cfi: ld.lld: warning: <internal>:(.eh_frame) is being placed in '.eh_frame'

[dileks]

CC @samitolvanen @MaskRay

I pulled in cfi-5.10 releases tag on top of Linux v5.10.3.

My LLVM toolchain is version 11.0.1-rc2.

Note: CFI (and LTO) feature requires LLVM=1 and LLVM_IAS=1 to be used and LLVM toolchain >= v11 (see CONFIG_HAS_LTO_CLANG).

In my logs I see (beyond usual known CFI warnings):

+ ld.lld-11 -m elf_x86_64 --thinlto-cache-dir=.thinlto-cache -mllvm -import-instr-limit=5 --emit-relocs --discard-none -z max-page-size=0x200000 --build-id=sha1 -X --orphan-handling=warn --strip-debug -o .tmp_vmlinux.kallsyms1 -T ./arch/x86/kernel/vmlinux.lds --whole-archive vmlinux.o --no-whole-archive
ld.lld-11: warning: <internal>:(.eh_frame) is being placed in '.eh_frame'
+ kallsyms .tmp_vmlinux.kallsyms1 .tmp_vmlinux.kallsyms1.S

+ ld.lld-11 -m elf_x86_64 --thinlto-cache-dir=.thinlto-cache -mllvm -import-instr-limit=5 --emit-relocs --discard-none -z max-page-size=0x200000 --build-id=sha1 -X --orphan-handling=warn --strip-debug -o .tmp_vmlinux.kallsyms2 -T ./arch/x86/kernel/vmlinux.lds --whole-archive vmlinux.o --no-whole-archive .tmp_vmlinux.kallsyms1.o
ld.lld-11: warning: <internal>:(.eh_frame) is being placed in '.eh_frame'
+ kallsyms .tmp_vmlinux.kallsyms2 .tmp_vmlinux.kallsyms2.S

+ ld.lld-11 -m elf_x86_64 --thinlto-cache-dir=.thinlto-cache -mllvm -import-instr-limit=5 --emit-relocs --discard-none -z max-page-size=0x200000 --build-id=sha1 -X --orphan-handling=warn -o vmlinux -T ./arch/x86/kernel/vmlinux.lds --whole-archive vmlinux.o --no-whole-archive .tmp_vmlinux.kallsyms2.o
ld.lld-11: warning: <internal>:(.eh_frame) is being placed in '.eh_frame'

Link: https://github.com/samitolvanen/linux/releases/tag/cfi-5.10

[dileks]

Feel free to change subject and labels.

[samitolvanen]

Thanks for filing the issue. I also see this on arm64 builds and with ToT LLVM.

[nickdesaulniers]

These warnings are coming from the linker flag --orphan-handling=warn. It seems the linker scripts being passed after -T maybe don't mention where to place these sections explicitly? Usually we disable .eh_frame via -fno-asynchronous-unwind-tables (https://stackoverflow.com/a/26302715/1027966).

[samitolvanen]

As Nathan pointed out in issue #1069, defining SANITIZER_DISCARDS also with CONFIG_CFI_CLANG removes the warning. This is now fixed in the current CFI trees.