kbuild: introduce ccflags-remove-y and asflags-remove-y

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

The same applies to lib/livepatch/Makefile.

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.

The following are not affected because they have no sub-directories:

  arch/arm/boot/compressed/
  arch/powerpc/xmon/
  arch/sh/
  kernel/trace/

However, lib/ has several sub-directories.

To keep the behavior, I added ccflags-remove-y to all Makefiles
in subdirectories of lib/, except the following:

  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 2464a609de ("ftrace: do not trace library functions")
excluded too much. In the next commit, I will remove ccflags-remove-y
from the sub-directories of lib/.

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)
Tested-by: Anders Roxell <anders.roxell@linaro.org>

Documentation/kbuild/makefiles.rst

@@ -368,6 +368,14 @@ more details, with real examples.
 
 		subdir-ccflags-y := -Werror
 
+    ccflags-remove-y, asflags-remove-y
+	These flags are used to remove particular flags for the compiler,
+	assembler invocations.
+
+	Example::
+
+		ccflags-remove-$(CONFIG_MCOUNT) += -pg
+
     CFLAGS_$@, AFLAGS_$@
 	CFLAGS_$@ and AFLAGS_$@ only apply to commands in current
 	kbuild makefile.
@@ -375,6 +383,9 @@ more details, with real examples.
 	$(CFLAGS_$@) specifies per-file options for $(CC).  The $@
 	part has a literal value which specifies the file that it is for.
 
+	CFLAGS_$@ has the higher priority than ccflags-remove-y; CFLAGS_$@
+	can re-add compiler flags that were removed by ccflags-remove-y.
+
 	Example::
 
 		# drivers/scsi/Makefile
@@ -387,6 +398,9 @@ more details, with real examples.
 	$(AFLAGS_$@) is a similar feature for source files in assembly
 	languages.
 
+	AFLAGS_$@ has the higher priority than asflags-remove-y; AFLAGS_$@
+	can re-add assembler flags that were removed by asflags-remove-y.
+
 	Example::
 
 		# arch/arm/kernel/Makefile

arch/arm/boot/compressed/Makefile

@@ -102,13 +102,9 @@ clean-files += piggy_data lib1funcs.S ashldi3.S bswapsdi2.S hyp-stub.S
 
 KBUILD_CFLAGS += -DDISABLE_BRANCH_PROFILING
 
-ifeq ($(CONFIG_FUNCTION_TRACER),y)
-ORIG_CFLAGS := $(KBUILD_CFLAGS)
-KBUILD_CFLAGS = $(subst -pg, , $(ORIG_CFLAGS))
-endif
-
 ccflags-y := -fpic $(call cc-option,-mno-single-pic-base,) -fno-builtin \
 	     -I$(obj) $(DISABLE_ARM_SSP_PER_TASK_PLUGIN)
+ccflags-remove-$(CONFIG_FUNCTION_TRACER) += -pg
 asflags-y := -DZIMAGE
 
 # Supply kernel BSS size to the decompressor via a linker symbol.

arch/powerpc/xmon/Makefile

@@ -7,8 +7,7 @@ UBSAN_SANITIZE := n
 KASAN_SANITIZE := n
 
 # Disable ftrace for the entire directory
-ORIG_CFLAGS := $(KBUILD_CFLAGS)
+ccflags-remove-$(CONFIG_FUNCTION_TRACER) += $(CC_FLAGS_FTRACE)
-KBUILD_CFLAGS = $(subst $(CC_FLAGS_FTRACE),,$(ORIG_CFLAGS))
 
 ifdef CONFIG_CC_IS_CLANG
 # clang stores addresses on the stack causing the frame size to blow

arch/sh/boot/compressed/Makefile

@@ -28,10 +28,7 @@ IMAGE_OFFSET	:= $(shell /bin/bash -c 'printf "0x%08x" \
 			$(CONFIG_BOOT_LINK_OFFSET)]')
 endif
 
-ifeq ($(CONFIG_MCOUNT),y)
+ccflags-remove-$(CONFIG_MCOUNT) += -pg
-ORIG_CFLAGS := $(KBUILD_CFLAGS)
-KBUILD_CFLAGS = $(subst -pg, , $(ORIG_CFLAGS))
-endif
 
 LDFLAGS_vmlinux := --oformat $(ld-bfd) -Ttext $(IMAGE_OFFSET) -e startup \
 		   -T $(obj)/../../kernel/vmlinux.lds

kernel/trace/Makefile

@@ -2,9 +2,9 @@
 
 # Do not instrument the tracer itself:
 
+ccflags-remove-$(CONFIG_FUNCTION_TRACER) += $(CC_FLAGS_FTRACE)
+
 ifdef CONFIG_FUNCTION_TRACER
-ORIG_CFLAGS := $(KBUILD_CFLAGS)
-KBUILD_CFLAGS = $(subst $(CC_FLAGS_FTRACE),,$(ORIG_CFLAGS))
 
