[PATCH v8 5/5] arm64: use -fpatchable-function-entry if available

Torsten Duwe
2019-02-08T15:10:29Z

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@suse.de>

---
arch/arm64/Kconfig | 2 ++
arch/arm64/Makefile | 5 +++++
include/asm-generic/vmlinux.lds.h | 1 +
include/linux/compiler_types.h | 2 ++
kernel/module.c | 7 ++++++-
5 files changed, 16 insertions(+), 1 deletion(-)
--- 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
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -3122,7 +3122,12 @@ static int find_module_sections(struct m
#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_FENTRY
+ "__patchable_function_entries",
+#else
+ "__mcount_loc",
+#endif
sizeof(*mod->ftrace_callsites),
&mod->num_ftrace_callsites);
#endif