6.16-stable review patch. If anyone has any objections, please let me know.
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From: Masahiro Yamada masahiroy@kernel.org
[ Upstream commit 344b6580472451390d070c65c27f59716a1deecb ]
When CONFIG_DEBUG_EFI is enabled, some objects are needlessly rebuilt.
[Steps to reproduce]
Enable CONFIG_DEBUG_EFI and run 'make' twice in a clean source tree. On the second run, arch/arm64/kernel/head.o is rebuilt even though no files have changed.
$ make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- clean $ make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- [ snip ] $ make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- CALL scripts/checksyscalls.sh AS arch/arm64/kernel/head.o AR arch/arm64/kernel/built-in.a AR arch/arm64/built-in.a AR built-in.a [ snip ]
The issue is caused by the use of the $(realpath ...) function.
At the time arch/arm64/kernel/Makefile is parsed on the first run, $(objtree)/vmlinux does not exist. As a result, $(realpath $(objtree)/vmlinux) expands to an empty string.
On the second run of Make, $(objtree)/vmlinux already exists, so $(realpath $(objtree)/vmlinux) expands to the absolute path of vmlinux. However, this change in the command line causes arch/arm64/kernel/head.o to be rebuilt.
To address this issue, use $(abspath ...) instead, which does not require the file to exist. While $(abspath ...) does not resolve symlinks, this should be fine from a debugging perspective.
The GNU Make manual [1] clearly explains the difference between the two:
$(realpath names...) For each file name in names return the canonical absolute name. A canonical name does not contain any . or .. components, nor any repeated path separators (/) or symlinks. In case of a failure the empty string is returned. Consult the realpath(3) documentation for a list of possible failure causes.
$(abspath namees...) For each file name in names return an absolute name that does not contain any . or .. components, nor any repeated path separators (/). Note that, in contrast to realpath function, abspath does not resolve symlinks and does not require the file names to refer to an existing file or directory. Use the wildcard function to test for existence.
The same problem exists in drivers/firmware/efi/libstub/Makefile.zboot. On the first run of Make, $(obj)/vmlinuz.efi.elf does not exist when the Makefile is parsed, so -DZBOOT_EFI_PATH is set to an empty string. Replace $(realpath ...) with $(abspath ...) there as well.
[1]: https://www.gnu.org/software/make/manual/make.html#File-Name-Functions
Fixes: 757b435aaabe ("efi: arm64: Add vmlinux debug link to the Image binary") Fixes: a050910972bb ("efi/libstub: implement generic EFI zboot") Signed-off-by: Masahiro Yamada masahiroy@kernel.org Acked-by: Ard Biesheuvel ardb@kernel.org Link: https://lore.kernel.org/r/20250625125555.2504734-1-masahiroy@kernel.org Signed-off-by: Will Deacon will@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- arch/arm64/kernel/Makefile | 2 +- drivers/firmware/efi/libstub/Makefile.zboot | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile index a2faf0049dab..76f32e424065 100644 --- a/arch/arm64/kernel/Makefile +++ b/arch/arm64/kernel/Makefile @@ -80,7 +80,7 @@ obj-y += head.o always-$(KBUILD_BUILTIN) += vmlinux.lds
ifeq ($(CONFIG_DEBUG_EFI),y) -AFLAGS_head.o += -DVMLINUX_PATH=""$(realpath $(objtree)/vmlinux)"" +AFLAGS_head.o += -DVMLINUX_PATH=""$(abspath vmlinux)"" endif
# for cleaning diff --git a/drivers/firmware/efi/libstub/Makefile.zboot b/drivers/firmware/efi/libstub/Makefile.zboot index 92e3c73502ba..832deee36e48 100644 --- a/drivers/firmware/efi/libstub/Makefile.zboot +++ b/drivers/firmware/efi/libstub/Makefile.zboot @@ -36,7 +36,7 @@ aflags-zboot-header-$(EFI_ZBOOT_FORWARD_CFI) := \ -DPE_DLL_CHAR_EX=IMAGE_DLLCHARACTERISTICS_EX_FORWARD_CFI_COMPAT
AFLAGS_zboot-header.o += -DMACHINE_TYPE=IMAGE_FILE_MACHINE_$(EFI_ZBOOT_MACH_TYPE) \ - -DZBOOT_EFI_PATH=""$(realpath $(obj)/vmlinuz.efi.elf)"" \ + -DZBOOT_EFI_PATH=""$(abspath $(obj)/vmlinuz.efi.elf)"" \ -DZBOOT_SIZE_LEN=$(zboot-size-len-y) \ -DCOMP_TYPE=""$(comp-type-y)"" \ $(aflags-zboot-header-y)