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[BZ #18572] arm: Disable lazy initialization of tlsdesc entries

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Follow up to
https://sourceware.org/ml/libc-alpha/2015-11/msg00272.html

Always do tls descriptor initialization at load time during relocation
processing (as if DF_BIND_NOW were set for the binary) to avoid barriers
at every tls access.  This patch mimics bind-now semantics in the lazy
relocation code of the arm target (elf_machine_lazy_rel).

Ideally the static linker should be updated too to not emit tlsdesc
relocs in DT_REL*, so elf_machine_lazy_rel is not called on them at all.

	[BZ #18572]
	* sysdeps/arm/dl-machine.h (elf_machine_lazy_rel): Do symbol binding
	non-lazily for R_ARM_TLS_DESC.
This commit is contained in:
Szabolcs Nagy 2017-10-20 17:35:12 +01:00
parent 2c1d4e5fe4
commit 0ca3d1d6d0
2 changed files with 20 additions and 8 deletions
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ChangeLog
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@ -1,3 +1,9 @@
2017-11-03 Szabolcs Nagy <szabolcs.nagy@arm.com>
[BZ #18572]
* sysdeps/arm/dl-machine.h (elf_machine_lazy_rel): Do symbol binding
non-lazily for R_ARM_TLS_DESC.
2017-11-03 Szabolcs Nagy <szabolcs.nagy@arm.com>
[BZ #17078]

22
sysdeps/arm/dl-machine.h
View File

@ -669,15 +669,21 @@ elf_machine_lazy_rel (struct link_map *map,
}
else if (__builtin_expect (r_type == R_ARM_TLS_DESC, 1))
{
struct tlsdesc volatile *td =
(struct tlsdesc volatile *)reloc_addr;
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];
const struct r_found_version *version = NULL;
/* The linker must have given us the parameter we need in the
first GOT entry, and left the second one empty. We fill the
latter with the resolver address. */
assert (td->entry == 0);
td->entry = (void*)(D_PTR (map, l_info[ADDRIDX (DT_TLSDESC_PLT)])
+ map->l_addr);
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];
}
/* Always initialize TLS descriptors completely, because lazy
initialization requires synchronization at every TLS access. */
elf_machine_rel (map, reloc, sym, version, reloc_addr, skip_ifunc);
}
else
_dl_reloc_bad_type (map, r_type, 1);