[PATCH v2 1/2] kbuild: introduce ccflags-remove-y and asflags-remove-y

From: Masahiro Yamada
Date: Tue Jul 07 2020 - 05:26:18 EST

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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@xxxxxxxxxx>
Signed-off-by: Masahiro Yamada <masahiroy@xxxxxxxxxx>
Acked-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
Acked-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx> (powerpc)
---

Changes in v2:
- Swap the order of [3] and [4] to keep the current behavior of
kernel/trace/Makefile.
- Add ccflags-remove-y to subdir Makefiles of lib/

Documentation/kbuild/makefiles.rst | 14 ++++++++++++++
arch/arm/boot/compressed/Makefile | 6 +-----
arch/powerpc/xmon/Makefile | 3 +--
arch/sh/boot/compressed/Makefile | 5 +----
kernel/trace/Makefile | 4 ++--
lib/842/Makefile | 3 +++
lib/Makefile | 5 +----
lib/crypto/Makefile | 2 ++
lib/dim/Makefile | 2 ++
lib/fonts/Makefile | 2 ++
lib/kunit/Makefile | 3 +++
lib/livepatch/Makefile | 2 ++
lib/lz4/Makefile | 1 +
lib/lzo/Makefile | 2 ++
lib/math/Makefile | 2 ++
lib/mpi/Makefile | 2 ++
lib/raid6/Makefile | 3 +++
lib/reed_solomon/Makefile | 2 ++
lib/xz/Makefile | 3 +++
lib/zlib_deflate/Makefile | 2 ++
lib/zlib_dfltcc/Makefile | 2 ++
lib/zlib_inflate/Makefile | 2 ++
lib/zstd/Makefile | 1 +
scripts/Makefile.lib | 14 ++++++++------
24 files changed, 64 insertions(+), 23 deletions(-)

diff --git a/Documentation/kbuild/makefiles.rst b/Documentation/kbuild/makefiles.rst
index 6515ebc12b6f..14d8e7d23c04 100644
--- a/Documentation/kbuild/makefiles.rst
+++ b/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
diff --git a/arch/arm/boot/compressed/Makefile b/arch/arm/boot/compressed/Makefile
index 00602a6fba04..3d5691b23951 100644
--- a/arch/arm/boot/compressed/Makefile
+++ b/arch/arm/boot/compressed/Makefile
@@ -103,13 +103,9 @@ 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.
diff --git a/arch/powerpc/xmon/Makefile b/arch/powerpc/xmon/Makefile
index 89c76ca35640..eb25d7554ffd 100644
--- a/arch/powerpc/xmon/Makefile
+++ b/arch/powerpc/xmon/Makefile
@@ -7,8 +7,7 @@ UBSAN_SANITIZE := n
KASAN_SANITIZE := n

# Disable ftrace for the entire directory
-ORIG_CFLAGS := $(KBUILD_CFLAGS)
-KBUILD_CFLAGS = $(subst $(CC_FLAGS_FTRACE),,$(ORIG_CFLAGS))
+ccflags-remove-$(CONFIG_FUNCTION_TRACER) += $(CC_FLAGS_FTRACE)

ifdef CONFIG_CC_IS_CLANG
# clang stores addresses on the stack causing the frame size to blow
diff --git a/arch/sh/boot/compressed/Makefile b/arch/sh/boot/compressed/Makefile
index ad0e2403e56f..589d2d8a573d 100644
--- a/arch/sh/boot/compressed/Makefile
+++ b/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)
-ORIG_CFLAGS := $(KBUILD_CFLAGS)
-KBUILD_CFLAGS = $(subst -pg, , $(ORIG_CFLAGS))
-endif
+ccflags-remove-$(CONFIG_MCOUNT) += -pg

LDFLAGS_vmlinux := --oformat $(ld-bfd) -Ttext $(IMAGE_OFFSET) -e startup \
-T $(obj)/../../kernel/vmlinux.lds
diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile
index 6575bb0a0434..7492844a8b1b 100644
--- a/kernel/trace/Makefile
+++ b/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
diff --git a/lib/842/Makefile b/lib/842/Makefile
index 6f7aad269288..b815e824ae37 100644
--- a/lib/842/Makefile
+++ b/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
diff --git a/lib/Makefile b/lib/Makefile
index b1c42c10073b..b2ed4beddd68 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -3,10 +3,7 @@
# Makefile for some libs needed in the kernel.
#

-ifdef CONFIG_FUNCTION_TRACER
-ORIG_CFLAGS := $(KBUILD_CFLAGS)
-KBUILD_CFLAGS = $(subst $(CC_FLAGS_FTRACE),,$(ORIG_CFLAGS))
-endif
+ccflags-remove-$(CONFIG_FUNCTION_TRACER) += $(CC_FLAGS_FTRACE)

