[PATCH v2 1/6] kbuild: add stamp file for vmlinux BTF data

[Thomas Weißschuh]

The upcoming module hashes functionality will build the modules in
between the generation of the BTF data and the final link of vmlinux.
Having a dependency from the modules on vmlinux would make this
impossible as it would mean having a cyclic dependency.
Break this cyclic dependency by introducing a new target.

Signed-off-by: Thomas Weißschuh <li...@weissschuh.net>
---
 scripts/Makefile.modfinal | 4 ++--
 scripts/link-vmlinux.sh   | 6 ++++++
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/scripts/Makefile.modfinal b/scripts/Makefile.modfinal
index 
542ba462ed3ec9607e0df10e26613a4c7ac318e8..5d01b553ec9a4565c8e5a6edd05665c409003bc1
 100644
--- a/scripts/Makefile.modfinal
+++ b/scripts/Makefile.modfinal
@@ -52,8 +52,8 @@ if_changed_except = $(if $(call 
newer_prereqs_except,$(2))$(cmd-check),      \
        printf '%s\n' 'savedcmd_$@ := $(make-cmd)' > $(dot-target).cmd, @:)
 
 # Re-generate module BTFs if either module's .ko or vmlinux changed
-%.ko: %.o %.mod.o .module-common.o $(objtree)/scripts/module.lds $(and 
$(CONFIG_DEBUG_INFO_BTF_MODULES),$(KBUILD_BUILTIN),$(objtree)/vmlinux) FORCE
-       +$(call if_changed_except,ld_ko_o,$(objtree)/vmlinux)
+%.ko: %.o %.mod.o .module-common.o $(objtree)/scripts/module.lds $(and 
$(CONFIG_DEBUG_INFO_BTF_MODULES),$(KBUILD_BUILTIN),$(objtree)/.tmp_vmlinux_btf.stamp)
 FORCE
+       +$(call if_changed_except,ld_ko_o,$(objtree)/.tmp_vmlinux_btf.stamp)
 ifdef CONFIG_DEBUG_INFO_BTF_MODULES
        +$(if $(newer-prereqs),$(call cmd,btf_ko))
 endif
diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index 
d853ddb3b28c1238ec9079ebbbe77df26980a0a1..803c8d6f35a7f29fb68b29afa8546f4dde0bd4cb
 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -112,6 +112,7 @@ vmlinux_link()
 gen_btf()
 {
        local btf_data=${1}.btf.o
+       local btf_stamp=.tmp_vmlinux_btf.stamp
 
        info BTF "${btf_data}"
        LLVM_OBJCOPY="${OBJCOPY}" ${PAHOLE} -J ${PAHOLE_FLAGS} ${1}
@@ -132,6 +133,11 @@ gen_btf()
        fi
        printf "${et_rel}" | dd of="${btf_data}" conv=notrunc bs=1 seek=16 
status=none
 
+       info STAMP $btf_stamp
+       if ! cmp --silent $btf_data $btf_stamp; then
+               cp $btf_data $btf_stamp
+       fi
+
        btf_vmlinux_bin_o=${btf_data}
 }
 

-- 
2.48.1