Live patching, as we use it, deliberately disrupts the fabric of compile units; thus all assumptions a compiler can make about the control flow may be invalid. As an example, it could analyse that a callee does not touch a caller-saved register at all, so why waste memory bandwidth saving it? The register allocations for the live patch replacement function may however be quite different. Starting with this example, disable all compiler optimisations that do not strictly comply with the established calling conventions. Signed-off-by: Torsten Duwe <duwe@xxxxxxx> --- Working on the arm64 ftrace-with-regs/livepatch, it struck me that this is a general problem: with live patching, certain optimisations must be switched off for all architectures, the new(?) IPA register allocator in gcc6 is only one example. We should tackle this well before it bites us. Torsten --- Makefile | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/Makefile b/Makefile index b409076..424d2e6 100644 --- a/Makefile +++ b/Makefile @@ -743,6 +743,13 @@ KBUILD_CFLAGS += $(call cc-option, -femit-struct-debug-baseonly) \ $(call cc-option,-fno-var-tracking) endif +ifdef CONFIG_LIVEPATCH +# The compiler might generate ABI "shortcuts" to speed up the code, +# making assumptions which are no longer valid when live patching +# is enabled. Disable all of them. +KBUILD_CFLAGS += $(call cc-option,-fno-ipa-ra) +endif + ifdef CONFIG_FUNCTION_TRACER ifndef CC_FLAGS_FTRACE CC_FLAGS_FTRACE := -pg -- 2.6.6 -- To unsubscribe from this list: send the line "unsubscribe live-patching" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
