Subject: [PATCH 3/3] arm64: use -fpatchable-function-entry if available

From: Jisheng Zhang <[email-masked]>
Date: Mon, 19 Aug 2019 11:29:02 +0000

From: Torsten Duwe <[email-masked]>

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 <[email-masked]>
---
 arch/arm64/Kconfig  | 2 ++
 arch/arm64/Makefile | 5 +++++
 kernel/module.c     | 7 ++++++-
 3 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 3adcec05b1f6..663392d1eae2 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -144,6 +144,8 @@ config ARM64
 	select HAVE_DEBUG_KMEMLEAK
 	select HAVE_DMA_CONTIGUOUS
 	select HAVE_DYNAMIC_FTRACE
+	select HAVE_DYNAMIC_FTRACE_WITH_REGS \
+		if $(cc-option,-fpatchable-function-entry=2)
 	select HAVE_EFFICIENT_UNALIGNED_ACCESS
 	select HAVE_FAST_GUP
 	select HAVE_FTRACE_MCOUNT_RECORD
diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
index 61de992bbea3..e827ad0298ab 100644
--- a/arch/arm64/Makefile
+++ b/arch/arm64/Makefile
@@ -104,6 +104,11 @@ ifeq ($(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_FUNCTION_ENTRY
+  CC_FLAGS_FTRACE := -fpatchable-function-entry=2
+endif
+
 # Default value
 head-y		:= arch/arm64/kernel/head.o
 
diff --git a/kernel/module.c b/kernel/module.c
index 5933395af9a0..0759f89adbd3 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -3136,7 +3136,12 @@ static int find_module_sections(struct module *mod, struct load_info *info)
 #endif
 #ifdef CONFIG_FTRACE_MCOUNT_RECORD
 	/* sechdrs[0].sh_size is always zero */
-	mod->ftrace_callsites = section_objs(info, "__mcount_loc",
+	mod->ftrace_callsites = section_objs(info,
+#ifdef CC_USING_PATCHABLE_FUNCTION_ENTRY
+					     "__patchable_function_entries",
+#else
+					     "__mcount_loc",
+#endif
 					     sizeof(*mod->ftrace_callsites),
 					     &mod->num_ftrace_callsites);
 #endif
-- 
2.23.0.rc1

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