[PATCH v2 3/3] kbuild: add generic support for built-in boot DTBs

Masahiro Yamada
2024-09-10T09:45:16Z

Some architectures embed boot DTBs in vmlinux. A potential issue for
these architectures is a race condition during parallel builds because
Kbuild descends into arch/*/boot/dts/ twice.

One build thread is initiated by the 'dtbs' target, which is a
prerequisite of the 'all' target in the top-level Makefile:

ifdef CONFIG_OF_EARLY_FLATTREE
all: dtbs
endif

For architectures that support the built-in boot dtb, arch/*/boot/dts/
is visited also during the ordinary directory traversal in order to
build obj-y objects that wrap DTBs.

Since these build threads are unaware of each other, they can run
simultaneously during parallel builds.

This commit introduces a generic build rule to scripts/Makefile.vmlinux
to support embedded boot DTBs in a race-free way. Architectures that
want to use this rule need to select CONFIG_GENERIC_BUILTIN_DTB.

After the migration, Makefiles under arch/*/boot/dts/ will be visited
only once to build only *.dtb files.

This change also aims to unify the CONFIG options used for built-in DTBs
support. Currently, different architectures use different CONFIG options
for the same purposes.

The CONFIG options are unified as follows:

- CONFIG_GENERIC_BUILTIN_DTB

This enables the generic rule for embedded boot DTBs. This will be
renamed to CONFIG_BUILTIN_DTB after all architectures migrate to the
generic rule.

- CONFIG_BUILTIN_DTB_NAME

This specifies the path to the embedded DTB.
(relative to arch/*/boot/dts/)

- CONFIG_BUILTIN_DTB_ALL

If this is enabled, all DTB files compiled under arch/*/boot/dts/ are
embedded into vmlinux. Only used by MIPS.

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

(no changes since v1)

Makefile | 7 ++++++-
drivers/of/Kconfig | 6 ++++++
scripts/Makefile.vmlinux | 44 ++++++++++++++++++++++++++++++++++++++++
scripts/link-vmlinux.sh | 4 ++++
4 files changed, 60 insertions(+), 1 deletion(-)

diff --git a/Makefile b/Makefile
index b4a941a30c73..efe8ac7d356c 100644
--- a/Makefile
+++ b/Makefile
@@ -1417,6 +1417,10 @@ ifdef CONFIG_OF_EARLY_FLATTREE
all: dtbs
endif

+ifdef CONFIG_GENERIC_BUILTIN_DTB
+vmlinux: dtbs
+endif
+
endif

PHONY += scripts_dtc
@@ -1484,7 +1488,8 @@ CLEAN_FILES += vmlinux.symvers modules-only.symvers \
modules.builtin modules.builtin.modinfo modules.nsdeps \
modules.builtin.ranges vmlinux.o.map \
compile_commands.json rust/test \
- rust-project.json .vmlinux.objs .vmlinux.export.c
+ rust-project.json .vmlinux.objs .vmlinux.export.c \
+ .builtin-dtbs-list .builtin-dtb.S

# Directories & files removed with 'make mrproper'
MRPROPER_FILES += include/config include/generated \
diff --git a/drivers/of/Kconfig b/drivers/of/Kconfig
index dd726c7056bf..5142e7d7fef8 100644
--- a/drivers/of/Kconfig
+++ b/drivers/of/Kconfig
@@ -2,6 +2,12 @@
config DTC
bool

+config GENERIC_BUILTIN_DTB
+ bool
+
+config BUILTIN_DTB_ALL
+ bool
+
menuconfig OF
bool "Device Tree and Open Firmware support"
help
diff --git a/scripts/Makefile.vmlinux b/scripts/Makefile.vmlinux
index dfb408aa19c6..50b341c3b8cf 100644
--- a/scripts/Makefile.vmlinux
+++ b/scripts/Makefile.vmlinux
@@ -17,6 +17,50 @@ quiet_cmd_cc_o_c = CC $@
%.o: %.c FORCE
$(call if_changed_dep,cc_o_c)

+quiet_cmd_as_o_S = AS $@
+ cmd_as_o_S = $(CC) $(a_flags) -c -o $@ $<
+
+%.o: %.S FORCE
+ $(call if_changed_dep,as_o_S)
+
+# Built-in dtb
+# ---------------------------------------------------------------------------
+
+quiet_cmd_wrap_dtbs = WRAP $@
+ cmd_wrap_dtbs = { \
+ echo '\#include <asm-generic/vmlinux.lds.h>'; \
+ echo '.section .dtb.init.rodata,"a"'; \
+ while read dtb; do \
+ symbase=__dtb_$$(basename -s .dtb "$${dtb}" | tr - _); \
+ echo '.balign STRUCT_ALIGNMENT'; \
+ echo ".global $${symbase}_begin"; \
+ echo "$${symbase}_begin:"; \
+ echo '.incbin "'$$dtb'" '; \
+ echo ".global $${symbase}_end"; \
+ echo "$${symbase}_end:"; \
+ done < $<; \
+ } > $@
+
+.builtin-dtbs.S: .builtin-dtbs-list FORCE
+ $(call if_changed,wrap_dtbs)
+
+quiet_cmd_gen_dtbs_list = GEN $@
+ cmd_gen_dtbs_list = \
+ $(if $(CONFIG_BUILTIN_DTB_NAME), echo "arch/$(SRCARCH)/boot/dts/$(CONFIG_BUILTIN_DTB_NAME).dtb",:) > $@
+
+.builtin-dtbs-list: arch/$(SRCARCH)/boot/dts/dtbs-list FORCE
+ $(call if_changed,$(if $(CONFIG_BUILTIN_DTB_ALL),copy,gen_dtbs_list))
+
+targets += .builtin-dtbs-list
+
+ifdef CONFIG_GENERIC_BUILTIN_DTB
+targets += .builtin-dtbs.S .builtin-dtbs.o
+vmlinux: .builtin-dtbs.o
+endif
+
+# vmlinux
+# ---------------------------------------------------------------------------
+
ifdef CONFIG_MODULES
targets += .vmlinux.export.o
vmlinux: .vmlinux.export.o
diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index c27b4e969f20..bd196944e350 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -68,6 +68,10 @@ vmlinux_link()
libs="${KBUILD_VMLINUX_LIBS}"
fi

+ if is_enabled CONFIG_GENERIC_BUILTIN_DTB; then
+ objs="${objs} .builtin-dtbs.o"
+ fi
+
if is_enabled CONFIG_MODULES; then
objs="${objs} .vmlinux.export.o"
fi
--
2.43.0