FROMLIST: kbuild: fix dynamic ftrace with clang LTO

With CONFIG_LTO_CLANG enabled, LLVM IR won't be compiled into object
files until modpost_link. This change postpones calls to recordmcount
until after this step.

In order to exclude ftrace_process_locs from inspection, we add a new
code section .text..ftrace, which we tell recordmcount to ignore, and
a __norecordmcount attribute for moving functions to this section.

Bug: 62093296
Bug: 67506682
Bug: 133186739
Change-Id: Iba2c053968206acf533fadab1eb34a743b5088ee
(am from https://patchwork.kernel.org/patch/10060327/)
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>

scripts/Makefile.modpost

@@ -143,6 +143,10 @@ ifdef CONFIG_LTO_CLANG
 			echo -T $(@:.ko=.o.symversions))  		\
 		 -o $@ --whole-archive					\
 		 $(filter-out FORCE,$(^:$(modpost-ext).o=.o))
+
+  ifdef CONFIG_FTRACE_MCOUNT_RECORD
+      cmd_ld_ko_o += ; $(objtree)/scripts/recordmcount $(RECORDMCOUNT_FLAGS) $@
+  endif
 else
       cmd_ld_ko_o =                                                     \
 	$(LD) -r $(KBUILD_LDFLAGS)                                      \