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Subject[PATCH 4.4 001/266] kbuild: simplify ld-option implementation
Date
From: Masahiro Yamada <yamada.masahiro@socionext.com>

commit 0294e6f4a0006856e1f36b8cd8fa088d9e499e98 upstream.

Currently, linker options are tested by the coordination of $(CC) and
$(LD) because $(LD) needs some object to link.

As commit 86a9df597cdd ("kbuild: fix linker feature test macros when
cross compiling with Clang") addressed, we need to make sure $(CC)
and $(LD) agree the underlying architecture of the passed object.

This could be a bit complex when we combine tools from different groups.
For example, we can use clang for $(CC), but we still need to rely on
GCC toolchain for $(LD).

So, I was searching for a way of standalone testing of linker options.
A trick I found is to use '-v'; this not only prints the version string,
but also tests if the given option is recognized.

If a given option is supported,

$ aarch64-linux-gnu-ld -v --fix-cortex-a53-843419
GNU ld (Linaro_Binutils-2017.11) 2.28.2.20170706
$ echo $?
0

If unsupported,

$ aarch64-linux-gnu-ld -v --fix-cortex-a53-843419
GNU ld (crosstool-NG linaro-1.13.1-4.7-2013.04-20130415 - Linaro GCC 2013.04) 2.23.1
aarch64-linux-gnu-ld: unrecognized option '--fix-cortex-a53-843419'
aarch64-linux-gnu-ld: use the --help option for usage information
$ echo $?
1

Gold works likewise.

$ aarch64-linux-gnu-ld.gold -v --fix-cortex-a53-843419
GNU gold (Linaro_Binutils-2017.11 2.28.2.20170706) 1.14
masahiro@pug:~/ref/linux$ echo $?
0
$ aarch64-linux-gnu-ld.gold -v --fix-cortex-a53-999999
GNU gold (Linaro_Binutils-2017.11 2.28.2.20170706) 1.14
aarch64-linux-gnu-ld.gold: --fix-cortex-a53-999999: unknown option
aarch64-linux-gnu-ld.gold: use the --help option for usage information
$ echo $?
1

LLD too.

$ ld.lld -v --gc-sections
LLD 7.0.0 (http://llvm.org/git/lld.git 4a0e4190e74cea19f8a8dc625ccaebdf8b5d1585) (compatible with GNU linkers)
$ echo $?
0
$ ld.lld -v --fix-cortex-a53-843419
LLD 7.0.0 (http://llvm.org/git/lld.git 4a0e4190e74cea19f8a8dc625ccaebdf8b5d1585) (compatible with GNU linkers)
$ echo $?
0
$ ld.lld -v --fix-cortex-a53-999999
ld.lld: error: unknown argument: --fix-cortex-a53-999999
LLD 7.0.0 (http://llvm.org/git/lld.git 4a0e4190e74cea19f8a8dc625ccaebdf8b5d1585) (compatible with GNU linkers)
$ echo $?
1

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
[nc: try-run-cached was added later, just use try-run, which is the
current mainline state]
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
scripts/Kbuild.include | 4 +---
1 file changed, 1 insertion(+), 3 deletions(-)

--- a/scripts/Kbuild.include
+++ b/scripts/Kbuild.include
@@ -156,9 +156,7 @@ cc-ldoption = $(call try-run,\

# ld-option
# Usage: LDFLAGS += $(call ld-option, -X)
-ld-option = $(call try-run,\
- $(CC) $(KBUILD_CPPFLAGS) $(KBUILD_CFLAGS) -x c /dev/null -c -o "$$TMPO"; \
- $(LD) $(LDFLAGS) $(1) "$$TMPO" -o "$$TMP",$(1),$(2))
+ld-option = $(call try-run, $(LD) $(LDFLAGS) $(1) -v,$(1),$(2))

# ar-option
# Usage: KBUILD_ARFLAGS := $(call ar-option,D)

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