x86/extable: Prefer local labels in .set directives
authorNick Desaulniers <ndesaulniers@google.com>
Tue, 29 Mar 2022 20:21:45 +0000 (13:21 -0700)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Fri, 29 Jul 2022 15:25:33 +0000 (17:25 +0200)
commitb6c24afba608b9faed82bd24a3adf2efac269f73
tree77471f4d0794e7d23f336e903ca99588d222f4b4
parentf85a6046f7718f11c6ad015a0ba25d897194b1ac
x86/extable: Prefer local labels in .set directives

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@google.com>
Debugged-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Link: https://lore.kernel.org/r/20220329202148.2379697-1-ndesaulniers@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
arch/x86/include/asm/asm.h