 # Avoid recursion due to instrumentation.
 KCSAN_SANITIZE := n

lib/842/Makefile

@@ -1,3 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0-only
+
+ccflags-remove-$(CONFIG_FUNCTION_TRACER) += $(CC_FLAGS_FTRACE)
+
 obj-$(CONFIG_842_COMPRESS) += 842_compress.o
 obj-$(CONFIG_842_DECOMPRESS) += 842_decompress.o

lib/Makefile

@@ -3,10 +3,7 @@
 # Makefile for some libs needed in the kernel.
 #
 
-ifdef CONFIG_FUNCTION_TRACER
+ccflags-remove-$(CONFIG_FUNCTION_TRACER) += $(CC_FLAGS_FTRACE)
-ORIG_CFLAGS := $(KBUILD_CFLAGS)
-KBUILD_CFLAGS = $(subst $(CC_FLAGS_FTRACE),,$(ORIG_CFLAGS))
-endif
 
 # These files are disabled because they produce lots of non-interesting and/or
 # flaky coverage that is not a function of syscall inputs. For example,

lib/crypto/Makefile

@@ -1,5 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0
 
+ccflags-remove-$(CONFIG_FUNCTION_TRACER) += $(CC_FLAGS_FTRACE)
+
 # chacha is used by the /dev/random driver which is always builtin
 obj-y						+= chacha.o
 obj-$(CONFIG_CRYPTO_LIB_CHACHA_GENERIC)		+= libchacha.o

lib/dim/Makefile

@@ -2,6 +2,8 @@
 # DIM Dynamic Interrupt Moderation library
 #
 
+ccflags-remove-$(CONFIG_FUNCTION_TRACER) += $(CC_FLAGS_FTRACE)
+
 obj-$(CONFIG_DIMLIB) += dim.o
 
 dim-y := dim.o net_dim.o rdma_dim.o

lib/fonts/Makefile

@@ -1,6 +1,8 @@
 # SPDX-License-Identifier: GPL-2.0
 # Font handling
 
+ccflags-remove-$(CONFIG_FUNCTION_TRACER) += $(CC_FLAGS_FTRACE)
+
 font-objs := fonts.o
 
 font-objs-$(CONFIG_FONT_SUN8x16)   += font_sun8x16.o

lib/kunit/Makefile

@@ -1,3 +1,6 @@
+
+ccflags-remove-$(CONFIG_FUNCTION_TRACER) += $(CC_FLAGS_FTRACE)
+
 obj-$(CONFIG_KUNIT) +=			kunit.o
 
 kunit-objs +=				test.o \

lib/livepatch/Makefile

@@ -2,6 +2,8 @@
 #
 # Makefile for livepatch test code.
 
+ccflags-remove-$(CONFIG_FUNCTION_TRACER) += $(CC_FLAGS_FTRACE)
+
 obj-$(CONFIG_TEST_LIVEPATCH) += test_klp_atomic_replace.o \
 				test_klp_callbacks_demo.o \
 				test_klp_callbacks_demo2.o \

lib/lz4/Makefile

@@ -1,5 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0-only
 ccflags-y += -O3
+ccflags-remove-$(CONFIG_FUNCTION_TRACER) += $(CC_FLAGS_FTRACE)
 
 obj-$(CONFIG_LZ4_COMPRESS) += lz4_compress.o
 obj-$(CONFIG_LZ4HC_COMPRESS) += lz4hc_compress.o

lib/lzo/Makefile

@@ -1,4 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0-only
+ccflags-remove-$(CONFIG_FUNCTION_TRACER) += $(CC_FLAGS_FTRACE)
+
 lzo_compress-objs := lzo1x_compress.o
 lzo_decompress-objs := lzo1x_decompress_safe.o
 

lib/math/Makefile

@@ -1,4 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0-only
+ccflags-remove-$(CONFIG_FUNCTION_TRACER) += $(CC_FLAGS_FTRACE)
+
 obj-y += div64.o gcd.o lcm.o int_pow.o int_sqrt.o reciprocal_div.o
 
 obj-$(CONFIG_CORDIC)		+= cordic.o

lib/mpi/Makefile

@@ -3,6 +3,8 @@
 # MPI multiprecision maths library (from gpg)
 #
 
+ccflags-remove-$(CONFIG_FUNCTION_TRACER) += $(CC_FLAGS_FTRACE)
+
 obj-$(CONFIG_MPILIB) = mpi.o
 
 mpi-y = \

lib/raid6/Makefile

@@ -1,4 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0
+
+ccflags-remove-$(CONFIG_FUNCTION_TRACER) += $(CC_FLAGS_FTRACE)
+
 obj-$(CONFIG_RAID6_PQ)	+= raid6_pq.o
 
