions will make variables inaccessible.

.. and as mentioned, -O2 already does that for many things, even
*with* tracking.

In other words, anybody who relies on it has already learnt to work
around it. Or, more likely, there just isn't anybody who relies on it.

I don't understand how you guys can be so cavalier about a compiler
bug that has already resulted in actual real problems. You bring up
theoretical cases that nobody has actually reported, and are
apparently ignoring the fact that the compiler generates INCORRECT
CODE. So on one hand we have known breakage, on the other we have
theoretical "I can make an example" arguments of behavior that no sane
user has ever done.

Do you compile without -O2 too? Because I *guarantee* you that with
-O2 (even with tracking), you'll get "local variable 'xyz' optimized
away" cases.

Christ.

I have asked the compiler people at least twice whether there is some
way to limit it to just gcc-4.9.0/1, but the compiler people didn't
step up and say that it was safe.

In the meantime, crazy people can choose to compile with known-broken
compilers. Until you can get the compiler people to have some sane way
to know the problem is gone, I'm not going to maintain a kernel that
uses a known-broken compiler feature. It's that simple.

              Linus

  reply	other threads:[~2014-08-05 22:36 UTC|newest]

Thread overview: 60+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-07-30  1:48 [PATCH 3.15 00/37] 3.15.8-stable review Greg Kroah-Hartman
2014-07-30  1:48 ` [PATCH 3.15 01/37] media: staging: tighten omap4iss dependencies Greg Kroah-Hartman
2014-07-30  1:48 ` [PATCH 3.15 02/37] media: media: v4l2-core: v4l2-dv-timings.c: Cleaning up code wrong value used in aspect ratio Greg Kroah-Hartman
2014-07-30  1:48 ` [PATCH 3.15 03/37] media: af9035: override tuner id when bad value set into eeprom Greg Kroah-Hartman
2014-07-30  1:48 ` [PATCH 3.15 04/37] media: hdpvr: fix two audio bugs Greg Kroah-Hartman
2014-07-30  1:48 ` [PATCH 3.15 05/37] media: tda10071: force modulation to QPSK on DVB-S Greg Kroah-Hartman
2014-07-30  1:48 ` [PATCH 3.15 06/37] nfs: only show Posix ACLs in listxattr if actually present Greg Kroah-Hartman
2014-07-30  1:48 ` [PATCH 3.15 07/37] xtensa: fix sysmem reservation at the end of existing block Greg Kroah-Hartman
2014-07-30  1:48 ` [PATCH 3.15 08/37] block: provide compat ioctl for BLKZEROOUT Greg Kroah-Hartman
2014-07-30  1:48 ` [PATCH 3.15 09/37] block: dont assume last put of shared tags is for the host Greg Kroah-Hartman
2014-07-30  1:48 ` [PATCH 3.15 10/37] libata: support the ata host which implements a queue depth less than 32 Greg Kroah-Hartman
2014-07-30  1:48 ` [PATCH 3.15 11/37] libata: introduce ata_host->n_tags to avoid oops on SAS controllers Greg Kroah-Hartman
2014-07-30  1:48 ` [PATCH 3.15 12/37] s390/ptrace: fix PSW mask check Greg Kroah-Hartman
2014-07-30  1:48 ` [PATCH 3.15 13/37] ahci: add support for the Promise FastTrak TX8660 SATA HBA (ahci mode) Greg Kroah-Hartman
2014-07-30  1:48 ` [PATCH 3.15 14/37] blkcg: dont call into policy draining if root_blkg is already gone Greg Kroah-Hartman
2014-07-30  1:48 ` [PATCH 3.15 15/37] tracing: Fix wraparound problems in "uptime" trace clock Greg Kroah-Hartman
2014-07-30  1:48 ` [PATCH 3.15 16/37] zram: avoid lockdep splat by revalidate_disk Greg Kroah-Hartman
