139 lines
5.4 KiB
Diff
139 lines
5.4 KiB
Diff
commit 82bc69c012838a381c4167c156a06f4598f34227
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Author: Szabolcs Nagy <szabolcs.nagy@arm.com>
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Date: Thu Apr 25 15:35:35 2019 +0100
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aarch64: handle STO_AARCH64_VARIANT_PCS
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Avoid lazy binding of symbols that may follow a variant PCS with different
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register usage convention from the base PCS.
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Currently the lazy binding entry code does not preserve all the registers
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required for AdvSIMD and SVE vector calls. Saving and restoring all
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registers unconditionally may break existing binaries, even if they never
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use vector calls, because of the larger stack requirement for lazy
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resolution, which can be significant on an SVE system.
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The solution is to mark all symbols in the symbol table that may follow
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a variant PCS so the dynamic linker can handle them specially. In this
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patch such symbols are always resolved at load time, not lazily.
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So currently LD_AUDIT for variant PCS symbols are not supported, for that
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the _dl_runtime_profile entry needs to be changed e.g. to unconditionally
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save/restore all registers (but pass down arg and retval registers to
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pltentry/exit callbacks according to the base PCS).
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This patch also removes a __builtin_expect from the modified code because
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the branch prediction hint did not seem useful.
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* sysdeps/aarch64/dl-dtprocnum.h: New file.
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* sysdeps/aarch64/dl-machine.h (DT_AARCH64): Define.
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(elf_machine_runtime_setup): Handle DT_AARCH64_VARIANT_PCS.
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(elf_machine_lazy_rel): Check STO_AARCH64_VARIANT_PCS and bind such
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symbols at load time.
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* sysdeps/aarch64/linkmap.h (struct link_map_machine): Add variant_pcs.
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diff --git a/sysdeps/aarch64/dl-dtprocnum.h b/sysdeps/aarch64/dl-dtprocnum.h
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new file mode 100644
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index 0000000000000000..4ac2adf23458e02d
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--- /dev/null
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+++ b/sysdeps/aarch64/dl-dtprocnum.h
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@@ -0,0 +1,21 @@
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+/* Configuration of lookup functions. AArch64 version.
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+ Copyright (C) 2019 Free Software Foundation, Inc.
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+ This file is part of the GNU C Library.
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+
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+ The GNU C Library is free software; you can redistribute it and/or
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+ modify it under the terms of the GNU Lesser General Public
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+ License as published by the Free Software Foundation; either
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+ version 2.1 of the License, or (at your option) any later version.
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+
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+ The GNU C Library is distributed in the hope that it will be useful,
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+ but WITHOUT ANY WARRANTY; without even the implied warranty of
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+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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+ Lesser General Public License for more details.
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+
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+ You should have received a copy of the GNU Lesser General Public
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+ License along with the GNU C Library. If not, see
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+ <http://www.gnu.org/licenses/>. */
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+
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+/* Number of extra dynamic section entries for this architecture. By
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+ default there are none. */
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+#define DT_THISPROCNUM DT_AARCH64_NUM
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diff --git a/sysdeps/aarch64/dl-machine.h b/sysdeps/aarch64/dl-machine.h
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index 4935aa7c543876db..d4494852b32b8783 100644
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--- a/sysdeps/aarch64/dl-machine.h
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+++ b/sysdeps/aarch64/dl-machine.h
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@@ -27,6 +27,9 @@
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#include <dl-irel.h>
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#include <cpu-features.c>
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+/* Translate a processor specific dynamic tag to the index in l_info array. */
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+#define DT_AARCH64(x) (DT_AARCH64_##x - DT_LOPROC + DT_NUM)
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+
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/* Return nonzero iff ELF header is compatible with the running host. */
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static inline int __attribute__ ((unused))
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elf_machine_matches_host (const ElfW(Ehdr) *ehdr)
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@@ -102,6 +105,10 @@ elf_machine_runtime_setup (struct link_map *l, int lazy, int profile)
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}
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}
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+ /* Check if STO_AARCH64_VARIANT_PCS needs to be handled. */
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+ if (l->l_info[DT_AARCH64 (VARIANT_PCS)])
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+ l->l_mach.variant_pcs = 1;
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+
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return lazy;
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}
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@@ -388,10 +395,37 @@ elf_machine_lazy_rel (struct link_map *map,
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/* Check for unexpected PLT reloc type. */
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if (__builtin_expect (r_type == AARCH64_R(JUMP_SLOT), 1))
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{
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- if (__builtin_expect (map->l_mach.plt, 0) == 0)
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- *reloc_addr += l_addr;
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- else
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- *reloc_addr = map->l_mach.plt;
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+ if (map->l_mach.plt == 0)
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+ {
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+ /* Prelinking. */
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+ *reloc_addr += l_addr;
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+ return;
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+ }
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+
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+ if (__glibc_unlikely (map->l_mach.variant_pcs))
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+ {
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+ /* Check the symbol table for variant PCS symbols. */
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+ const Elf_Symndx symndx = ELFW (R_SYM) (reloc->r_info);
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+ const ElfW (Sym) *symtab =
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+ (const void *)D_PTR (map, l_info[DT_SYMTAB]);
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+ const ElfW (Sym) *sym = &symtab[symndx];
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+ if (__glibc_unlikely (sym->st_other & STO_AARCH64_VARIANT_PCS))
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+ {
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+ /* Avoid lazy resolution of variant PCS symbols. */
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+ const struct r_found_version *version = NULL;
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+ if (map->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
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+ {
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+ const ElfW (Half) *vernum =
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+ (const void *)D_PTR (map, l_info[VERSYMIDX (DT_VERSYM)]);
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+ version = &map->l_versions[vernum[symndx] & 0x7fff];
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+ }
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+ elf_machine_rela (map, reloc, sym, version, reloc_addr,
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+ skip_ifunc);
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+ return;
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+ }
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+ }
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+
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+ *reloc_addr = map->l_mach.plt;
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}
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else if (__builtin_expect (r_type == AARCH64_R(TLSDESC), 1))
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{
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diff --git a/sysdeps/aarch64/linkmap.h b/sysdeps/aarch64/linkmap.h
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index 6852f343a1efd150..dd8597470c3d2174 100644
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--- a/sysdeps/aarch64/linkmap.h
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+++ b/sysdeps/aarch64/linkmap.h
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@@ -20,4 +20,5 @@ struct link_map_machine
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{
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ElfW(Addr) plt; /* Address of .plt */
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void *tlsdesc_table; /* Address of TLS descriptor hash table. */
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+ int variant_pcs; /* If set, PLT calls may follow a variant PCS. */
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};
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