 raid6_pq-y	+= algos.o recov.o tables.o int1.o int2.o int4.o \

lib/reed_solomon/Makefile

@@ -3,5 +3,7 @@
 # This is a modified version of reed solomon lib,
 #
 
+ccflags-remove-$(CONFIG_FUNCTION_TRACER) += $(CC_FLAGS_FTRACE)
+
 obj-$(CONFIG_REED_SOLOMON) += reed_solomon.o
 obj-$(CONFIG_REED_SOLOMON_TEST) += test_rslib.o

lib/xz/Makefile

@@ -1,4 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0-only
+
+ccflags-remove-$(CONFIG_FUNCTION_TRACER) += $(CC_FLAGS_FTRACE)
+
 obj-$(CONFIG_XZ_DEC) += xz_dec.o
 xz_dec-y := xz_dec_syms.o xz_dec_stream.o xz_dec_lzma2.o
 xz_dec-$(CONFIG_XZ_DEC_BCJ) += xz_dec_bcj.o

lib/zlib_deflate/Makefile

@@ -7,6 +7,8 @@
 # decompression code.
 #
 
+ccflags-remove-$(CONFIG_FUNCTION_TRACER) += $(CC_FLAGS_FTRACE)
+
 obj-$(CONFIG_ZLIB_DEFLATE) += zlib_deflate.o
 
 zlib_deflate-objs := deflate.o deftree.o deflate_syms.o

lib/zlib_dfltcc/Makefile

@@ -6,6 +6,8 @@
 # This is the code for s390 zlib hardware support.
 #
 
+ccflags-remove-$(CONFIG_FUNCTION_TRACER) += $(CC_FLAGS_FTRACE)
+
 obj-$(CONFIG_ZLIB_DFLTCC) += zlib_dfltcc.o
 
 zlib_dfltcc-objs := dfltcc.o dfltcc_deflate.o dfltcc_inflate.o dfltcc_syms.o

lib/zlib_inflate/Makefile

@@ -14,6 +14,8 @@
 # uncompression can be done without blocking on allocation).
 #
 
+ccflags-remove-$(CONFIG_FUNCTION_TRACER) += $(CC_FLAGS_FTRACE)
+
 obj-$(CONFIG_ZLIB_INFLATE) += zlib_inflate.o
 
 zlib_inflate-objs := inffast.o inflate.o infutil.o \

lib/zstd/Makefile

@@ -3,6 +3,7 @@ obj-$(CONFIG_ZSTD_COMPRESS) += zstd_compress.o
 obj-$(CONFIG_ZSTD_DECOMPRESS) += zstd_decompress.o
 
 ccflags-y += -O3
+ccflags-remove-$(CONFIG_FUNCTION_TRACER) += $(CC_FLAGS_FTRACE)
 
 zstd_compress-y := fse_compress.o huf_compress.o compress.o \
 		   entropy_common.o fse_decompress.o zstd_common.o

scripts/Makefile.lib

@@ -111,12 +111,14 @@ basename_flags = -DKBUILD_BASENAME=$(call name-fix,$(basetarget))
 modname_flags  = -DKBUILD_MODNAME=$(call name-fix,$(modname))
 modfile_flags  = -DKBUILD_MODFILE=$(call stringify,$(modfile))
 
-orig_c_flags   = $(KBUILD_CPPFLAGS) $(KBUILD_CFLAGS) \
+_c_flags       = $(filter-out $(CFLAGS_REMOVE_$(target-stem).o), \
-                 $(ccflags-y) $(CFLAGS_$(target-stem).o)
+                     $(filter-out $(ccflags-remove-y), \
-_c_flags       = $(filter-out $(CFLAGS_REMOVE_$(target-stem).o), $(orig_c_flags))
+                         $(KBUILD_CPPFLAGS) $(KBUILD_CFLAGS) $(ccflags-y)) \
-orig_a_flags   = $(KBUILD_CPPFLAGS) $(KBUILD_AFLAGS) \
+                     $(CFLAGS_$(target-stem).o))
-                 $(asflags-y) $(AFLAGS_$(target-stem).o)
+_a_flags       = $(filter-out $(AFLAGS_REMOVE_$(target-stem).o), \
-_a_flags       = $(filter-out $(AFLAGS_REMOVE_$(target-stem).o), $(orig_a_flags))
+                     $(filter-out $(asflags-remove-y), \
+                         $(KBUILD_CPPFLAGS) $(KBUILD_AFLAGS) $(asflags-y)) \
+                     $(AFLAGS_$(target-stem).o))
 _cpp_flags     = $(KBUILD_CPPFLAGS) $(cppflags-y) $(CPPFLAGS_$(target-stem).lds)
 
 #