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>

init/Makefile

@@ -35,4 +35,4 @@ include/generated/compile.h: FORCE
 	@$($(quiet)chk_compile.h)
 	$(Q)$(CONFIG_SHELL) $(srctree)/scripts/mkcompile_h $@	\
 	"$(UTS_MACHINE)" "$(CONFIG_SMP)" "$(CONFIG_PREEMPT)"	\
-	"$(CONFIG_PREEMPT_RT)" "$(CC) $(KBUILD_CFLAGS)"
+	"$(CONFIG_PREEMPT_RT)" "$(CC) $(KBUILD_CFLAGS)" "$(LD)"

scripts/mkcompile_h

@@ -7,6 +7,7 @@ SMP=$3
 PREEMPT=$4
 PREEMPT_RT=$5
 CC=$6
+LD=$7
 
 vecho() { [ "${quiet}" = "silent_" ] || echo "$@" ; }
 
@@ -61,7 +62,10 @@ UTS_VERSION="$(echo $UTS_VERSION $CONFIG_FLAGS $TIMESTAMP | cut -b -$UTS_LEN)"
   printf '#define LINUX_COMPILE_BY "%s"\n' "$LINUX_COMPILE_BY"
   echo \#define LINUX_COMPILE_HOST \"$LINUX_COMPILE_HOST\"
 
-  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,