[RFC PATCH v4 11/17] kbuild: Add generic hook for architectures to use before the final vmlinux link

Naveen N Rao
2024-07-14T08:28:58Z

On powerpc, we would like to be able to make a pass on vmlinux.o and
generate a new object file to be linked into vmlinux. Add a generic pass
in Makefile.vmlinux that architectures can use for this purpose.

Architectures need to select CONFIG_ARCH_WANTS_PRE_LINK_VMLINUX and must
provide arch/<arch>/tools/Makefile with .arch.vmlinux.o target, which
will be invoked prior to the final vmlinux link step.

Signed-off-by: Naveen N Rao <naveen@kernel.org>
---
arch/Kconfig | 6 ++++++
scripts/Makefile.vmlinux | 8 ++++++++
scripts/link-vmlinux.sh | 11 ++++++++---
3 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/arch/Kconfig b/arch/Kconfig
index 975dd22a2dbd..ef868ff8156a 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -1643,4 +1643,10 @@ config CC_HAS_SANE_FUNCTION_ALIGNMENT
config ARCH_NEED_CMPXCHG_1_EMU
bool

+config ARCH_WANTS_PRE_LINK_VMLINUX
+ def_bool n
+ help
+ An architecture can select this if it provides arch/<arch>/tools/Makefile
+ with .arch.vmlinux.o target to be linked into vmlinux.
+
endmenu
diff --git a/scripts/Makefile.vmlinux b/scripts/Makefile.vmlinux
index 49946cb96844..6410e0be7f52 100644
--- a/scripts/Makefile.vmlinux
+++ b/scripts/Makefile.vmlinux
@@ -22,6 +22,14 @@ targets += .vmlinux.export.o
vmlinux: .vmlinux.export.o
endif

+ifdef CONFIG_ARCH_WANTS_PRE_LINK_VMLINUX
+targets += .arch.vmlinux.o
+.arch.vmlinux.o: vmlinux.o FORCE
+ $(Q)$(MAKE) $(build)=arch/$(SRCARCH)/tools .arch.vmlinux.o
+
+vmlinux: .arch.vmlinux.o
+endif
+
ARCH_POSTLINK := $(wildcard $(srctree)/arch/$(SRCARCH)/Makefile.postlink)

# Final link of vmlinux with optional arch pass after final link
diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index 518c70b8db50..aafaed1412ea 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -122,7 +122,7 @@ gen_btf()
return 1
fi

- vmlinux_link ${1}
+ vmlinux_link ${1} ${arch_vmlinux_o}

info "BTF" ${2}
LLVM_OBJCOPY="${OBJCOPY}" ${PAHOLE} -J ${PAHOLE_FLAGS} ${1}
@@ -178,7 +178,7 @@ kallsyms_step()
kallsymso=${kallsyms_vmlinux}.o
kallsyms_S=${kallsyms_vmlinux}.S

- vmlinux_link ${kallsyms_vmlinux} "${kallsymso_prev}" ${btf_vmlinux_bin_o}
+ vmlinux_link ${kallsyms_vmlinux} "${kallsymso_prev}" ${btf_vmlinux_bin_o} ${arch_vmlinux_o}
mksysmap ${kallsyms_vmlinux} ${kallsyms_vmlinux}.syms
kallsyms ${kallsyms_vmlinux}.syms ${kallsyms_S}

@@ -223,6 +223,11 @@ fi

${MAKE} -f "${srctree}/scripts/Makefile.build" obj=init init/version-timestamp.o

+arch_vmlinux_o=""
+if is_enabled CONFIG_ARCH_WANTS_PRE_LINK_VMLINUX; then
+ arch_vmlinux_o=.arch.vmlinux.o
+fi
+
btf_vmlinux_bin_o=""
if is_enabled CONFIG_DEBUG_INFO_BTF; then
btf_vmlinux_bin_o=.btf.vmlinux.bin.o
@@ -273,7 +278,7 @@ if is_enabled CONFIG_KALLSYMS; then
fi
fi

-vmlinux_link vmlinux "${kallsymso}" ${btf_vmlinux_bin_o}
+vmlinux_link vmlinux "${kallsymso}" ${btf_vmlinux_bin_o} ${arch_vmlinux_o}

# fill in BTF IDs
if is_enabled CONFIG_DEBUG_INFO_BTF && is_enabled CONFIG_BPF; then
--
2.45.2