On Wed, Jun 3, 2020 at 3:45 PM Ard Biesheuvel <ardb@xxxxxxxxxx> wrote:
>
> On Wed, 3 Jun 2020 at 07:34, Masahiro Yamada <masahiroy@xxxxxxxxxx> wrote:
> >
> > Documentation/kbuild/makefiles.rst says:
> >
> > Use of lib-y is normally restricted to `lib/` and `arch/*/lib`.
> >
> > I want to disallow lib-y outside of them.
> >
>
> Why?
Because I plan to remove lib-y entirely at some point.
lib-y is not so useful to shrink the image size because:
- An object in lib.a can be omitted only when no symbol
in that object is referenced. This rarely happens.
- lib-y objects are often exported by nature
because lib-y is a collection of utility functions.
Even if no in-tree user, we always need to keep them
because EXPORT_SYMBOL() is the interface to modules.
When I worked on commit 7273ad2b08f8ac9563579d16a3cf528857b26f49,
I made some research.
The benefit of lib-y is just 362 byte for x86_64_defconfig.
( Before: 26578002, After: 26578364)
My hope is lib-y will be replaced by dead-code elimination or
ultimately by LTO.
drivers/firmware/efi/libstub/Makefile
is the only Makefile that breaks the rule:
"Use of lib-y is normally restricted to `lib/` and `arch/*/lib`"
>
> > Add a custom rule to build lib.a, which is linked to the decompressor
> > for ARCH=x86, ARCH=arm.
> >
> > For ARCH=arm64, use obj-y to link objects to vmlinux in the ordinary
> > way.
> >
>
> The code works perfectly fine as is, and I don't see what is
> fundamentally wrong with using static libraries outside of lib/ and
> arch/*/lib.
The intended usage of lib-y is to hook lib.a
to scripts/vmlinux.sh via KBUILD_VMLINUX_LIBS.
This Makefile is just what you found to work.
>
> Also, I would like this code to still be incorporated as a static
> library into arm64 as well, so that only pieces that are actually
> needed are incorporated into the final image.
No.
It is not working like that because you set
lib.a to core-y.
All objects in core-y are always linked to vmlinux.
Thanks.
>
>
>
> > Signed-off-by: Masahiro Yamada <masahiroy@xxxxxxxxxx>
> > ---
> >
> > arch/arm64/Makefile | 1 -
> > drivers/firmware/efi/Makefile | 2 +-
> > drivers/firmware/efi/libstub/Makefile | 51 +++++++++++++++------------
> > 3 files changed, 30 insertions(+), 24 deletions(-)
> >
> > diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
> > index 650e1185c190..ab79b20efc8d 100644
> > --- a/arch/arm64/Makefile
> > +++ b/arch/arm64/Makefile
> > @@ -145,7 +145,6 @@ export TEXT_OFFSET
> >
> > core-y += arch/arm64/
> > libs-y := arch/arm64/lib/ $(libs-y)
> > -core-$(CONFIG_EFI_STUB) += $(objtree)/drivers/firmware/efi/libstub/lib.a
> >
> > # Default target when executing plain make
> > boot := arch/arm64/boot
> > diff --git a/drivers/firmware/efi/Makefile b/drivers/firmware/efi/Makefile
> > index 7a216984552b..317a05cd388b 100644
> > --- a/drivers/firmware/efi/Makefile
> > +++ b/drivers/firmware/efi/Makefile
> > @@ -20,7 +20,7 @@ obj-$(CONFIG_EFI_VARS_PSTORE) += efi-pstore.o
> > obj-$(CONFIG_UEFI_CPER) += cper.o
> > obj-$(CONFIG_EFI_RUNTIME_MAP) += runtime-map.o
> > obj-$(CONFIG_EFI_RUNTIME_WRAPPERS) += runtime-wrappers.o
> > -subdir-$(CONFIG_EFI_STUB) += libstub
> > +obj-$(CONFIG_EFI_STUB) += libstub/
> > obj-$(CONFIG_EFI_FAKE_MEMMAP) += fake_map.o
> > obj-$(CONFIG_EFI_BOOTLOADER_CONTROL) += efibc.o
> > obj-$(CONFIG_EFI_TEST) += test/
> > diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
> > index cce4a7436052..e4e9b17fa3b2 100644
> > --- a/drivers/firmware/efi/libstub/Makefile
> > +++ b/drivers/firmware/efi/libstub/Makefile
> > @@ -44,7 +44,7 @@ OBJECT_FILES_NON_STANDARD := y
> > # Prevents link failures: __sanitizer_cov_trace_pc() is not linked in.
