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ARM: 6781/1: Thumb-2: Work around buggy Thumb-2 short branch relocations in gas

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Various binutils versions can resolve Thumb-2 branches to
locally-defined, preemptible global symbols as short-range "b.n"
branch instructions.

This is a problem, because there's no guarantee the final
destination of the symbol, or any candidate locations for a
trampoline, are within range of the branch.  For this reason, the
kernel does not support fixing up the R_ARM_THM_JUMP11 (102)
relocation in modules at all, and it makes little sense to add
support.

The symptom is that the kernel fails with an "unsupported
relocation" error when loading some modules.

Until fixed tools are available, passing
-fno-optimize-sibling-calls to gcc should prevent gcc generating
code which hits this problem, at the cost of a bit of extra runtime
stack usage in some cases.

The problem is described in more detail at:
    https://bugs.launchpad.net/binutils-linaro/+bug/725126

Only Thumb-2 kernels are affected.

This patch adds a new CONFIG_THUMB2_AVOID_R_ARM_THM_JUMP11 config
option which adds -fno-optimize-sibling-calls to CFLAGS_MODULE
when building a Thumb-2 kernel.

Signed-off-by: Dave Martin <dave.martin@linaro.org>
Acked-by: Nicolas Pitre <nicolas.pitre@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
This commit is contained in:
Dave Martin 2011-03-03 11:41:12 +01:00 committed by Russell King
parent 23bfdacf4e
commit 6f685c5cdd
2 changed files with 35 additions and 0 deletions
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31
arch/arm/Kconfig
View File

@ -1379,6 +1379,37 @@ config THUMB2_KERNEL
If unsure, say N.
config THUMB2_AVOID_R_ARM_THM_JUMP11
bool "Work around buggy Thumb-2 short branch relocations in gas"
depends on THUMB2_KERNEL && MODULES
default y
help
Various binutils versions can resolve Thumb-2 branches to
locally-defined, preemptible global symbols as short-range "b.n"
branch instructions.
This is a problem, because there's no guarantee the final
destination of the symbol, or any candidate locations for a
trampoline, are within range of the branch. For this reason, the
kernel does not support fixing up the R_ARM_THM_JUMP11 (102)
relocation in modules at all, and it makes little sense to add
support.
The symptom is that the kernel fails with an "unsupported
relocation" error when loading some modules.
Until fixed tools are available, passing
-fno-optimize-sibling-calls to gcc should prevent gcc generating
code which hits this problem, at the cost of a bit of extra runtime
stack usage in some cases.
The problem is described in more detail at:
https://bugs.launchpad.net/binutils-linaro/+bug/725126
Only Thumb-2 kernels are affected.
Unless you are sure your tools don't have this problem, say Y.
config ARM_ASM_UNIFIED
bool

4
arch/arm/Makefile
View File

@ -105,6 +105,10 @@ AFLAGS_AUTOIT :=$(call as-option,-Wa$(comma)-mimplicit-it=always,-Wa$(comma)-mau
AFLAGS_NOWARN :=$(call as-option,-Wa$(comma)-mno-warn-deprecated,-Wa$(comma)-W)
CFLAGS_THUMB2 :=-mthumb $(AFLAGS_AUTOIT) $(AFLAGS_NOWARN)
AFLAGS_THUMB2 :=$(CFLAGS_THUMB2) -Wa$(comma)-mthumb
# Work around buggy relocation from gas if requested:
ifeq ($(CONFIG_THUMB2_AVOID_R_ARM_THM_JUMP11),y)
CFLAGS_MODULE +=-fno-optimize-sibling-calls
endif
endif
# Need -Uarm for gcc < 3.x