Re: [PATCH] efi/libstub: refactor Makefile to not use lib-y syntax

[Ard Biesheuvel <ardb@kernel.org>]

On Wed, 3 Jun 2020 at 07:34, Masahiro Yamada <masahiroy@kernel.org> 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?

> 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.

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.



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