From: Nick Desaulniers <ndesaulniers@google.com>
To: Andy Lutomirski <luto@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>
Cc: Nick Desaulniers <ndesaulniers@google.com>,
Fangrui Song <maskray@google.com>, Arnd Bergmann <arnd@arndb.de>,
Josh Poimboeuf <jpoimboe@redhat.com>,
x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
Nathan Chancellor <natechancellor@gmail.com>,
linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com
Subject: [PATCH v3] x86/entry: emit a symbol for register restoring thunk
Date: Mon, 11 Jan 2021 12:38:06 -0800 [thread overview]
Message-ID: <20210111203807.3547278-1-ndesaulniers@google.com> (raw)
In-Reply-To: <20210106015810.5p6crnh7jqtmjtv4@treble>
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 optimization 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].
We can omit the .L prefix on a label to 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.
Cc: Fangrui Song <maskray@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/pipermail/binutils/2020-December/114671.html
Reported-by: Arnd Bergmann <arnd@arndb.de>
Suggested-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
---
Changes v2 -> v3:
* rework to use STB_LOCAL rather than STB_GLOBAL by dropping .L prefix,
as per Josh.
* rename oneline to drop STB_GLOBAL in commit message.
* add link to GAS docs on .L prefix.
* drop Josh's ack since patch changed.
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..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
--
2.30.0.284.gd98b1dd5eaa7-goog
next prev parent reply other threads:[~2021-01-11 20:39 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-23 23:21 [PATCH] x86/entry: use STB_GLOBAL for register restoring thunk Nick Desaulniers
2020-12-24 4:55 ` Josh Poimboeuf
2021-01-06 0:43 ` [PATCH v2] " Nick Desaulniers
2021-01-06 1:58 ` Josh Poimboeuf
2021-01-11 20:38 ` Nick Desaulniers [this message]
2021-01-11 20:58 ` [PATCH v3] x86/entry: emit a symbol " Fangrui Song
2021-01-11 22:09 ` Josh Poimboeuf
2021-01-11 22:16 ` Fāng-ruì Sòng
2021-01-11 22:12 ` Josh Poimboeuf
2021-01-12 0:38 ` Borislav Petkov
2021-01-12 0:41 ` Fāng-ruì Sòng
2021-01-12 1:00 ` Borislav Petkov
2021-01-12 1:13 ` Nick Desaulniers
2021-01-12 1:59 ` Josh Poimboeuf
2021-01-12 11:54 ` Borislav Petkov
2021-01-12 19:46 ` [PATCH v4] " Nick Desaulniers
2021-01-12 21:01 ` Mark Brown
2021-01-13 16:59 ` Josh Poimboeuf
2021-01-13 17:46 ` [PATCH] Documentation: asm-annotation: clarify .L local symbol names Nick Desaulniers
2021-01-13 19:56 ` Mark Brown
2021-01-13 17:56 ` [PATCH v4] x86/entry: emit a symbol for register restoring thunk Nick Desaulniers
2021-01-14 10:39 ` Borislav Petkov
2021-01-14 11:36 ` Peter Zijlstra
2021-01-14 13:28 ` [PATCH] x86/entry: Remove put_ret_addr_in_rdi THUNK macro argument Borislav Petkov
2021-01-14 15:53 ` Peter Zijlstra
2021-01-19 10:12 ` [tip: x86/entry] " tip-bot2 for Borislav Petkov
2021-01-14 15:14 ` [PATCH v4] x86/entry: emit a symbol for register restoring thunk Josh Poimboeuf
2021-01-14 11:49 ` [Linux-kernel-mentees] Fwd: " Lukas Bulwahn
2021-01-14 14:21 ` Aditya
2021-01-14 14:35 ` Lukas Bulwahn
2021-01-13 11:52 ` [tip: x86/entry] x86/entry: Emit " tip-bot2 for Nick Desaulniers
2021-01-19 10:12 ` tip-bot2 for Nick Desaulniers
2021-01-12 11:47 ` [PATCH v3] x86/entry: emit " Borislav Petkov
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