On Mon, 18 Dec 2023 at 09:01, Masahiro Yamada <masahiroy@xxxxxxxxxx> wrote: > > You do not need to use $(shell ...) in recipe lines, as they are already > executed in a shell. An alternative solution is $$(...), which is an > escaped sequence of the shell's command substituion, $(...). > > For this case, there is a reason to avoid $(shell ...). > > Kbuild detects command changes by using the if_changed macro, which > compares the previous command recorded in .*.cmd with the current > command from Makefile. If they differ, Kbuild re-runs the build rule. > > To diff the commands, Make must expand $(shell ...) first. It means that > hexdump is executed every time, even when nothing needs rebuilding. If > Kbuild determines that vmlinux.bin needs rebuilding, hexdump will be > executed again to evaluate the 'cmd' macro, one more time to really > build vmlinux.bin, and finally yet again to record the expanded command > into .*.cmd. > > Replace $(shell ...) with $$(...) to avoid multiple, unnecessay shell > evaluations. Since Make is agnostic about the shell code, $(...), the > if_changed macro compares the string "$(hexdump -s16 -n4 ...)" verbatim, > so hexdump is run only for building vmlinux.bin. > > For the same reason, $(shell ...) in EFI_ZBOOT_OBJCOPY_FLAGS should be > eliminated. > > While I was here, I replaced '&&' with ';' because a command for > if_changed is executed with 'set -e'. > > Signed-off-by: Masahiro Yamada <masahiroy@xxxxxxxxxx> Reviewed-by: Ard Biesheuvel <ardb@xxxxxxxxxx> > --- > > arch/arm64/boot/Makefile | 2 +- > drivers/firmware/efi/libstub/Makefile.zboot | 4 ++-- > 2 files changed, 3 insertions(+), 3 deletions(-) > > diff --git a/arch/arm64/boot/Makefile b/arch/arm64/boot/Makefile > index 1761f5972443..a5a787371117 100644 > --- a/arch/arm64/boot/Makefile > +++ b/arch/arm64/boot/Makefile > @@ -44,7 +44,7 @@ EFI_ZBOOT_BFD_TARGET := elf64-littleaarch64 > EFI_ZBOOT_MACH_TYPE := ARM64 > EFI_ZBOOT_FORWARD_CFI := $(CONFIG_ARM64_BTI_KERNEL) > > -EFI_ZBOOT_OBJCOPY_FLAGS = --add-symbol zboot_code_size=0x$(shell \ > +EFI_ZBOOT_OBJCOPY_FLAGS = --add-symbol zboot_code_size=0x$$( \ > $(NM) vmlinux|grep _kernel_codesize|cut -d' ' -f1) > > include $(srctree)/drivers/firmware/efi/libstub/Makefile.zboot > diff --git a/drivers/firmware/efi/libstub/Makefile.zboot b/drivers/firmware/efi/libstub/Makefile.zboot > index 2c489627a807..65ffd0b760b2 100644 > --- a/drivers/firmware/efi/libstub/Makefile.zboot > +++ b/drivers/firmware/efi/libstub/Makefile.zboot > @@ -5,8 +5,8 @@ > # EFI_ZBOOT_FORWARD_CFI > > quiet_cmd_copy_and_pad = PAD $@ > - cmd_copy_and_pad = cp $< $@ && \ > - truncate -s $(shell hexdump -s16 -n4 -e '"%u"' $<) $@ > + cmd_copy_and_pad = cp $< $@; \ > + truncate -s $$(hexdump -s16 -n4 -e '"%u"' $<) $@ > > # Pad the file to the size of the uncompressed image in memory, including BSS > $(obj)/vmlinux.bin: $(obj)/$(EFI_ZBOOT_PAYLOAD) FORCE > -- > 2.40.1 > >
