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| author | Nick Desaulniers <ndesaulniers@google.com> | 2021-01-12 11:46:24 -0800 |
|---|---|---|
| committer | Borislav Petkov <bp@suse.de> | 2021-01-14 17:18:25 +0100 |
| commit | 5e6dca82bcaa49348f9e5fcb48df4881f6d6c4ae (patch) | |
| tree | a04ed97a7888347804f1e9a4c2cf61fa62dc6ad9 /arch/x86/entry/thunk_64.S | |
| parent | 7c53f6b671f4aba70ff15e1b05148b10d58c2837 (diff) | |
| download | linux-5e6dca82bcaa49348f9e5fcb48df4881f6d6c4ae.tar.bz2 | |
x86/entry: Emit a symbol for register restoring thunk
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 (Clang's integrated assembler). Josh
notes:
With the LLVM assembler not generating section symbols, objtool has no
way to reference this code when it generates ORC unwinder entries,
because this code is outside of any ELF function.
The limitation now being imposed by objtool is that all code must be
contained in an ELF symbol. And .L symbols don't create such symbols.
So basically, you can use an .L symbol *inside* a function or a code
segment, you just can't use the .L symbol to contain the code using a
SYM_*_START/END annotation pair.
Fangrui notes that this optimization is helpful for reducing image size
when compiling with -ffunction-sections and -fdata-sections. I have
observed 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
of not generating unused section symbols ([1]), so this will
also become a problem for users of GNU binutils once they upgrade to 2.36.
Omit the .L prefix on a label so that the assembler will emit an entry
into the symbol table for the label, with STB_LOCAL binding. This
enables objtool to generate proper unwind info here with LLVM_IAS=1 or
GNU binutils 2.36+.
[ bp: Massage commit message. ]
Reported-by: Arnd Bergmann <arnd@arndb.de>
Suggested-by: Josh Poimboeuf <jpoimboe@redhat.com>
Suggested-by: Borislav Petkov <bp@alien8.de>
Suggested-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lkml.kernel.org/r/20210112194625.4181814-1-ndesaulniers@google.com
Link: https://github.com/ClangBuiltLinux/linux/issues/1209
Link: https://reviews.llvm.org/D93783
Link: https://sourceware.org/binutils/docs/as/Symbol-Names.html
Link: https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=d1bcae833b32f1408485ce69f844dcd7ded093a8 [1]
Diffstat (limited to 'arch/x86/entry/thunk_64.S')
| -rw-r--r-- | arch/x86/entry/thunk_64.S | 8 |
1 files changed, 4 insertions, 4 deletions
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 |