arm64: switch to relative exception tables
Instead of using absolute addresses for both the exception location
and the fixup, use offsets relative to the exception table entry values.
Not only does this cut the size of the exception table in half, it is
also a prerequisite for KASLR, since absolute exception table entries
are subject to dynamic relocation, which is incompatible with the sorting
of the exception table that occurs at build time.
This patch also introduces the _ASM_EXTABLE preprocessor macro (which
exists on x86 as well) and its _asm_extable assembly counterpart, as
shorthands to emit exception table entries.
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h
index ba5aff6..70f7b9e 100644
--- a/arch/arm64/include/asm/assembler.h
+++ b/arch/arm64/include/asm/assembler.h
@@ -94,12 +94,19 @@
dmb \opt
.endm
+/*
+ * Emit an entry into the exception table
+ */
+ .macro _asm_extable, from, to
+ .pushsection __ex_table, "a"
+ .align 3
+ .long (\from - .), (\to - .)
+ .popsection
+ .endm
+
#define USER(l, x...) \
9999: x; \
- .section __ex_table,"a"; \
- .align 3; \
- .quad 9999b,l; \
- .previous
+ _asm_extable 9999b, l
/*
* Register aliases.