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kbuild: add generic support for built-in boot DTBs

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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.

With this commit, the CONFIG options will be unified as follows:

 - CONFIG_GENERIC_BUILTIN_DTB

   This enables the generic rule for built-in 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>
This commit is contained in:
Masahiro Yamada
2024-09-23 16:56:03 +09:00
parent 985d6cccb6
commit 654102df2a
4 changed files with 60 additions and 1 deletions
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44
scripts/Makefile.vmlinux
View File

@@ -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