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authorArd Biesheuvel <ard.biesheuvel@linaro.org>2016-02-25 20:48:53 +0100
committerCatalin Marinas <catalin.marinas@arm.com>2016-02-26 18:35:02 +0000
commit5be8b70af1ca78cefb8b756d157532360a5fd663 (patch)
treecf0e7c75c56791c07c5905286fec7fc95437b151 /arch/arm64/lib/Makefile
parentcc30e6b95c9a6d29f7d2083c9f64e8dec642a99e (diff)
downloadlinux-5be8b70af1ca78cefb8b756d157532360a5fd663.tar.bz2
arm64: lse: deal with clobbered IP registers after branch via PLT
The LSE atomics implementation uses runtime patching to patch in calls to out of line non-LSE atomics implementations on cores that lack hardware support for LSE. To avoid paying the overhead cost of a function call even if no call ends up being made, the bl instruction is kept invisible to the compiler, and the out of line implementations preserve all registers, not just the ones that they are required to preserve as per the AAPCS64. However, commit fd045f6cd98e ("arm64: add support for module PLTs") added support for routing branch instructions via veneers if the branch target offset exceeds the range of the ordinary relative branch instructions. Since this deals with jump and call instructions that are exposed to ELF relocations, the PLT code uses x16 to hold the address of the branch target when it performs an indirect branch-to-register, something which is explicitly allowed by the AAPCS64 (and ordinary compiler generated code does not expect register x16 or x17 to retain their values across a bl instruction). Since the lse runtime patched bl instructions don't adhere to the AAPCS64, they don't deal with this clobbering of registers x16 and x17. So add them to the clobber list of the asm() statements that perform the call instructions, and drop x16 and x17 from the list of registers that are callee saved in the out of line non-LSE implementations. In addition, since we have given these functions two scratch registers, they no longer need to stack/unstack temp registers. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> [will: factored clobber list into #define, updated Makefile comment] Signed-off-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Diffstat (limited to 'arch/arm64/lib/Makefile')
-rw-r--r--arch/arm64/lib/Makefile13
1 files changed, 7 insertions, 6 deletions
diff --git a/arch/arm64/lib/Makefile b/arch/arm64/lib/Makefile
index 1a811ecf71da..c86b7909ef31 100644
--- a/arch/arm64/lib/Makefile
+++ b/arch/arm64/lib/Makefile
@@ -4,15 +4,16 @@ lib-y := bitops.o clear_user.o delay.o copy_from_user.o \
memcmp.o strcmp.o strncmp.o strlen.o strnlen.o \
strchr.o strrchr.o
-# Tell the compiler to treat all general purpose registers as
-# callee-saved, which allows for efficient runtime patching of the bl
-# instruction in the caller with an atomic instruction when supported by
-# the CPU. Result and argument registers are handled correctly, based on
-# the function prototype.
+# Tell the compiler to treat all general purpose registers (with the
+# exception of the IP registers, which are already handled by the caller
+# in case of a PLT) as callee-saved, which allows for efficient runtime
+# patching of the bl instruction in the caller with an atomic instruction
+# when supported by the CPU. Result and argument registers are handled
+# correctly, based on the function prototype.
lib-$(CONFIG_ARM64_LSE_ATOMICS) += atomic_ll_sc.o
CFLAGS_atomic_ll_sc.o := -fcall-used-x0 -ffixed-x1 -ffixed-x2 \
-ffixed-x3 -ffixed-x4 -ffixed-x5 -ffixed-x6 \
-ffixed-x7 -fcall-saved-x8 -fcall-saved-x9 \
-fcall-saved-x10 -fcall-saved-x11 -fcall-saved-x12 \
-fcall-saved-x13 -fcall-saved-x14 -fcall-saved-x15 \
- -fcall-saved-x16 -fcall-saved-x17 -fcall-saved-x18
+ -fcall-saved-x18