On 2020-07-22, Masahiro Yamada wrote:
On Wed, Jul 22, 2020 at 2:31 AM 'Fangrui Song' via Clang Built Linux
<clang-built-linux@xxxxxxxxxxxxxxxx> wrote:
When CROSS_COMPILE is set (e.g. aarch64-linux-gnu-), if
$(CROSS_COMPILE)elfedit is found at /usr/bin/aarch64-linux-gnu-elfedit,
GCC_TOOLCHAIN_DIR will be set to /usr/bin/. --prefix= will be set to
/usr/bin/ and Clang as of 11 will search for both
$(prefix)aarch64-linux-gnu-$needle and $(prefix)$needle.
GCC searchs for $(prefix)aarch64-linux-gnu/$version/$needle,
$(prefix)aarch64-linux-gnu/$needle and $(prefix)$needle. In practice,
$(prefix)aarch64-linux-gnu/$needle rarely contains executables.
To better model how GCC's -B/--prefix takes in effect in practice, newer
Clang (since
https://github.com/llvm/llvm-project/commit/3452a0d8c17f7166f479706b293caf6ac76ffd90)
only searches for $(prefix)$needle. Currently it will find /usr/bin/as
instead of /usr/bin/aarch64-linux-gnu-as.
Set --prefix= to $(GCC_TOOLCHAIN_DIR)$(CROSS_COMPILE)
(/usr/bin/aarch64-linux-gnu-) so that newer Clang can find the
appropriate cross compiling GNU as (when -no-integrated-as is in
effect).
Cc: stable@xxxxxxxxxxxxxxx
Reported-by: Nathan Chancellor <natechancellor@xxxxxxxxx>
Signed-off-by: Fangrui Song <maskray@xxxxxxxxxx>
Reviewed-by: Nathan Chancellor <natechancellor@xxxxxxxxx>
Tested-by: Nathan Chancellor <natechancellor@xxxxxxxxx>
Tested-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Link: https://github.com/ClangBuiltLinux/linux/issues/1099
---
Changes in v2:
* Updated description to add tags and the llvm-project commit link.
* Fixed a typo.
Changes in v3:
* Add Cc: stable@xxxxxxxxxxxxxxx
---
Makefile | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/Makefile b/Makefile
index 0b5f8538bde5..3ac83e375b61 100644
--- a/Makefile
+++ b/Makefile
@@ -567,7 +567,7 @@ ifneq ($(shell $(CC) --version 2>&1 | head -n 1 | grep clang),)
ifneq ($(CROSS_COMPILE),)
CLANG_FLAGS += --target=$(notdir $(CROSS_COMPILE:%-=%))
GCC_TOOLCHAIN_DIR := $(dir $(shell which $(CROSS_COMPILE)elfedit))
-CLANG_FLAGS += --prefix=$(GCC_TOOLCHAIN_DIR)
+CLANG_FLAGS += --prefix=$(GCC_TOOLCHAIN_DIR)$(CROSS_COMPILE)
CROSS_COMPILE may contain the directory path
to the cross toolchains.
For example, I use aarch64-linux-gnu-*
installed in
/home/masahiro/tools/aarch64-linaro-7.5/bin
Basically, there are two ways to use it.
[1]
PATH=$PATH:/home/masahiro/tools/aarch64-linaro-7.5/bin
CROSS_COMPILE=aarch64-linux-gnu-
[2]
Without setting PATH,
CROSS_COMPILE=~/tools/aarch64-linaro-7.5/bin/aarch64-linux-gnu-
I usually do [2] (and so does intel's 0day bot).
This patch works for the use-case [1]
but if I do [2], --prefix is set to a strange path:
--prefix=/home/masahiro/tools/aarch64-linaro-7.5/bin//home/masahiro/tools/aarch64-linaro-7.5/bin/aarch64-linux-gnu-
Thanks. I did not know the use-case [2].
This explains why there is a `$(notdir ...)` in
`CLANG_FLAGS += --target=$(notdir $(CROSS_COMPILE:%-=%))`
Interestingly, the build is still successful.
Presumably Clang searches for more paths
when $(prefix)$needle is not found ?
The priority order is:
-B(--prefix), COMPILER_PATH, detected gcc-cross paths
(In GCC, -B paths get prepended to the COMPILER_PATH list. Clang<=11 incorrectly
adds -B to the COMPILER_PATH list. I have fixed it for 12.0.0)
If -B fails, the detected gcc-cross paths may still be able to find
/usr/bin/aarch64-linux-gnu-
For example, on my machine (a variant of Debian testing), Clang finds
$(realpath
/usr/lib/gcc-cross/aarch64-linux-gnu/9/../../../../aarch64-linux-gnu/bin/as),
which is /usr/bin/aarch64-linux-gnu-as
I applied your patch and added -v option
to see which assembler was internally invoked:
"/home/masahiro/tools/aarch64-linaro-7.5/lib/gcc/aarch64-linux-gnu/7.5.0/../../../../aarch64-linux-gnu/bin/as"
-EL -I ./arch/arm64/include -I ./arch/arm64/include/generated -I
./include -I ./arch/arm64/include/uapi -I
./arch/arm64/include/generated/uapi -I ./include/uapi -I
./include/generated/uapi -o kernel/smp.o /tmp/smp-2ec2c7.s
Ok, it looks like Clang found an alternative path
to the correct 'as'.
But, to keep the original behavior for both [1] and [2],
how about this?
CLANG_FLAGS += --prefix=$(GCC_TOOLCHAIN_DIR)$(notdir $(CROSS_COMPILE))
Then, I can get this:
"/home/masahiro/tools/aarch64-linaro-7.5/bin/aarch64-linux-gnu-as"
-EL -I ./arch/arm64/include -I ./arch/arm64/include/generated -I
./include -I ./arch/arm64/include/uapi -I
./arch/arm64/include/generated/uapi -I ./include/uapi -I
./include/generated/uapi -o kernel/smp.o /tmp/smp-16d76f.s
This looks good.
Agreed that `--prefix=$(GCC_TOOLCHAIN_DIR)$(notdir $(CROSS_COMPILE))` should work for both [1] and [2].
Shall I send a v4? Or you are kind enough that you'll just add your Signed-off-by: tag
and fix that for me? :)
GCC_TOOLCHAIN := $(realpath $(GCC_TOOLCHAIN_DIR)/..)
endif
ifneq ($(GCC_TOOLCHAIN),)
--
2.28.0.rc0.105.gf9edc3c819-goog
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--
Best Regards
Masahiro Yamada
