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Revert "[AArch64][BZ #17711] Fix extern protected data handling"

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This reverts commit 0910702c4d.

Say both a.so and b.so define protected data symbol `var` and the executable
copy relocates var.  ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA has strange
semantics: a.so accesses the copy in the executable while b.so accesses its
own.  This behavior requires that (a) the compiler emits GOT-generating
relocations (b) the linker produces GLOB_DAT instead of RELATIVE.

Without the ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA code, b.so's GLOB_DAT
will bind to the executable (normal behavior).

For aarch64 it makes sense to restore the original behavior and don't
pay the ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA cost.  The behavior is very
unlikely used by anyone.

* Clang code generator treats STV_PROTECTED the same way as STV_HIDDEN:
  no GOT-generating relocation in the first place.
* gold and lld reject copy relocation on a STV_PROTECTED symbol.
* Nowadays -fpie/-fpic modes are popular.  GCC/Clang's codegen uses
  GOT-generating relocation when accessing an default visibility
  external symbol which avoids copy relocation.

Reviewed-by: Szabolcs Nagy <szabolcs.nagy@arm.com>
This commit is contained in:
Fangrui Song 2022-05-23 13:37:05 -07:00
parent a8b11bd1f8
commit e555954e02
2 changed files with 6 additions and 28 deletions
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13
sysdeps/aarch64/dl-machine.h
View File

@ -109,13 +109,12 @@ elf_machine_runtime_setup (struct link_map *l, struct r_scope_elem *scope[],
#define RTLD_START asm (".globl _dl_start");
#define elf_machine_type_class(type) \
((((type) == AARCH64_R(JUMP_SLOT) \
|| (type) == AARCH64_R(TLS_DTPMOD) \
|| (type) == AARCH64_R(TLS_DTPREL) \
|| (type) == AARCH64_R(TLS_TPREL) \
|| (type) == AARCH64_R(TLSDESC)) * ELF_RTYPE_CLASS_PLT) \
| (((type) == AARCH64_R(COPY)) * ELF_RTYPE_CLASS_COPY) \
| (((type) == AARCH64_R(GLOB_DAT)) * ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA))
((((type) == R_AARCH64_JUMP_SLOT || \
(type) == R_AARCH64_TLS_DTPMOD || \
(type) == R_AARCH64_TLS_DTPREL || \
(type) == R_AARCH64_TLS_TPREL || \
(type) == R_AARCH64_TLSDESC) * ELF_RTYPE_CLASS_PLT) \
| (((type) == R_AARCH64_COPY) * ELF_RTYPE_CLASS_COPY))
#define ELF_MACHINE_JMP_SLOT AARCH64_R(JUMP_SLOT)

21
sysdeps/aarch64/dl-sysdep.h
View File

@ -1,21 +0,0 @@
/* Copyright (C) 2002-2022 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public License as
published by the Free Software Foundation; either version 2.1 of the
License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include_next <dl-sysdep.h>
#define DL_EXTERN_PROTECTED_DATA