linux-kernel - [PATCH v6 11/17] kbuild: Add generic hook for architectures to use before the final vmlinux link

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Message-ID: <20241018173632.277333-12-hbathini@linux.ibm.com>
Date: Fri, 18 Oct 2024 23:06:26 +0530
From: Hari Bathini <hbathini@...ux.ibm.com>
To: linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>, bpf@...r.kernel.org,
        linux-trace-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc: Michael Ellerman <mpe@...erman.id.au>, "Naveen N. Rao" <naveen@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Vishal Chourasia <vishalc@...ux.ibm.com>,
        Mahesh J Salgaonkar <mahesh@...ux.ibm.com>
Subject: [PATCH v6 11/17] kbuild: Add generic hook for architectures to use before the final vmlinux link

From: Naveen N Rao <naveen@...nel.org>

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@...nel.org>
Signed-off-by: Hari Bathini <hbathini@...ux.ibm.com>
---

Changes in v6:
* Intermediate files named vmlinux.arch.* instead of .vmlinux.arch.*
* Used 'bool' instead of 'def_bool n'
* Missing FORCE added for vmlinux.arch.o


 arch/Kconfig             | 6 ++++++
 scripts/Makefile.vmlinux | 7 +++++++
 scripts/link-vmlinux.sh  | 7 ++++++-
 3 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/arch/Kconfig b/arch/Kconfig
index 8af374ea1adc..a1538927c8c1 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -1684,4 +1684,10 @@ config CC_HAS_SANE_FUNCTION_ALIGNMENT
 config ARCH_NEED_CMPXCHG_1_EMU
 	bool
 
+config ARCH_WANTS_PRE_LINK_VMLINUX
+	bool
+	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 1284f05555b9..dddad554e912 100644
--- a/scripts/Makefile.vmlinux
+++ b/scripts/Makefile.vmlinux
@@ -22,6 +22,13 @@ targets += .vmlinux.export.o
 vmlinux: .vmlinux.export.o
 endif
 
+ifdef CONFIG_ARCH_WANTS_PRE_LINK_VMLINUX
+vmlinux: arch/$(SRCARCH)/tools/vmlinux.arch.o
+
+arch/$(SRCARCH)/tools/vmlinux.arch.o: vmlinux.o FORCE
+	$(Q)$(MAKE) $(build)=arch/$(SRCARCH)/tools $@
+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 a9b3f34a78d2..7acf4e31e51c 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -100,7 +100,7 @@ vmlinux_link()
 	${ld} ${ldflags} -o ${output}					\
 		${wl}--whole-archive ${objs} ${wl}--no-whole-archive	\
 		${wl}--start-group ${libs} ${wl}--end-group		\
-		${kallsymso} ${btf_vmlinux_bin_o} ${ldlibs}
+		${kallsymso} ${btf_vmlinux_bin_o} ${arch_vmlinux_o} ${ldlibs}
 }
 
 # generate .BTF typeinfo from DWARF debuginfo
@@ -198,6 +198,11 @@ 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/${SRCARCH}/tools/vmlinux.arch.o
+fi
+
 btf_vmlinux_bin_o=
 kallsymso=
 strip_debug=
-- 
2.47.0