On Tue, Jul 7, 2020 at 2:22 AM Masahiro Yamada masahiroy@kernel.org wrote:
CFLAGS_REMOVE_<file>.o filters out flags when compiling a particular object, but there is no convenient way to do that for every object in a directory.
Add ccflags-remove-y and asflags-remove-y to make it easily.
Use ccflags-remove-y to clean up some Makefiles.
The add/remove order works as follows:
[1] KBUILD_CFLAGS specifies compiler flags used globally
[2] ccflags-y adds compiler flags for all objects in the current Makefile
[3] ccflags-remove-y removes compiler flags for all objects in the current Makefile (New feature)
[4] CFLAGS_<file> adds compiler flags per file.
[5] CFLAGS_REMOVE_<file> removes compiler flags per file.
Having [3] before [4] allows us to remove flags from most (but not all) objects in the current Makefile.
For example, kernel/trace/Makefile removes $(CC_FLAGS_FTRACE) from all objects in the directory, then adds it back to trace_selftest_dynamic.o and CFLAGS_trace_kprobe_selftest.o
Please note ccflags-remove-y has no effect to the sub-directories. In contrast, the previous notation got rid of compiler flags also from all the sub-directories.
arch/arm/boot/compressed/ arch/powerpc/xmon/ arch/sh/ kernel/trace/
... have no sub-directories.
lib/
... has several sub-directories.
To keep the behavior, I added ccflags-remove-y to all Makefiles in subdirectories of lib/, except:
lib/vdso/Makefile - Kbuild does not descend into this Makefile lib/raid/test/Makefile - This is not used for the kernel build
I think commit 2464a609ded0 ("ftrace: do not trace library functions") excluded too much. In later commit, I will try to remove ccflags-remove-y from sub-directory Makefiles.
Suggested-by: Sami Tolvanen samitolvanen@google.com Signed-off-by: Masahiro Yamada masahiroy@kernel.org Acked-by: Steven Rostedt (VMware) rostedt@goodmis.org Acked-by: Michael Ellerman mpe@ellerman.id.au (powerpc)
Acked-by: Brendan Higgins brendanhiggins@google.com (KUnit)