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ARM: 8452/3: PJ4: make coprocessor access sequences buildable in Thumb2 mode

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The PJ4 inline asm sequence to write to cp15 cannot be built in Thumb-2
mode, due to the way it performs arithmetic on the program counter, so it
is built in ARM mode instead. However, building C files in ARM mode under
CONFIG_THUMB2_KERNEL is problematic, since the instrumentation performed
by subsystems like ftrace does not expect having to deal with interworking
branches.

Since the sequence in question is simply a poor man's ISB instruction,
let's use a straight 'isb' instead when building in Thumb2 mode. Thumb2
implies V7, so 'isb' should always be supported in that case.

Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
This commit is contained in:
Ard Biesheuvel 2015-12-22 08:24:59 +01:00 committed by Russell King
parent 36f46d6d5c
commit 5008efc83b
2 changed files with 4 additions and 1 deletions
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1
arch/arm/kernel/Makefile
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@ -73,7 +73,6 @@ obj-$(CONFIG_IWMMXT) += iwmmxt.o
obj-$(CONFIG_PERF_EVENTS) += perf_regs.o perf_callchain.o
obj-$(CONFIG_HW_PERF_EVENTS) += perf_event_xscale.o perf_event_v6.o \
perf_event_v7.o
CFLAGS_pj4-cp0.o := -marm
AFLAGS_iwmmxt.o := -Wa,-mcpu=iwmmxt
obj-$(CONFIG_ARM_CPU_TOPOLOGY) += topology.o
obj-$(CONFIG_VDSO) += vdso.o

4
arch/arm/kernel/pj4-cp0.c
View File

@ -66,9 +66,13 @@ static void __init pj4_cp_access_write(u32 value)
__asm__ __volatile__ (
"mcr p15, 0, %1, c1, c0, 2\n\t"
#ifdef CONFIG_THUMB2_KERNEL
"isb\n\t"
#else
"mrc p15, 0, %0, c1, c0, 2\n\t"
"mov %0, %0\n\t"
"sub pc, pc, #4\n\t"
#endif
: "=r" (temp) : "r" (value));
}