aboutsummaryrefslogtreecommitdiffstats
diff options
context:
space:
mode:
authorSzabolcs Nagy <szabolcs.nagy@arm.com>2019-04-25 15:35:35 +0100
committerSzabolcs Nagy <szabolcs.nagy@arm.com>2019-06-13 09:45:00 +0100
commit82bc69c012838a381c4167c156a06f4598f34227 (patch)
treebc144470174a699d006b4bfb171b859e9ba49488
parent55f82d328d2dd1c7c13c1992f4b9bf9c95b57551 (diff)
downloadglibc-82bc69c012838a381c4167c156a06f4598f34227.tar.gz
glibc-82bc69c012838a381c4167c156a06f4598f34227.tar.xz
glibc-82bc69c012838a381c4167c156a06f4598f34227.zip
aarch64: handle STO_AARCH64_VARIANT_PCS
Avoid lazy binding of symbols that may follow a variant PCS with different register usage convention from the base PCS. Currently the lazy binding entry code does not preserve all the registers required for AdvSIMD and SVE vector calls. Saving and restoring all registers unconditionally may break existing binaries, even if they never use vector calls, because of the larger stack requirement for lazy resolution, which can be significant on an SVE system. The solution is to mark all symbols in the symbol table that may follow a variant PCS so the dynamic linker can handle them specially. In this patch such symbols are always resolved at load time, not lazily. So currently LD_AUDIT for variant PCS symbols are not supported, for that the _dl_runtime_profile entry needs to be changed e.g. to unconditionally save/restore all registers (but pass down arg and retval registers to pltentry/exit callbacks according to the base PCS). This patch also removes a __builtin_expect from the modified code because the branch prediction hint did not seem useful. * sysdeps/aarch64/dl-dtprocnum.h: New file. * sysdeps/aarch64/dl-machine.h (DT_AARCH64): Define. (elf_machine_runtime_setup): Handle DT_AARCH64_VARIANT_PCS. (elf_machine_lazy_rel): Check STO_AARCH64_VARIANT_PCS and bind such symbols at load time. * sysdeps/aarch64/linkmap.h (struct link_map_machine): Add variant_pcs.
-rw-r--r--ChangeLog9
-rw-r--r--sysdeps/aarch64/dl-dtprocnum.h21
-rw-r--r--sysdeps/aarch64/dl-machine.h42
-rw-r--r--sysdeps/aarch64/linkmap.h1
4 files changed, 69 insertions, 4 deletions
diff --git a/ChangeLog b/ChangeLog
index 456b9ba8bbd..7cc8f6e8054 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,14 @@
2019-06-13 Szabolcs Nagy <szabolcs.nagy@arm.com>
+ * sysdeps/aarch64/dl-dtprocnum.h: New file.
+ * sysdeps/aarch64/dl-machine.h (DT_AARCH64): Define.
+ (elf_machine_runtime_setup): Handle DT_AARCH64_VARIANT_PCS.
+ (elf_machine_lazy_rel): Check STO_AARCH64_VARIANT_PCS and bind such
+ symbols at load time.
+ * sysdeps/aarch64/linkmap.h (struct link_map_machine): Add variant_pcs.
+
+2019-06-13 Szabolcs Nagy <szabolcs.nagy@arm.com>
+
* elf/elf.h (STO_AARCH64_VARIANT_PCS): Define.
(DT_AARCH64_VARIANT_PCS): Define.
diff --git a/sysdeps/aarch64/dl-dtprocnum.h b/sysdeps/aarch64/dl-dtprocnum.h
new file mode 100644
index 00000000000..4ac2adf2345
--- /dev/null
+++ b/sysdeps/aarch64/dl-dtprocnum.h
@@ -0,0 +1,21 @@
+/* Configuration of lookup functions. AArch64 version.
+ Copyright (C) 2019 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
+ <http://www.gnu.org/licenses/>. */
+
+/* Number of extra dynamic section entries for this architecture. By
+ default there are none. */
+#define DT_THISPROCNUM DT_AARCH64_NUM
diff --git a/sysdeps/aarch64/dl-machine.h b/sysdeps/aarch64/dl-machine.h
index 823eefba460..4f27637b201 100644
--- a/sysdeps/aarch64/dl-machine.h
+++ b/sysdeps/aarch64/dl-machine.h
@@ -27,6 +27,9 @@
#include <dl-irel.h>
#include <cpu-features.c>
+/* Translate a processor specific dynamic tag to the index in l_info array. */
+#define DT_AARCH64(x) (DT_AARCH64_##x - DT_LOPROC + DT_NUM)
+
/* Return nonzero iff ELF header is compatible with the running host. */
static inline int __attribute__ ((unused))
elf_machine_matches_host (const ElfW(Ehdr) *ehdr)
@@ -102,6 +105,10 @@ elf_machine_runtime_setup (struct link_map *l, int lazy, int profile)
}
}
+ /* Check if STO_AARCH64_VARIANT_PCS needs to be handled. */
+ if (l->l_info[DT_AARCH64 (VARIANT_PCS)])
+ l->l_mach.variant_pcs = 1;
+
return lazy;
}
@@ -388,10 +395,37 @@ elf_machine_lazy_rel (struct link_map *map,
/* Check for unexpected PLT reloc type. */
if (__builtin_expect (r_type == AARCH64_R(JUMP_SLOT), 1))
{
- if (__builtin_expect (map->l_mach.plt, 0) == 0)
- *reloc_addr += l_addr;
- else
- *reloc_addr = map->l_mach.plt;
+ if (map->l_mach.plt == 0)
+ {
+ /* Prelinking. */
+ *reloc_addr += l_addr;
+ return;
+ }
+
+ if (__glibc_unlikely (map->l_mach.variant_pcs))
+ {
+ /* Check the symbol table for variant PCS symbols. */
+ const Elf_Symndx symndx = ELFW (R_SYM) (reloc->r_info);
+ const ElfW (Sym) *symtab =
+ (const void *)D_PTR (map, l_info[DT_SYMTAB]);
+ const ElfW (Sym) *sym = &symtab[symndx];
+ if (__glibc_unlikely (sym->st_other & STO_AARCH64_VARIANT_PCS))
+ {
+ /* Avoid lazy resolution of variant PCS symbols. */
+ const struct r_found_version *version = NULL;
+ if (map->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
+ {
+ const ElfW (Half) *vernum =
+ (const void *)D_PTR (map, l_info[VERSYMIDX (DT_VERSYM)]);
+ version = &map->l_versions[vernum[symndx] & 0x7fff];
+ }
+ elf_machine_rela (map, reloc, sym, version, reloc_addr,
+ skip_ifunc);
+ return;
+ }
+ }
+
+ *reloc_addr = map->l_mach.plt;
}
else if (__builtin_expect (r_type == AARCH64_R(TLSDESC), 1))
{
diff --git a/sysdeps/aarch64/linkmap.h b/sysdeps/aarch64/linkmap.h
index ba74fe10e12..7f801b14db2 100644
--- a/sysdeps/aarch64/linkmap.h
+++ b/sysdeps/aarch64/linkmap.h
@@ -20,4 +20,5 @@ struct link_map_machine
{
ElfW(Addr) plt; /* Address of .plt */
void *tlsdesc_table; /* Address of TLS descriptor hash table. */
+ int variant_pcs; /* If set, PLT calls may follow a variant PCS. */
};