lkml.org 
[lkml]   [2020]   [Dec]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
Subject[PATCH] x86/entry: use STB_GLOBAL for register restoring thunk
From
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.

This behavior was implemented as an optimization in LLVM 5 years ago,
but it's not the first time this has caused issues for objtool. A patch
has been authored against LLVM to revert the behavior, which may or may
not be accepted. Until then use a global symbol for the thunk that way
objtool can generate proper unwind info here with LLVM_IAS=1.

Cc: Fangrui Song <maskray@google.com>
Reported-by: Arnd Bergmann <arnd@arndb.de>
Suggested-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://github.com/ClangBuiltLinux/linux/issues/1209
Link: https://reviews.llvm.org/D93783
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
---
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
\
 
 \ /
  Last update: 2020-12-24 00:23    [W:0.063 / U:5.892 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site