linux-kernel - [PATCH 5.15 197/201] x86/extable: Prefer local labels in .set directives

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Date:   Wed, 27 Jul 2022 18:11:41 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Bernardo Meurer Costa <beme@...gle.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Nathan Chancellor <nathan@...nel.org>
Subject: [PATCH 5.15 197/201] x86/extable: Prefer local labels in .set directives

From: Nick Desaulniers <ndesaulniers@...gle.com>

commit 334865b2915c33080624e0d06f1c3e917036472c upstream.

Bernardo reported an error that Nathan bisected down to
(x86_64) defconfig+LTO_CLANG_FULL+X86_PMEM_LEGACY.

    LTO     vmlinux.o
  ld.lld: error: <instantiation>:1:13: redefinition of 'found'
  .set found, 0
              ^

  <inline asm>:29:1: while in macro instantiation
  extable_type_reg reg=%eax, type=(17 | ((0) << 16))
  ^

This appears to be another LTO specific issue similar to what was folded
into commit 4b5305decc84 ("x86/extable: Extend extable functionality"),
where the `.set found, 0` in DEFINE_EXTABLE_TYPE_REG in
arch/x86/include/asm/asm.h conflicts with the symbol for the static
function `found` in arch/x86/kernel/pmem.c.

Assembler .set directive declare symbols with global visibility, so the
assembler may not rename such symbols in the event of a conflict. LTO
could rename static functions if there was a conflict in C sources, but
it cannot see into symbols defined in inline asm.

The symbols are also retained in the symbol table, regardless of LTO.

Give the symbols .L prefixes making them locally visible, so that they
may be renamed for LTO to avoid conflicts, and to drop them from the
symbol table regardless of LTO.

Fixes: 4b5305decc84 ("x86/extable: Extend extable functionality")
Reported-by: Bernardo Meurer Costa <beme@...gle.com>
Debugged-by: Nathan Chancellor <nathan@...nel.org>
Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Nathan Chancellor <nathan@...nel.org>
Tested-by: Nathan Chancellor <nathan@...nel.org>
Link: https://lore.kernel.org/r/20220329202148.2379697-1-ndesaulniers@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/x86/include/asm/asm.h |   20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

--- a/arch/x86/include/asm/asm.h
+++ b/arch/x86/include/asm/asm.h
@@ -149,24 +149,24 @@
 
 # define DEFINE_EXTABLE_TYPE_REG \
 	".macro extable_type_reg type:req reg:req\n"						\
-	".set found, 0\n"									\
-	".set regnr, 0\n"									\
+	".set .Lfound, 0\n"									\
+	".set .Lregnr, 0\n"									\
 	".irp rs,rax,rcx,rdx,rbx,rsp,rbp,rsi,rdi,r8,r9,r10,r11,r12,r13,r14,r15\n"		\
 	".ifc \\reg, %%\\rs\n"									\
-	".set found, found+1\n"									\
-	".long \\type + (regnr << 8)\n"								\
+	".set .Lfound, .Lfound+1\n"								\
+	".long \\type + (.Lregnr << 8)\n"							\
 	".endif\n"										\
-	".set regnr, regnr+1\n"									\
+	".set .Lregnr, .Lregnr+1\n"								\
 	".endr\n"										\
-	".set regnr, 0\n"									\
+	".set .Lregnr, 0\n"									\
 	".irp rs,eax,ecx,edx,ebx,esp,ebp,esi,edi,r8d,r9d,r10d,r11d,r12d,r13d,r14d,r15d\n"	\
 	".ifc \\reg, %%\\rs\n"									\
-	".set found, found+1\n"									\
-	".long \\type + (regnr << 8)\n"								\
+	".set .Lfound, .Lfound+1\n"								\
+	".long \\type + (.Lregnr << 8)\n"							\
 	".endif\n"										\
-	".set regnr, regnr+1\n"									\
+	".set .Lregnr, .Lregnr+1\n"								\
 	".endr\n"										\
-	".if (found != 1)\n"									\
+	".if (.Lfound != 1)\n"									\
 	".error \"extable_type_reg: bad register argument\"\n"					\
 	".endif\n"										\
 	".endm\n"