> > KCOV_INSTRUMENT := n
> >
> > -lib-y := efi-stub-helper.o gop.o secureboot.o tpm.o \
> > +stub-obj-y := efi-stub-helper.o gop.o secureboot.o tpm.o \
> > file.o mem.o random.o randomalloc.o pci.o \
> > skip_spaces.o lib-cmdline.o lib-ctype.o \
> > alignedmem.o relocate.o vsprintf.o
> > @@ -55,15 +55,19 @@ efi-deps-y := fdt_rw.c fdt_ro.c fdt_wip.c fdt.c fdt_empty_tree.c fdt_sw.c
> > $(obj)/lib-%.o: $(srctree)/lib/%.c FORCE
> > $(call if_changed_rule,cc_o_c)
> >
> > -lib-$(CONFIG_EFI_GENERIC_STUB) += efi-stub.o fdt.o string.o \
> > +stub-obj-$(CONFIG_EFI_GENERIC_STUB) += efi-stub.o fdt.o string.o \
> > $(patsubst %.c,lib-%.o,$(efi-deps-y))
> >
> > -lib-$(CONFIG_ARM) += arm32-stub.o
> > -lib-$(CONFIG_ARM64) += arm64-stub.o
> > -lib-$(CONFIG_X86) += x86-stub.o
> > +stub-obj-$(CONFIG_ARM) += arm32-stub.o
> > +stub-obj-$(CONFIG_ARM64) += arm64-stub.o
> > +stub-obj-$(CONFIG_X86) += x86-stub.o
> > CFLAGS_arm32-stub.o := -DTEXT_OFFSET=$(TEXT_OFFSET)
> > CFLAGS_arm64-stub.o := -DTEXT_OFFSET=$(TEXT_OFFSET)
> >
> > +targets += $(stub-obj-y)
> > +stub-obj-y := $(patsubst %.o,%.stub.o, $(stub-obj-y))
> > +targets += $(stub-obj-y)
> > +
> > #
> > # For x86, bootloaders like systemd-boot or grub-efi do not zero-initialize the
> > # .bss section, so the .bss section of the EFI stub needs to be included in the
> > @@ -83,23 +87,6 @@ STUBCOPY_FLAGS-$(CONFIG_ARM) += --rename-section .data=.data.efistub \
> > --rename-section .bss=.bss.efistub,load,alloc
> > STUBCOPY_RELOC-$(CONFIG_ARM) := R_ARM_ABS
> >
> > -#
> > -# arm64 puts the stub in the kernel proper, which will unnecessarily retain all
> > -# code indefinitely unless it is annotated as __init/__initdata/__initconst etc.
> > -# So let's apply the __init annotations at the section level, by prefixing
> > -# the section names directly. This will ensure that even all the inline string
> > -# literals are covered.
> > -# The fact that the stub and the kernel proper are essentially the same binary
> > -# also means that we need to be extra careful to make sure that the stub does
> > -# not rely on any absolute symbol references, considering that the virtual
> > -# kernel mapping that the linker uses is not active yet when the stub is
> > -# executing. So build all C dependencies of the EFI stub into libstub, and do
> > -# a verification pass to see if any absolute relocations exist in any of the
> > -# object files.
> > -#
> > -extra-y := $(lib-y)
> > -lib-y := $(patsubst %.o,%.stub.o,$(lib-y))
> > -
> > STUBCOPY_FLAGS-$(CONFIG_ARM64) += --prefix-alloc-sections=.init \
> > --prefix-symbols=__efistub_
> > STUBCOPY_RELOC-$(CONFIG_ARM64) := R_AARCH64_ABS
> > @@ -121,3 +108,23 @@ quiet_cmd_stubcopy = STUBCPY $@
> > /bin/false; \
> > fi; \
> > $(OBJCOPY) $(STUBCOPY_FLAGS-y) $< $@
> > +
> > +# arm64 puts the stub in the kernel proper, which will unnecessarily retain all
> > +# code indefinitely unless it is annotated as __init/__initdata/__initconst etc.
> > +# So let's apply the __init annotations at the section level, by prefixing
> > +# the section names directly. This will ensure that even all the inline string
> > +# literals are covered.
> > +# The fact that the stub and the kernel proper are essentially the same binary
> > +# also means that we need to be extra careful to make sure that the stub does
> > +# not rely on any absolute symbol references, considering that the virtual
> > +# kernel mapping that the linker uses is not active yet when the stub is
> > +# executing. So build all C dependencies of the EFI stub into libstub, and do
> > +# a verification pass to see if any absolute relocations exist in any of the
> > +# object files.
> > +#
> > +obj-$(CONFIG_ARM64) += $(stub-obj-y)
> > +extra-$(CONFIG_ARM) += lib.a
> > +extra-$(CONFIG_X86) += lib.a
> > +
> > +$(obj)/lib.a: $(addprefix $(obj)/, $(stub-obj-y)) FORCE
> > + $(call if_changed,ar)
> > --
> > 2.25.1
> >
> >
> > _______________________________________________
> > linux-arm-kernel mailing list
> > linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
--
Best Regards
Masahiro Yamada
