kbuild: split the build log of kallsyms

Currently, the build log shows KSYM + object name.

Precisely speaking, kallsyms generates a .S file and then the compiler
compiles it into a .o file. Split the build log into two.

[Before]

  GEN     modules.builtin
  LD      .tmp_vmlinux.kallsyms1
  KSYM    .tmp_vmlinux.kallsyms1.o
  LD      .tmp_vmlinux.kallsyms2
  KSYM    .tmp_vmlinux.kallsyms2.o
  LD      vmlinux

[After]

  GEN     modules.builtin
  LD      .tmp_vmlinux.kallsyms1
  KSYMS   .tmp_vmlinux.kallsyms1.S
  AS      .tmp_vmlinux.kallsyms1.o
  LD      .tmp_vmlinux.kallsyms2
  KSYMS   .tmp_vmlinux.kallsyms2.S
  AS      .tmp_vmlinux.kallsyms2.o
  LD      vmlinux

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

scripts/link-vmlinux.sh

@@ -169,10 +169,9 @@ gen_btf()
 	printf '\1' | dd of=${2} conv=notrunc bs=1 seek=16 status=none
 }
 
-# Create ${2} .o file with all symbols from the ${1} object file
+# Create ${2} .S file with all symbols from the ${1} object file
 kallsyms()
 {
-	info KSYM ${2}
 	local kallsymopt;
 
 	if [ -n "${CONFIG_KALLSYMS_ALL}" ]; then
@@ -187,13 +186,8 @@ kallsyms()
 		kallsymopt="${kallsymopt} --base-relative"
 	fi
 
-	local aflags="${KBUILD_AFLAGS} ${KBUILD_AFLAGS_KERNEL}               \
-		      ${NOSTDINC_FLAGS} ${LINUXINCLUDE} ${KBUILD_CPPFLAGS}"
-
-	local afile="`basename ${2} .o`.S"
-
-	${NM} -n ${1} | scripts/kallsyms ${kallsymopt} > ${afile}
-	${CC} ${aflags} -c -o ${2} ${afile}
+	info KSYMS ${2}
+	${NM} -n ${1} | scripts/kallsyms ${kallsymopt} > ${2}
 }
 
 # Perform one step in kallsyms generation, including temporary linking of
@@ -203,9 +197,15 @@ kallsyms_step()
 	kallsymso_prev=${kallsymso}
 	kallsyms_vmlinux=.tmp_vmlinux.kallsyms${1}
 	kallsymso=${kallsyms_vmlinux}.o
+	kallsyms_S=${kallsyms_vmlinux}.S
 
 	vmlinux_link ${kallsyms_vmlinux} "${kallsymso_prev}" ${btf_vmlinux_bin_o}
-	kallsyms ${kallsyms_vmlinux} ${kallsymso}
+	kallsyms ${kallsyms_vmlinux} ${kallsyms_S}
+
+	info AS ${kallsyms_S}
+	${CC} ${NOSTDINC_FLAGS} ${LINUXINCLUDE} ${KBUILD_CPPFLAGS} \
+	      ${KBUILD_AFLAGS} ${KBUILD_AFLAGS_KERNEL} \
+	      -c -o ${kallsymso} ${kallsyms_S}
 }
 
 # Create map file with all symbols from ${1}