Arnd found a randconfig that produces the warning: arch/x86/entry/thunk_64.o: warning: objtool: missing symbol for insn at offset 0x3e
when building with LLVM_IAS=1 (use Clang's integrated assembler). Josh notes: With the LLVM assembler stripping the .text section symbol, objtool has no way to reference this code when it generates ORC unwinder entries, because this code is outside of any ELF function. Fangrui notes that this is helpful for reducing images size when compiling with -ffunction-sections and -fdata-sections. I have observerd on the order of tens of thousands of symbols for the kernel images built with those flags. A patch has been authored against GNU binutils to match this behavior, with a new flag --generate-unused-section-symbols=[yes|no]. Use a global symbol for the thunk that way objtool can generate proper unwind info here with LLVM_IAS=1. Cc: Fangrui Song <[email protected]> Link: https://github.com/ClangBuiltLinux/linux/issues/1209 Link: https://reviews.llvm.org/D93783 Link: https://sourceware.org/pipermail/binutils/2020-December/114671.html Reported-by: Arnd Bergmann <[email protected]> Suggested-by: Josh Poimboeuf <[email protected]> Acked-by: Josh Poimboeuf <[email protected]> Signed-off-by: Nick Desaulniers <[email protected]> --- Changes v1 -> v2: * Pick up Josh's Ack. * Add commit message info about -ffunction-sections/-fdata-sections, and link to binutils patch. arch/x86/entry/thunk_64.S | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/arch/x86/entry/thunk_64.S b/arch/x86/entry/thunk_64.S index ccd32877a3c4..878816034a73 100644 --- a/arch/x86/entry/thunk_64.S +++ b/arch/x86/entry/thunk_64.S @@ -31,7 +31,7 @@ SYM_FUNC_START_NOALIGN(\name) .endif call \func - jmp .L_restore + jmp __thunk_restore SYM_FUNC_END(\name) _ASM_NOKPROBE(\name) .endm @@ -44,7 +44,7 @@ SYM_FUNC_END(\name) #endif #ifdef CONFIG_PREEMPTION -SYM_CODE_START_LOCAL_NOALIGN(.L_restore) +SYM_CODE_START_NOALIGN(__thunk_restore) popq %r11 popq %r10 popq %r9 @@ -56,6 +56,6 @@ SYM_CODE_START_LOCAL_NOALIGN(.L_restore) popq %rdi popq %rbp ret - _ASM_NOKPROBE(.L_restore) -SYM_CODE_END(.L_restore) + _ASM_NOKPROBE(__thunk_restore) +SYM_CODE_END(__thunk_restore) #endif -- 2.29.2.729.g45daf8777d-goog
