Re: [PATCH v2 1/2] kbuild: introduce ccflags-remove-y and asflags-remove-y
On Tue, 7 Jul 2020 at 11:21, Masahiro Yamada wrote:
>
> CFLAGS_REMOVE_.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_ adds compiler flags per file.
>
> [5] CFLAGS_REMOVE_ 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
> Signed-off-by: Masahiro Yamada
> Acked-by: Steven Rostedt (VMware)
> Acked-by: Michael Ellerman (powerpc)
Tested-by: Anders Roxell
> ---
>
> 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
> ---
[PATCH v2 1/2] kbuild: introduce ccflags-remove-y and asflags-remove-y
CFLAGS_REMOVE_.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_ adds compiler flags per file.
[5] CFLAGS_REMOVE_ 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
Signed-off-by: Masahiro Yamada
Acked-by: Steven Rostedt (VMware)
Acked-by: Michael Ellerman (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
-
