Revision - 208fae5 - ARM: 8550/1: protect idiv patching against undefined gcc behavior - origin: https://github.com/torvalds/linux

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05 April 2024, 19:05:47 UTC

Revision 208fae5c3b9431013ad7bcea07cbcee114e7d163 authored by Nicolas Pitre on 14 March 2016, 01:55:45 UTC, committed by Russell King on 07 April 2016, 20:57:02 UTC

ARM: 8550/1: protect idiv patching against undefined gcc behavior

It was reported that a kernel with CONFIG_ARM_PATCH_IDIV=y stopped
booting when compiled with the upcoming gcc 6.  Turns out that turning
a function address into a writable array is undefined and gcc 6 decided
it was OK to omit the store to the first word of the function while
still preserving the store to the second word.

Even though gcc 6 is now fixed to behave more coherently, it is a
mystery that gcc 4 and gcc 5 actually produce wanted code in the kernel.
And in fact the reduced test case to illustrate the issue does indeed
break with gcc < 6 as well.

In any case, let's guard the kernel against undefined compiler behavior
by hiding the nature of the array location as suggested by gcc
developers.

Reference: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70128

Signed-off-by: Nicolas Pitre <nico@linaro.org>
Reported-by: Marcin Juszkiewicz <mjuszkiewicz@redhat.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: stable@vger.kernel.org # v4.5
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 parent f2335a2

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Tip revision: 208fae5c3b9431013ad7bcea07cbcee114e7d163 authored by Nicolas Pitre on 14 March 2016, 01:55:45 UTC
ARM: 8550/1: protect idiv patching against undefined gcc behavior

Tip revision: 208fae5

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ARM: 8550/1: protect idiv patching against undefined gcc behavior

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