linux-kernel - [PATCH v7 3/3] arm64: use -fpatchable-function-entry if available

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Date:   Fri, 18 Jan 2019 17:39:13 +0100 (CET)
From:   duwe@....de (Torsten Duwe)
To:     Mark Rutland <mark.rutland@....com>,
        Will Deacon <will.deacon@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Julien Thierry <julien.thierry@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Arnd Bergmann <arnd@...db.de>,
        AKASHI Takahiro <takahiro.akashi@...aro.org>,
        Amit Daniel Kachhap <amit.kachhap@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        live-patching@...r.kernel.org
Subject: [PATCH v7 3/3] arm64: use -fpatchable-function-entry if available

Test whether gcc supports -fpatchable-function-entry and use it to promote
DYNAMIC_FTRACE to DYNAMIC_FTRACE_WITH_REGS. Amend support for the new object
section that holds the locations (__patchable_function_entries) and define
a proper "notrace" attribute to switch it off.

Signed-off-by: Torsten Duwe <duwe@...e.de>

---
 arch/arm64/Kconfig                |    2 ++
 arch/arm64/Makefile               |    5 +++++
 include/asm-generic/vmlinux.lds.h |    1 +
 include/linux/compiler_types.h    |    2 ++
 4 files changed, 10 insertions(+)
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -132,6 +132,8 @@ config ARM64
 	select HAVE_DEBUG_KMEMLEAK
 	select HAVE_DMA_CONTIGUOUS
 	select HAVE_DYNAMIC_FTRACE
+	select HAVE_DYNAMIC_FTRACE_WITH_REGS \
+		if $(cc-option,-fpatchable-function-entry=2)
 	select HAVE_EFFICIENT_UNALIGNED_ACCESS
 	select HAVE_FTRACE_MCOUNT_RECORD
 	select HAVE_FUNCTION_TRACER
--- a/arch/arm64/Makefile
+++ b/arch/arm64/Makefile
@@ -89,6 +89,11 @@ ifeq ($(CONFIG_ARM64_MODULE_PLTS),y)
 KBUILD_LDFLAGS_MODULE	+= -T $(srctree)/arch/arm64/kernel/module.lds
 endif
 
+ifeq ($(CONFIG_DYNAMIC_FTRACE_WITH_REGS),y)
+  KBUILD_CPPFLAGS += -DCC_USING_PATCHABLE_FENTRY
+  CC_FLAGS_FTRACE := -fpatchable-function-entry=2
+endif
+
 # Default value
 head-y		:= arch/arm64/kernel/head.o
 
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -113,6 +113,7 @@
 #define MCOUNT_REC()	. = ALIGN(8);				\
 			__start_mcount_loc = .;			\
 			KEEP(*(__mcount_loc))			\
+			KEEP(*(__patchable_function_entries))	\
 			__stop_mcount_loc = .;
 #else
 #define MCOUNT_REC()
--- a/include/linux/compiler_types.h
+++ b/include/linux/compiler_types.h
@@ -112,6 +112,8 @@ struct ftrace_likely_data {
 
 #if defined(CC_USING_HOTPATCH)
 #define notrace			__attribute__((hotpatch(0, 0)))
+#elif defined(CC_USING_PATCHABLE_FENTRY)
+#define notrace			__attribute__((patchable_function_entry(0)))
 #else
 #define notrace			__attribute__((__no_instrument_function__))
 #endif