[PATCH v2] kbuild: fix SIGPIPE error message for AR=gcc-ar and AR=llvm-ar

[Masahiro Yamada]

Jiri Slaby reported that building the kernel with AR=gcc-ar shows:
  /usr/bin/ar terminated with signal 13 [Broken pipe]

Nathan Chancellor reported the latest AR=llvm-ar shows
  error: write on a pipe with no reader

The latter occurs since LLVM commit 51b557adc131 ("Add an error message
to the default SIGPIPE handler").

The resulting vmlinux is correct, but it is better to silence it.

'head -n1' exits after reading the first line, so the pipe is closed.

Use 'sed -n 1p' to eat the stream till the end.

Fixes: 321648455061 ("kbuild: use obj-y instead extra-y for objects placed at the head")
Link: https://github.com/ClangBuiltLinux/linux/issues/1651
Reported-by: Jiri Slaby <jirislaby@xxxxxxxxxx>
Reported-by: Nathan Chancellor <nathan@xxxxxxxxxx>
Signed-off-by: Masahiro Yamada <masahiroy@xxxxxxxxxx>
Tested-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
---

Changes in v2:
  - Update commit description to mention llvm-ar

 Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Makefile b/Makefile
index e90bb2b38607..e9e7eff906a5 100644
--- a/Makefile
+++ b/Makefile
@@ -1218,7 +1218,7 @@ quiet_cmd_ar_vmlinux.a = AR      $@
       cmd_ar_vmlinux.a = \
 	rm -f $@; \
 	$(AR) cDPrST $@ $(KBUILD_VMLINUX_OBJS); \
-	$(AR) mPiT $$($(AR) t $@ | head -n1) $@ $$($(AR) t $@ | grep -F -f $(srctree)/scripts/head-object-list.txt)
+	$(AR) mPiT $$($(AR) t $@ | sed -n 1p) $@ $$($(AR) t $@ | grep -F -f $(srctree)/scripts/head-object-list.txt)
 
 targets += vmlinux.a
 vmlinux.a: $(KBUILD_VMLINUX_OBJS) scripts/head-object-list.txt autoksyms_recursive FORCE
-- 
2.34.1