# 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,
diff --git a/lib/crypto/Makefile b/lib/crypto/Makefile
index 3a435629d9ce..b557ef0b07c2 100644
--- a/lib/crypto/Makefile
+++ b/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
diff --git a/lib/dim/Makefile b/lib/dim/Makefile
index 1d6858a108cb..97fc3e89d34e 100644
--- a/lib/dim/Makefile
+++ b/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
diff --git a/lib/fonts/Makefile b/lib/fonts/Makefile
index ed95070860de..f951750c179e 100644
--- a/lib/fonts/Makefile
+++ b/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-$(CONFIG_FONT_SUN8x16) += font_sun8x16.o
diff --git a/lib/kunit/Makefile b/lib/kunit/Makefile
index 724b94311ca3..8c847557ab24 100644
--- a/lib/kunit/Makefile
+++ b/lib/kunit/Makefile
@@ -1,3 +1,6 @@
+
+ccflags-remove-$(CONFIG_FUNCTION_TRACER) += $(CC_FLAGS_FTRACE)
+
obj-$(CONFIG_KUNIT) += kunit.o

kunit-objs += test.o \
diff --git a/lib/livepatch/Makefile b/lib/livepatch/Makefile
index 295b94bff370..9abdf615b088 100644
--- a/lib/livepatch/Makefile
+++ b/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 \
diff --git a/lib/lz4/Makefile b/lib/lz4/Makefile
index 5b42242afaa2..53da4cab7015 100644
--- a/lib/lz4/Makefile
+++ b/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
diff --git a/lib/lzo/Makefile b/lib/lzo/Makefile
index 2f58fafbbddd..9565a555275b 100644
--- a/lib/lzo/Makefile
+++ b/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

diff --git a/lib/math/Makefile b/lib/math/Makefile
index be6909e943bd..49aa50e28185 100644
--- a/lib/math/Makefile
+++ b/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
diff --git a/lib/mpi/Makefile b/lib/mpi/Makefile
index d5874a7f5ff9..df7883521619 100644
--- a/lib/mpi/Makefile
+++ b/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 = \
diff --git a/lib/raid6/Makefile b/lib/raid6/Makefile
index b4c0df6d706d..3482d6ae3f3b 100644
--- a/lib/raid6/Makefile
+++ b/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 \
diff --git a/lib/reed_solomon/Makefile b/lib/reed_solomon/Makefile
index 5d4fa68f26cb..a5c9defdac7f 100644
--- a/lib/reed_solomon/Makefile
+++ b/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-$(CONFIG_REED_SOLOMON_TEST) += test_rslib.o
diff --git a/lib/xz/Makefile b/lib/xz/Makefile
index fa6af814a8d1..fae9b6c7c389 100644
--- a/lib/xz/Makefile
+++ b/lib/xz/Makefile
@@ -1,4 +1,7 @@
# SPDX-License-Identifier: GPL-2.0-only
+
+ccflags-remove-$(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
diff --git a/lib/zlib_deflate/Makefile b/lib/zlib_deflate/Makefile
index 2622e03c0b94..1fcefe73536f 100644
--- a/lib/zlib_deflate/Makefile
+++ b/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
diff --git a/lib/zlib_dfltcc/Makefile b/lib/zlib_dfltcc/Makefile
index 8e4d5afbbb10..7a8067f6e772 100644
--- a/lib/zlib_dfltcc/Makefile
+++ b/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
diff --git a/lib/zlib_inflate/Makefile b/lib/zlib_inflate/Makefile
index 27327d3e9f54..a451e96f9845 100644
--- a/lib/zlib_inflate/Makefile
+++ b/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 \
diff --git a/lib/zstd/Makefile b/lib/zstd/Makefile
index f5d778e7e5c7..01be908a2d94 100644
--- a/lib/zstd/Makefile
+++ b/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
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 916b2f7f7098..3629f66646d7 100644
--- a/scripts/Makefile.lib
+++ b/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) \
- $(ccflags-y) $(CFLAGS_$(target-stem).o)
-_c_flags = $(filter-out $(CFLAGS_REMOVE_$(target-stem).o), $(orig_c_flags))
-orig_a_flags = $(KBUILD_CPPFLAGS) $(KBUILD_AFLAGS) \
- $(asflags-y) $(AFLAGS_$(target-stem).o)
-_a_flags = $(filter-out $(AFLAGS_REMOVE_$(target-stem).o), $(orig_a_flags))
+_c_flags = $(filter-out $(CFLAGS_REMOVE_$(target-stem).o), \
+ $(filter-out $(ccflags-remove-y), \
+ $(KBUILD_CPPFLAGS) $(KBUILD_CFLAGS) $(ccflags-y)) \
+ $(CFLAGS_$(target-stem).o))
+_a_flags = $(filter-out $(AFLAGS_REMOVE_$(target-stem).o), \
+ $(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)

#
--
2.25.1

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