| Message ID | 20211213224914.1501303-3-paul@crapouillou.net (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | MIPS: Add support for LTO | expand |
On Mon, Dec 13, 2021 at 10:49:13PM +0000, Paul Cercueil wrote: > We need a valid ELF object for dummy.o, so that objcopy can insert the > vmlinuz payload. > > Therefore, we must build the decompresser program without LTO, otherwise > dummy.o will be LLVM bytecode instead of a ELF object file. > > Building the decompresser with LTO wouldn't make much sense anyway, > unlike building the vmlinuz itself with LTO. > > Signed-off-by: Paul Cercueil <paul@crapouillou.net> Seems reasonable. Reviewed-by: Nathan Chancellor <nathan@kernel.org> > --- > arch/mips/boot/compressed/Makefile | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/arch/mips/boot/compressed/Makefile b/arch/mips/boot/compressed/Makefile > index 4c9ecfbb0ef4..2d01c50fb0b1 100644 > --- a/arch/mips/boot/compressed/Makefile > +++ b/arch/mips/boot/compressed/Makefile > @@ -27,6 +27,9 @@ ifdef CONFIG_CPU_LOONGSON64 > KBUILD_CFLAGS := $(filter-out -march=loongson3a, $(KBUILD_CFLAGS)) -march=mips64r2 > endif > > +# Disable LTO > +KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_LTO), $(KBUILD_CFLAGS)) > + > KBUILD_CFLAGS := $(KBUILD_CFLAGS) -mno-abicalls -D__KERNEL__ -D__DISABLE_EXPORTS \ > -DBOOT_HEAP_SIZE=$(BOOT_HEAP_SIZE) -D"VMLINUX_LOAD_ADDRESS_ULL=$(VMLINUX_LOAD_ADDRESS)ull" > > -- > 2.33.0 > >
On Mon, Dec 13, 2021 at 2:49 PM Paul Cercueil <paul@crapouillou.net> wrote: > > We need a valid ELF object for dummy.o, so that objcopy can insert the > vmlinuz payload. > > Therefore, we must build the decompresser program without LTO, otherwise > dummy.o will be LLVM bytecode instead of a ELF object file. While the below may work and follows the pattern observed in drivers/firmware/efi/libstub/Makefile 43:KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_LTO), $(KBUILD_CFLAGS)) I can't help but wonder whether we should instead be doing something like: arch/x86/power/Makefile 9:CFLAGS_REMOVE_cpu.o := $(CC_FLAGS_LTO) scripts/mod/Makefile 3:CFLAGS_REMOVE_empty.o += $(CC_FLAGS_LTO) drivers/misc/lkdtm/Makefile 19:CFLAGS_REMOVE_rodata.o += $(CC_FLAGS_LTO) but for dummy.o? ie. CFLAGS_REMOVE_dummy.o += $(CC_FLAGS_LTO) Can you please try that rather than disabling LTO for a large subset of files? > > Building the decompresser with LTO wouldn't make much sense anyway, > unlike building the vmlinuz itself with LTO. Why not? We do it for x86 and arm64 AFAICT. > > Signed-off-by: Paul Cercueil <paul@crapouillou.net> > --- > arch/mips/boot/compressed/Makefile | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/arch/mips/boot/compressed/Makefile b/arch/mips/boot/compressed/Makefile > index 4c9ecfbb0ef4..2d01c50fb0b1 100644 > --- a/arch/mips/boot/compressed/Makefile > +++ b/arch/mips/boot/compressed/Makefile > @@ -27,6 +27,9 @@ ifdef CONFIG_CPU_LOONGSON64 > KBUILD_CFLAGS := $(filter-out -march=loongson3a, $(KBUILD_CFLAGS)) -march=mips64r2 > endif > > +# Disable LTO > +KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_LTO), $(KBUILD_CFLAGS)) > + > KBUILD_CFLAGS := $(KBUILD_CFLAGS) -mno-abicalls -D__KERNEL__ -D__DISABLE_EXPORTS \ > -DBOOT_HEAP_SIZE=$(BOOT_HEAP_SIZE) -D"VMLINUX_LOAD_ADDRESS_ULL=$(VMLINUX_LOAD_ADDRESS)ull" > > -- > 2.33.0 >
diff --git a/arch/mips/boot/compressed/Makefile b/arch/mips/boot/compressed/Makefile index 4c9ecfbb0ef4..2d01c50fb0b1 100644 --- a/arch/mips/boot/compressed/Makefile +++ b/arch/mips/boot/compressed/Makefile @@ -27,6 +27,9 @@ ifdef CONFIG_CPU_LOONGSON64 KBUILD_CFLAGS := $(filter-out -march=loongson3a, $(KBUILD_CFLAGS)) -march=mips64r2 endif +# Disable LTO +KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_LTO), $(KBUILD_CFLAGS)) + KBUILD_CFLAGS := $(KBUILD_CFLAGS) -mno-abicalls -D__KERNEL__ -D__DISABLE_EXPORTS \ -DBOOT_HEAP_SIZE=$(BOOT_HEAP_SIZE) -D"VMLINUX_LOAD_ADDRESS_ULL=$(VMLINUX_LOAD_ADDRESS)ull"
We need a valid ELF object for dummy.o, so that objcopy can insert the vmlinuz payload. Therefore, we must build the decompresser program without LTO, otherwise dummy.o will be LLVM bytecode instead of a ELF object file. Building the decompresser with LTO wouldn't make much sense anyway, unlike building the vmlinuz itself with LTO. Signed-off-by: Paul Cercueil <paul@crapouillou.net> --- arch/mips/boot/compressed/Makefile | 3 +++ 1 file changed, 3 insertions(+)