2014-07-30  1:48 ` [PATCH 3.15 17/37] powerpc/pseries: dynamically added OF nodes need to call of_node_init Greg Kroah-Hartman
2014-07-30  1:48 ` [PATCH 3.15 18/37] slab_common: fix the check for duplicate slab names Greg Kroah-Hartman
2014-07-30  1:48 ` [PATCH 3.15 19/37] Input: synaptics - add min/max quirk for pnp-id LEN2002 (Edge E531) Greg Kroah-Hartman
2014-07-30  1:48 ` [PATCH 3.15 20/37] Input: fix defuzzing logic Greg Kroah-Hartman
2014-07-30  1:48 ` [PATCH 3.15 21/37] coredump: fix the setting of PF_DUMPCORE Greg Kroah-Hartman
2014-07-30  1:48 ` [PATCH 3.15 22/37] fuse: s_time_gran fix Greg Kroah-Hartman
2014-07-30  1:48 ` [PATCH 3.15 23/37] fuse: add FUSE_NO_OPEN_SUPPORT flag to INIT Greg Kroah-Hartman
2014-07-30  1:49 ` [PATCH 3.15 24/37] pinctrl: st: Fix irqmux handler Greg Kroah-Hartman
2014-07-30  1:49 ` [PATCH 3.15 25/37] parisc: Remove SA_RESTORER define Greg Kroah-Hartman
2014-07-30  1:49 ` [PATCH 3.15 26/37] hwmon: (smsc47m192) Fix temperature limit and vrm write operations Greg Kroah-Hartman
2014-07-30  1:49 ` [PATCH 3.15 27/37] parport: fix menu breakage Greg Kroah-Hartman
2014-07-30  1:49 ` [PATCH 3.15 28/37] fs: umount on symlink leaks mnt count Greg Kroah-Hartman
2014-07-30  1:49 ` [PATCH 3.15 29/37] x86_32, entry: Store badsys error code in %eax Greg Kroah-Hartman
2014-07-30  1:49 ` [PATCH 3.15 32/37] mm: hugetlb: fix copy_hugetlb_page_range() Greg Kroah-Hartman
2014-07-30  1:49 ` [PATCH 3.15 34/37] hwrng: virtio - ensure reads happen after successful probe Greg Kroah-Hartman
2014-07-30  1:49 ` [PATCH 3.15 35/37] mm: do not call do_fault_around for non-linear fault Greg Kroah-Hartman
2014-07-30  1:49 ` [PATCH 3.15 36/37] nl80211: move set_qos_map command into split state Greg Kroah-Hartman
2014-07-30  1:49 ` [PATCH 3.15 37/37] platform_get_irq: Revert to platform_get_resource if of_irq_get fails Greg Kroah-Hartman
     [not found] ` <20140730014829.344302554@linuxfoundation.org>
2014-07-30  6:53   ` [PATCH 3.15 33/37] Fix gcc-4.9.0 miscompilation of load_balance() in scheduler Jakub Jelinek
2014-07-30  7:13     ` Markus Trippelsdorf
2014-07-30  7:21       ` Jakub Jelinek
2014-07-30  7:27         ` Markus Trippelsdorf
2014-07-30 15:47     ` Linus Torvalds
2014-08-05 11:31       ` Josh Boyer
2014-08-05 11:46         ` Markus Trippelsdorf
2014-08-05 15:24           ` Jakub Jelinek
2014-08-05 15:19         ` Greg Kroah-Hartman
2014-08-05 16:49         ` Linus Torvalds
2014-08-05 20:57           ` Josh Boyer
2014-08-05 21:07             ` Frank Ch. Eigler
2014-08-05 22:36               ` Linus Torvalds [this message]
2014-08-05 23:30                 ` Frank Ch. Eigler
2014-08-05 23:59                   ` Linus Torvalds
2014-10-06 21:05                     ` [PATCH] Kbuild: Add an option to enable GCC VTA Josh Stone
2014-08-06  8:14                 ` [PATCH 3.15 33/37] Fix gcc-4.9.0 miscompilation of load_balance() in scheduler Jakub Jelinek
2014-08-06 10:23                   ` Måns Rullgård
2014-08-06 10:23                     ` Måns Rullgård
2014-08-06 16:34                   ` Alexei Starovoitov
2014-07-30 11:58 ` [PATCH 3.15 00/37] 3.15.8-stable review Satoru Takeuchi
2014-07-30 11:58   ` Satoru Takeuchi
2014-07-30 15:50   ` Greg Kroah-Hartman
2014-07-30 16:09 ` Guenter Roeck
2014-07-30 22:23   ` Greg Kroah-Hartman

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