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| author | Masahiro Yamada <masahiroy@kernel.org> | 2020-07-07 11:21:16 +0200 |
|---|---|---|
| committer | Masahiro Yamada <masahiroy@kernel.org> | 2020-08-09 18:32:59 +0200 |
| commit | 15d5761ad31dfb194ebe76554e6af0437eb20424 (patch) | |
| tree | b2fdcab9a5bb39085f306ad089f17beeb00dd074 /Documentation/kbuild/makefiles.rst | |
| parent | kbuild: do not export LDFLAGS_vmlinux (diff) | |
| download | linux-15d5761ad31dfb194ebe76554e6af0437eb20424.tar.xz linux-15d5761ad31dfb194ebe76554e6af0437eb20424.zip | |
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 $(CC_FLAGS_FTRACE)
from all objects in the directory, then adds it back to
trace_selftest_dynamic.o and CFLAGS_trace_kprobe_selftest.o
The same applies to lib/livepatch/Makefile.
Please note ccflags-remove-y has no effect to the sub-directories.
In contrast, the previous notation got rid of compiler flags also from
all the sub-directories.
The following are not affected because they have no sub-directories:
arch/arm/boot/compressed/
arch/powerpc/xmon/
arch/sh/
kernel/trace/
However, lib/ has several sub-directories.
To keep the behavior, I added ccflags-remove-y to all Makefiles
in subdirectories of lib/, except the following:
lib/vdso/Makefile - Kbuild does not descend into this Makefile
lib/raid/test/Makefile - This is not used for the kernel build
I think commit 2464a609ded0 ("ftrace: do not trace library functions")
excluded too much. In the next commit, I will remove ccflags-remove-y
from the sub-directories of lib/.
Suggested-by: Sami Tolvanen <samitolvanen@google.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)
Acked-by: Brendan Higgins <brendanhiggins@google.com> (KUnit)
Tested-by: Anders Roxell <anders.roxell@linaro.org>
Diffstat (limited to 'Documentation/kbuild/makefiles.rst')
| -rw-r--r-- | Documentation/kbuild/makefiles.rst | 14 |
1 files changed, 14 insertions, 0 deletions
diff --git a/Documentation/kbuild/makefiles.rst b/Documentation/kbuild/makefiles.rst index 6515ebc12b6f..14d8e7d23c04 100644 --- a/Documentation/kbuild/makefiles.rst +++ b/Documentation/kbuild/makefiles.rst @@ -368,6 +368,14 @@ more details, with real examples. subdir-ccflags-y := -Werror + ccflags-remove-y, asflags-remove-y + These flags are used to remove particular flags for the compiler, + assembler invocations. + + Example:: + + ccflags-remove-$(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 |