On Sat, Jan 08, 2022 at 12:49:04PM +0100, Ingo Molnar wrote: > > * Nathan Chancellor <nathan@xxxxxxxxxx> wrote: > > > 5. Build error in arch/arm64/kvm/hyp/nvhe with LTO > > > > With arm64 + CONFIG_LTO_CLANG_THIN=y, I see: > > > > $ make -skj"$(nproc)" ARCH=arm64 LLVM=1 defconfig > > > > $ scripts/config -e LTO_CLANG_THIN > > > > $ make -skj"$(nproc)" ARCH=arm64 LLVM=1 olddefconfig arch/arm64/kvm/hyp/nvhe/ > > ld.lld: error: arch/arm64/kvm/hyp/nvhe/hyp.lds:2: unknown directive: .macro > > >>> .macro __put, val, name > > >>> ^ > > make[5]: *** [arch/arm64/kvm/hyp/nvhe/Makefile:51: arch/arm64/kvm/hyp/nvhe/kvm_nvhe.tmp.o] Error 1 > > > > I was not able to figure out the exact include chain but CONFIG_LTO > > causes asm/alternative-macros.h to be included in asm/rwonce.h, which > > eventually gets included in either asm/cache.h or asm/memory.h. > > > > I managed to solve this with the following diff but I am not sure if > > there is a better or cleaner way to do that. > > > > diff --git a/arch/arm64/include/asm/rwonce.h b/arch/arm64/include/asm/rwonce.h > > index 1bce62fa908a..e19572a205d0 100644 > > --- a/arch/arm64/include/asm/rwonce.h > > +++ b/arch/arm64/include/asm/rwonce.h > > @@ -5,7 +5,7 @@ > > #ifndef __ASM_RWONCE_H > > #define __ASM_RWONCE_H > > > > -#ifdef CONFIG_LTO > > +#if defined(CONFIG_LTO) && !defined(LINKER_SCRIPT) > > > > #include <linux/compiler_types.h> > > #include <asm/alternative-macros.h> > > @@ -66,7 +66,7 @@ > > }) > > > > #endif /* !BUILD_VDSO */ > > -#endif /* CONFIG_LTO */ > > +#endif /* CONFIG_LTO && !LINKER_SCRIPT */ > > So the error message suggests that the linker script somehow ends up > including asm-generic/export.h: > > kepler:~/mingo.tip.git> git grep 'macro __put' > include/asm-generic/export.h:.macro __put, val, name > > ? Correct. > But I'd guess that similar to the __ASSEMBLY__ patterns we have in headers, > not including the rwonce.h bits if LINKER_SCRIPT is defined is probably > close to the right solution - but it would also know how such a low level > header ended up in a linker script. Might have been to pick up some offset > or size definition somewhere? > > I.e. how did the build end up including asm/rwonce.h? > > You can generally debug such weird dependency chains by putting a > debug #warning into the affected header - such as the patch below. > > This prints a stack of the header dependencies: > > CC kernel/sched/core.o > In file included from ./include/linux/compiler.h:263, > from ./include/linux/static_call_types.h:7, > from ./include/linux/kernel.h:6, > from ./include/linux/highmem.h:5, > from kernel/sched/core.c:9: > ./arch/arm64/include/asm/rwonce.h:8:2: warning: #warning debug [-Wcpp] > 8 | #warning debug > > ... and should in principle also work in the linker script context. Neat trick! I added #ifdef LINKER_SCRIPT #warning debug #endif to arch/arm64/include/asm/rwonce.h and built with ThinLTO, which reveals: $ make -skj"$(nproc)" ARCH=arm64 LLVM=1 defconfig $ scripts/config -d LTO_NONE -e LTO_CLANG_THIN $ make -skj"$(nproc)" ARCH=arm64 LLVM=1 olddefconfig arch/arm64/kvm/hyp/ In file included from arch/arm64/kvm/hyp/nvhe/hyp.lds.S:12: In file included from ./arch/arm64/include/asm/memory.h:18: In file included from ./arch/arm64/include/asm/thread_info.h:11: In file included from ./include/linux/compiler.h:263: ./arch/arm64/include/asm/rwonce.h:9:2: warning: debug [-W#warnings] #warning debug ^ 1 warning generated. I wonder if the compiler.h include could be broken up? I removed it altogether just to see what would break and defconfig, defconfig + CONFIG_LTO_CLANG_THIN=y, and allmodconfig all continue to build. Cheers, Nathan
