summaryrefslogtreecommitdiff
path: root/arch/arm
diff options
context:
space:
mode:
authorDave Martin <dave.martin@linaro.org>2011-03-03 11:41:12 +0100
committerRussell King <rmk+kernel@arm.linux.org.uk>2011-03-10 16:49:06 +0000
commit6f685c5cdd29649cf8cc8f57c72791159f936e07 (patch)
tree892575c8f378609771752e12e88d4f2699084c70 /arch/arm
parent23bfdacf4eb525ff3404161429cedaa281c23e47 (diff)
ARM: 6781/1: Thumb-2: Work around buggy Thumb-2 short branch relocations in gas
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>
Diffstat (limited to 'arch/arm')
-rw-r--r--arch/arm/Kconfig31
-rw-r--r--arch/arm/Makefile4
2 files changed, 35 insertions, 0 deletions
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 2fec7073f68..f871f2e1dd7 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -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
diff --git a/arch/arm/Makefile b/arch/arm/Makefile
index da525bc9614..6d611f407ce 100644
--- a/arch/arm/Makefile
+++ b/arch/arm/Makefile
@@ -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