Patch "kbuild: fix linker feature test macros when cross compiling with Clang" has been added to the 4.14-stable tree

This is a note to let you know that I've just added the patch titled

kbuild: fix linker feature test macros when cross compiling with Clang

to the 4.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
kbuild-fix-linker-feature-test-macros-when-cross-compiling-with-clang.patch
and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Nick Desaulniers <[email protected]>
Date: Mon, 6 Nov 2017 10:47:54 -0800
Subject: kbuild: fix linker feature test macros when cross compiling with Clang

From: Nick Desaulniers <[email protected]>

commit 86a9df597cdd564d2d29c65897bcad42519e3678 upstream.

I was not seeing my linker flags getting added when using ld-option when cross compiling with Clang. Upon investigation, this seems to be due to a difference in how GCC vs Clang handle cross compilation.

GCC is configured at build time to support one backend, that is implicit when compiling. Clang is explicit via the use of -target <triple> and ships with all supported backends by default.

GNU Make feature test macros that compile then link will always fail when cross compiling with Clang unless Clang's triple is passed along to the compiler. For example:

$ clang -x c /dev/null -c -o temp.o
$ aarch64-linux-android/bin/ld -E temp.o
aarch64-linux-android/bin/ld:
unknown architecture of input file `temp.o' is incompatible with
aarch64 output
aarch64-linux-android/bin/ld:
warning: cannot find entry symbol _start; defaulting to
0000000000400078
$ echo $?
1

$ clang -target aarch64-linux-android- -x c /dev/null -c -o temp.o
$ aarch64-linux-android/bin/ld -E temp.o
aarch64-linux-android/bin/ld:
warning: cannot find entry symbol _start; defaulting to 00000000004002e4
$ echo $?
0

This causes conditional checks that invoke $(CC) without the target triple, then $(LD) on the result, to always fail.

---
 scripts/Kbuild.include |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

@@ -160,12 +160,13 @@ cc-if-fullversion = $(shell [ $(cc-fullv
 # cc-ldoption
 # Usage: ldflags += $(call cc-ldoption, -Wl$(comma)--hash-style=both)
 cc-ldoption = $(call try-run,\
-	$(CC) $(1) -nostdlib -x c /dev/null -o "$$TMP",$(1),$(2))
+	$(CC) $(1) $(KBUILD_CPPFLAGS) $(CC_OPTION_CFLAGS) -nostdlib -x c /dev/null -o "$$TMP",$(1),$(2))
 
 # ld-option
 # Usage: LDFLAGS += $(call ld-option, -X)
 ld-option = $(call try-run,\
-	$(CC) -x c /dev/null -c -o "$$TMPO" ; $(LD) $(1) "$$TMPO" -o "$$TMP",$(1),$(2))
+	$(CC) $(KBUILD_CPPFLAGS) $(CC_OPTION_CFLAGS) -x c /dev/null -c -o "$$TMPO"; \
+	$(LD) $(LDFLAGS) $(1) "$$TMPO" -o "$$TMP",$(1),$(2))
 
 # ar-option
 # Usage: KBUILD_ARFLAGS := $(call ar-option,D)

Patches currently in stable-queue which might be from [email protected] are

queue-4.14/kbuild-fix-linker-feature-test-macros-when-cross-compiling-with-clang.patch