On Mon, 13 Aug 2018 11:54:06 +0100
Julien Thierry [off-list ref] wrote:

quoted

--- a/arch/arm64/Makefile
+++ b/arch/arm64/Makefile

@@ -78,6 +78,15 @@ ifeq ($(CONFIG_ARM64_MODULE_PLTS),y)
  KBUILD_LDFLAGS_MODULE	+= -T $(srctree)/arch/arm64/kernel/module.lds
  endif
  
+ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
+  CC_FLAGS_FTRACE := -fpatchable-function-entry=2
+  KBUILD_CPPFLAGS += -DCC_USING_PATCHABLE_FUNCTION_ENTRY
+  ifeq ($(call cc-option,-fpatchable-function-entry=2),)
+    $(warning Cannot use CONFIG_DYNAMIC_FTRACE_WITH_REGS: \
+             -fpatchable-function-entry not supported by compiler)  

Shouldn't this be an error? The option -fpatchable-function-entry has 
been added to the CC_FLAGS_FTRACE, so any call to the compiler is gonna 
break anyway. Or am I missing something?

I'm guessing this adds a more informative message on that error. One
will know why -fpatchable-function-entry was added to the CFLAGS. I'm
for more informative error messages being a victim of poor error
messages causing me to dig deep into the guts of the build
infrastructure to figure out simple issues.

-- Steve