diff options
| author | Nicolas Pitre <nicolas.pitre@linaro.org> | 2016-03-14 02:55:45 +0100 |
|---|---|---|
| committer | Russell King <rmk+kernel@arm.linux.org.uk> | 2016-04-07 21:57:02 +0100 |
| commit | 208fae5c3b9431013ad7bcea07cbcee114e7d163 (patch) | |
| tree | da2ce503a9f38d131a3157aa7ef3fdf5ab81b4a1 /arch | |
| parent | f2335a2a0a590c88e6cb68e4fb8cd835e81e827e (diff) | |
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>
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/arm/kernel/setup.c | 2 |
1 files changed, 2 insertions, 0 deletions
diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c index 139791ed473d..a28fce0bdbbe 100644 --- a/arch/arm/kernel/setup.c +++ b/arch/arm/kernel/setup.c @@ -430,11 +430,13 @@ static void __init patch_aeabi_idiv(void) pr_info("CPU: div instructions available: patching division code\n"); fn_addr = ((uintptr_t)&__aeabi_uidiv) & ~1; + asm ("" : "+g" (fn_addr)); ((u32 *)fn_addr)[0] = udiv_instruction(); ((u32 *)fn_addr)[1] = bx_lr_instruction(); flush_icache_range(fn_addr, fn_addr + 8); fn_addr = ((uintptr_t)&__aeabi_idiv) & ~1; + asm ("" : "+g" (fn_addr)); ((u32 *)fn_addr)[0] = sdiv_instruction(); ((u32 *)fn_addr)[1] = bx_lr_instruction(); flush_icache_range(fn_addr, fn_addr + 8); |