BACKPORT: FROMGIT: kbuild: mkcompile_h: Include $LD version in /proc/version

When doing Clang builds of the kernel, it is possible to link with
either ld.bfd (binutils) or ld.lld (LLVM), but it is not possible to
discover this from a running kernel. Add the "$LD -v" output to
/proc/version.

Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
Tested-by: Nathan Chancellor <natechancellor@gmail.com>
Reviewed-by: Fangrui Song <maskray@google.com>
Reviewed-by: Sedat Dilek <sedat.dilek@gmail.com>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Bug: 153484457
(cherry picked from commit 6f04f056df3c
 https://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild.git
 for-next)
[nd: commit 4b950bb9ac0c ("Kbuild: Handle PREEMPT_RT for version string and magic")
     missing in 4.14, first landed in 5.4-rc1.
     commit b79c6aa6a1f1 ("kbuild: remove unnecessary in-subshell execution")
     missing in 4.14, first landed in 5.1-rc1.
]
Change-Id: Ifa5a98fe159392862e8d07a733c0f141fa9c7715
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>

init/Makefile

@@ -32,5 +32,6 @@ $(obj)/version.o: include/generated/compile.h
 silent_chk_compile.h = :
 include/generated/compile.h: FORCE
 	@$($(quiet)chk_compile.h)
-	$(Q)$(CONFIG_SHELL) $(srctree)/scripts/mkcompile_h $@ \
-	"$(UTS_MACHINE)" "$(CONFIG_SMP)" "$(CONFIG_PREEMPT)" "$(CC) $(KBUILD_CFLAGS)"
+	$(Q)$(CONFIG_SHELL) $(srctree)/scripts/mkcompile_h $@	\
+	"$(UTS_MACHINE)" "$(CONFIG_SMP)" "$(CONFIG_PREEMPT)"	\
+	"$(CC) $(KBUILD_CFLAGS)" "$(LD)"

scripts/mkcompile_h

@@ -6,6 +6,7 @@ ARCH=$2
 SMP=$3
 PREEMPT=$4
 CC=$5
+LD=$6
 
 vecho() { [ "${quiet}" = "silent_" ] || echo "$@" ; }
 
@@ -77,7 +78,10 @@ UTS_TRUNCATE="cut -b -$UTS_LEN"
   echo \#define LINUX_COMPILE_BY \"`echo $LINUX_COMPILE_BY | $UTS_TRUNCATE`\"
   echo \#define LINUX_COMPILE_HOST \"`echo $LINUX_COMPILE_HOST | $UTS_TRUNCATE`\"
 
-  echo \#define LINUX_COMPILER \"`$CC -v 2>&1 | grep ' version ' | sed 's/[[:space:]]*$//'`\"
+  CC_VERSION=$($CC -v 2>&1 | grep ' version ' | sed 's/[[:space:]]*$//')
+  LD_VERSION=$($LD -v | head -n1 | sed 's/(compatible with [^)]*)//' \
+		      | sed 's/[[:space:]]*$//')
+  printf '#define LINUX_COMPILER "%s"\n' "$CC_VERSION, $LD_VERSION"
 ) > .tmpcompile
 
 # Only replace the real compile.h if the new one is different,