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kbuild: Create intermediate vmlinux build with relocations preserved

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The imperative paradigm used to build vmlinux, extract some info from it
or perform some checks on it, and subsequently modify it again goes
against the declarative paradigm that is usually employed for defining
make rules.

In particular, the Makefile.postlink files that consume their input via
an output rule result in some dodgy logic in the decompressor makefiles
for RISC-V and x86, given that the vmlinux.relocs input file needed to
generate the arch-specific relocation tables may not exist or be out of
date, but cannot be constructed using the ordinary Make dependency based
rules, because the info needs to be extracted while vmlinux is in its
ephemeral, non-stripped form.

So instead, for architectures that require the static relocations that
are emitted into vmlinux when passing --emit-relocs to the linker, and
are subsequently stripped out again, introduce an intermediate vmlinux
target called vmlinux.unstripped, and organize the reset of the build
logic accordingly:

- vmlinux.unstripped is created only once, and not updated again
- build rules under arch/*/boot can depend on vmlinux.unstripped without
  running the risk of the data disappearing or being out of date
- the final vmlinux generated by the build is not bloated with static
  relocations that are never needed again after the build completes.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
This commit is contained in:
Ard Biesheuvel
2025-03-11 12:06:20 +01:00
committed by Masahiro Yamada
parent 9b400d1725
commit ac4f06789b
9 changed files with 30 additions and 34 deletions
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28
scripts/Makefile.vmlinux
View File

@@ -9,6 +9,20 @@ include $(srctree)/scripts/Makefile.lib
targets :=
ifdef CONFIG_ARCH_VMLINUX_NEEDS_RELOCS
vmlinux-final := vmlinux.unstripped
quiet_cmd_strip_relocs = RSTRIP $@
cmd_strip_relocs = $(OBJCOPY) --remove-section='.rel*' $< $@
vmlinux: $(vmlinux-final) FORCE
$(call if_changed,strip_relocs)
targets += vmlinux
else
vmlinux-final := vmlinux
endif
%.o: %.c FORCE
$(call if_changed_rule,cc_o_c)
@@ -47,7 +61,7 @@ targets += .builtin-dtbs-list
ifdef CONFIG_GENERIC_BUILTIN_DTB
targets += .builtin-dtbs.S .builtin-dtbs.o
vmlinux: .builtin-dtbs.o
$(vmlinux-final): .builtin-dtbs.o
endif
# vmlinux
@@ -55,11 +69,11 @@ endif
ifdef CONFIG_MODULES
targets += .vmlinux.export.o
vmlinux: .vmlinux.export.o
$(vmlinux-final): .vmlinux.export.o
endif
ifdef CONFIG_ARCH_WANTS_PRE_LINK_VMLINUX
vmlinux: arch/$(SRCARCH)/tools/vmlinux.arch.o
$(vmlinux-final): arch/$(SRCARCH)/tools/vmlinux.arch.o
arch/$(SRCARCH)/tools/vmlinux.arch.o: vmlinux.o FORCE
$(Q)$(MAKE) $(build)=arch/$(SRCARCH)/tools $@
@@ -72,11 +86,11 @@ cmd_link_vmlinux = \
$< "$(LD)" "$(KBUILD_LDFLAGS)" "$(LDFLAGS_vmlinux)" "$@"; \
$(if $(ARCH_POSTLINK), $(MAKE) -f $(ARCH_POSTLINK) $@, true)
targets += vmlinux
vmlinux: scripts/link-vmlinux.sh vmlinux.o $(KBUILD_LDS) FORCE
targets += $(vmlinux-final)
$(vmlinux-final): scripts/link-vmlinux.sh vmlinux.o $(KBUILD_LDS) FORCE
+$(call if_changed_dep,link_vmlinux)
ifdef CONFIG_DEBUG_INFO_BTF
vmlinux: $(RESOLVE_BTFIDS)
$(vmlinux-final): $(RESOLVE_BTFIDS)
endif
ifdef CONFIG_BUILDTIME_TABLE_SORT
@@ -96,7 +110,7 @@ modules.builtin.ranges: $(srctree)/scripts/generate_builtin_ranges.awk \
modules.builtin vmlinux.map vmlinux.o.map FORCE
$(call if_changed,modules_builtin_ranges)
vmlinux.map: vmlinux
vmlinux.map: $(vmlinux-final)
@:
endif