On 2015/6/2 10:15, AKASHI Takahiro wrote: > On 05/30/2015 09:01 AM, Masami Hiramatsu wrote: >> On 2015/05/28 14:51, Li Bin wrote: >>> This patchset propose a method for gcc -mfentry feature(profile >>> before prologue) implementation for arm64, and propose the livepatch >>> implementation for arm64 based on this feature. >>> The gcc implementation about this feature will be post to the gcc >>> community soon. >>> >>> With this -mfentry feature, the entry of each function like: >>> >>> foo: >>> mov x9, x30 >>> bl __fentry__ >>> mov x30, x9 >>> [prologue] >>> ... >>> >>> The x9 is a callee corruptible register, and the __fentry__ function >>> is responsible to protect all registers, so it can be used to protect >>> the x30. And the added two instructions which is register mov operation >>> have ralatively small impact on performance. >> >> Hm, this implementation looks good to me :) >> This also enables us to KPROBES_ON_FTRACE too. > > Even if x9 is a callee-saved register, there is no way to restore its original > value in setting up a pt_regs in ftrace_reg_caller. Hi, Takahiro AKASHI Firstly, x9 is not a callee-saved but a caller-saved register(or being called corruptible register). Secondly, I think x9 is already protected properly, please reference the patch: [PATCH 1/5] livepatch: ftrace: arm64: Add support for DYNAMIC_FTRACE_WITH_REGS [PATCH 3/5] livepatch: ftrace: arm64: Add support for -mfentry on arm64 > It's not the right thing for KPROBES_ON_FTRACE, is it? > > Saving Link register in stack is not a big deal since the overhead of ftrace > is much bigger. Performance overhead is only one aspect of the problem, and more importantly, even worse is that it would break the arm64 ABI rules. Thanks, Li Bin > > -Takahiro AKASHI > > >> Thanks, >> >>> >>> This patchset has been tested on arm64 platform. >>> >>> Li Bin (4): >>> livepatch: ftrace: arm64: Add support for DYNAMIC_FTRACE_WITH_REGS >>> livepatch: ftrace: add ftrace_function_stub_ip function >>> livepatch: ftrace: arm64: Add support for -mfentry on arm64 >>> livepatch: arm64: add support for livepatch on arm64 >>> >>> Xie XiuQi (1): >>> livepatch: arm64: support relocation in a module >>> >>> arch/arm64/Kconfig | 5 + >>> arch/arm64/include/asm/ftrace.h | 9 + >>> arch/arm64/include/asm/livepatch.h | 45 +++++ >>> arch/arm64/kernel/Makefile | 1 + >>> arch/arm64/kernel/arm64ksyms.c | 4 + >>> arch/arm64/kernel/entry-ftrace.S | 154 +++++++++++++++- >>> arch/arm64/kernel/ftrace.c | 28 +++- >>> arch/arm64/kernel/livepatch.c | 41 ++++ >>> arch/arm64/kernel/module.c | 355 ++++++++++++++++++------------------ >>> include/linux/ftrace.h | 1 + >>> kernel/livepatch/core.c | 17 ++- >>> kernel/trace/ftrace.c | 32 ++++ >>> scripts/recordmcount.pl | 2 +- >>> 13 files changed, 508 insertions(+), 186 deletions(-) >>> create mode 100644 arch/arm64/include/asm/livepatch.h >>> create mode 100644 arch/arm64/kernel/livepatch.c >>> >>> -- >>> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in >>> the body of a message to majordomo@xxxxxxxxxxxxxxx >>> More majordomo info at http://vger.kernel.org/majordomo-info.html >>> Please read the FAQ at http://www.tux.org/lkml/ >>> >> >> > -- > 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 > > . > -- 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
