kbuild: merge temporary vmlinux for BTF and kallsyms

CONFIG_DEBUG_INFO_BTF=y requires one additional link step.
(.tmp_vmlinux.btf)

CONFIG_KALLSYMS=y requires two additional link steps.
(.tmp_vmlinux.kallsyms1 and .tmp_vmlinux.kallsyms2)

Enabling both requires three additional link steps.

When CONFIG_DEBUG_INFO_BTF=y and CONFIG_KALLSYMS=y, the current build
process is as follows:

    KSYMS   .tmp_vmlinux.kallsyms0.S
    AS      .tmp_vmlinux.kallsyms0.o
    LD      .tmp_vmlinux.btf             # temporary vmlinux for BTF
    BTF     .btf.vmlinux.bin.o
    LD      .tmp_vmlinux.kallsyms1       # temporary vmlinux for kallsyms step 1
    NM      .tmp_vmlinux.kallsyms1.syms
    KSYMS   .tmp_vmlinux.kallsyms1.S
    AS      .tmp_vmlinux.kallsyms1.o
    LD      .tmp_vmlinux.kallsyms2       # temporary vmlinux for kallsyms step 2
    NM      .tmp_vmlinux.kallsyms2.syms
    KSYMS   .tmp_vmlinux.kallsyms2.S
    AS      .tmp_vmlinux.kallsyms2.o
    LD      vmlinux                      # final vmlinux

This is redundant because the BTF generation and the kallsyms step 1 can
be performed against the same temporary vmlinux.

When both CONFIG_DEBUG_INFO_BTF and CONFIG_KALLSYMS are enabled, we can
reduce the number of link steps by one.

This commit changes the build process as follows:

    KSYMS   .tmp_vmlinux0.kallsyms.S
    AS      .tmp_vmlinux0.kallsyms.o
    LD      .tmp_vmlinux1                # temporary vmlinux for BTF and kallsyms step 1
    BTF     .tmp_vmlinux1.btf.o
    NM      .tmp_vmlinux1.syms
    KSYMS   .tmp_vmlinux1.kallsyms.S
    AS      .tmp_vmlinux1.kallsyms.o
    LD      .tmp_vmlinux2                # temporary vmlinux for kallsyms step 2
    NM      .tmp_vmlinux2.syms
    KSYMS   .tmp_vmlinux2.kallsyms.S
    AS      .tmp_vmlinux2.kallsyms.o
    LD      vmlinux                      # final vmlinux

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>

diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index 83d605ba7241ad34251184b177513587b269f093..c64158a04f82d0018507c35bbcb6219a12ab5cf1 100755 (executable)
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -105,11 +105,10 @@ vmlinux_link()
 
 # generate .BTF typeinfo from DWARF debuginfo
 # ${1} - vmlinux image
-# ${2} - file to dump raw BTF data into
 gen_btf()
 {
        local pahole_ver
-       local btf_data=${2}
+       local btf_data=${1}.btf.o
 
        if ! [ -x "$(command -v ${PAHOLE})" ]; then
                echo >&2 "BTF: ${1}: pahole (${PAHOLE}) is not available"
@@ -122,8 +121,6 @@ gen_btf()
                return 1
        fi
 
-       vmlinux_link ${1}
-
        info BTF "${btf_data}"
        LLVM_OBJCOPY="${OBJCOPY}" ${PAHOLE} -J ${PAHOLE_FLAGS} ${1}
 
@@ -177,15 +174,13 @@ kallsyms()
        kallsymso=${2}.o
 }
 
-# Perform one step in kallsyms generation, including temporary linking of
-# vmlinux.
-kallsyms_step()
+# Perform kallsyms for the given temporary vmlinux.
+sysmap_and_kallsyms()
 {
-       kallsyms_vmlinux=.tmp_vmlinux.kallsyms${1}
+       mksysmap "${1}" "${1}.syms"
+       kallsyms "${1}.syms" "${1}.kallsyms"
 
-       vmlinux_link "${kallsyms_vmlinux}"
-       mksysmap "${kallsyms_vmlinux}" "${kallsyms_vmlinux}.syms"
-       kallsyms "${kallsyms_vmlinux}.syms" "${kallsyms_vmlinux}"
+       kallsyms_sysmap=${1}.syms
 }
 
 # Create map file with all symbols from ${1}
@@ -228,11 +223,21 @@ kallsymso=
 strip_debug=
 
 if is_enabled CONFIG_KALLSYMS; then
-       kallsyms /dev/null .tmp_vmlinux.kallsyms0
+       kallsyms /dev/null .tmp_vmlinux0.kallsyms
+fi
+
+if is_enabled CONFIG_KALLSYMS || is_enabled CONFIG_DEBUG_INFO_BTF; then
+
+       # The kallsyms linking does not need debug symbols, but the BTF does.
+       if ! is_enabled CONFIG_DEBUG_INFO_BTF; then
+               strip_debug=1
+       fi
+
+       vmlinux_link .tmp_vmlinux1
 fi
 
 if is_enabled CONFIG_DEBUG_INFO_BTF; then
-       if ! gen_btf .tmp_vmlinux.btf .btf.vmlinux.bin.o ; then
+       if ! gen_btf .tmp_vmlinux1; then
                echo >&2 "Failed to generate BTF for vmlinux"
                echo >&2 "Try to disable CONFIG_DEBUG_INFO_BTF"
                exit 1
@@ -268,14 +273,16 @@ if is_enabled CONFIG_KALLSYMS; then
        # The kallsyms linking does not need debug symbols included.
        strip_debug=1
 
-       kallsyms_step 1
+       sysmap_and_kallsyms .tmp_vmlinux1
        size1=$(${CONFIG_SHELL} "${srctree}/scripts/file-size.sh" ${kallsymso})
 
-       kallsyms_step 2
+       vmlinux_link .tmp_vmlinux2
+       sysmap_and_kallsyms .tmp_vmlinux2
        size2=$(${CONFIG_SHELL} "${srctree}/scripts/file-size.sh" ${kallsymso})
 
        if [ $size1 -ne $size2 ] || [ -n "${KALLSYMS_EXTRA_PASS}" ]; then
-               kallsyms_step 3
+               vmlinux_link .tmp_vmlinux3
+               sysmap_and_kallsyms .tmp_vmlinux3
        fi
 fi
 
@@ -301,7 +308,7 @@ fi
 
 # step a (see comment above)
 if is_enabled CONFIG_KALLSYMS; then
-       if ! cmp -s System.map ${kallsyms_vmlinux}.syms; then
+       if ! cmp -s System.map "${kallsyms_sysmap}"; then
                echo >&2 Inconsistent kallsyms data
                echo >&2 'Try "make KALLSYMS_EXTRA_PASS=1" as a workaround'
                exit 1