Messages in this thread Patch in this message | | | Date | Tue, 5 Jan 2021 19:58:10 -0600 | From | Josh Poimboeuf <> | Subject | Re: [PATCH v2] x86/entry: use STB_GLOBAL for register restoring thunk |
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On Tue, Jan 05, 2021 at 04:43:51PM -0800, Nick Desaulniers wrote: > 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.
On second thought, there's no need to make the symbol global. Just getting rid of the '.L' local label symbol prefix should be enough to make an ELF symbol:
diff --git a/arch/x86/entry/thunk_64.S b/arch/x86/entry/thunk_64.S index ccd32877a3c4..c9a9fbf1655f 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_LOCAL_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
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