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PowerPC64 thread-safe stubs not needed for iplt

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I was looking at a current glibc using objdump today and saw an odd
plt call stub.

0000000000044d80 <00000033.plt_call.__strchrnul>:
   44d80:       f8 41 00 28     std     r2,40(r1)
   44d84:       e9 82 8c f8     ld      r12,-29448(r2)
   44d88:       7d 89 03 a6     mtctr   r12
   44d8c:       e8 42 8d 00     ld      r2,-29440(r2)
   44d90:       28 22 00 00     cmpldi  r2,0
   44d94:       4c e2 04 20     bnectr+
   44d98:       48 13 84 f0     b       17d288 <realloc@plt>

What?  It doesn't branch to __strchrnul@plt on finding a zero r2?

Turns out this isn't a real problem since the stub is for loading an
ifunc, so will not be lazily resolved and thus r2 will never be zero.
Of course, that means the thread-safety check is unnecessary.

I also tweak the special __tls_get_addr_opt call stub here, to
restore r2 immediately after the call.  Not doing that might affect
eh_frame unwinding.

	* elf64-ppc.c (plt_stub_size, build_plt_stub): Don't build
	thread-safe stubs for iplt.
	(build_tls_get_addr_stub): Restore r2 immediately after call.
This commit is contained in:
Alan Modra
2015-02-26 21:26:42 +10:30
parent cf424aef0a
commit bd4d2eaad0
2 changed files with 17 additions and 6 deletions
Download Patch File Download Diff File Expand all files Collapse all files

6
bfd/ChangeLog
View File

@ -1,3 +1,9 @@
2015-02-26 Alan Modra <amodra@gmail.com>
* elf64-ppc.c (plt_stub_size, build_plt_stub): Don't build
thread-safe stubs for iplt.
(build_tls_get_addr_stub): Restore r2 immediately after call.
2015-02-26 Terry Guo <terry.guo@arm.com> 2015-02-26 Terry Guo <terry.guo@arm.com>
* elf32-arm.c (elf32_arm_merge_eabi_attributes): Update how we * elf32-arm.c (elf32_arm_merge_eabi_attributes): Update how we

17
bfd/elf64-ppc.c
View File

@ -10220,7 +10220,10 @@ plt_stub_size (struct ppc_link_hash_table *htab,
size += 4; size += 4;
if (htab->params->plt_static_chain) if (htab->params->plt_static_chain)
size += 4; size += 4;
if (htab->params->plt_thread_safe) if (htab->params->plt_thread_safe
&& htab->elf.dynamic_sections_created
&& stub_entry->h != NULL
&& stub_entry->h->elf.dynindx != -1)
size += 8; size += 8;
if (PPC_HA (off + 8 + 8 * htab->params->plt_static_chain) != PPC_HA (off)) if (PPC_HA (off + 8 + 8 * htab->params->plt_static_chain) != PPC_HA (off))
size += 4; size += 4;
@ -10260,16 +10263,18 @@ build_plt_stub (struct ppc_link_hash_table *htab,
bfd *obfd = htab->params->stub_bfd; bfd *obfd = htab->params->stub_bfd;
bfd_boolean plt_load_toc = htab->opd_abi; bfd_boolean plt_load_toc = htab->opd_abi;
bfd_boolean plt_static_chain = htab->params->plt_static_chain; bfd_boolean plt_static_chain = htab->params->plt_static_chain;
bfd_boolean plt_thread_safe = htab->params->plt_thread_safe; bfd_boolean plt_thread_safe = (htab->params->plt_thread_safe
&& htab->elf.dynamic_sections_created
&& stub_entry->h != NULL
&& stub_entry->h->elf.dynindx != -1);
bfd_boolean use_fake_dep = plt_thread_safe; bfd_boolean use_fake_dep = plt_thread_safe;
bfd_vma cmp_branch_off = 0; bfd_vma cmp_branch_off = 0;
if (!ALWAYS_USE_FAKE_DEP if (!ALWAYS_USE_FAKE_DEP
&& plt_load_toc && plt_load_toc
&& plt_thread_safe && plt_thread_safe
&& !(stub_entry->h != NULL && !((stub_entry->h == htab->tls_get_addr_fd
&& (stub_entry->h == htab->tls_get_addr_fd || stub_entry->h == htab->tls_get_addr)
|| stub_entry->h == htab->tls_get_addr)
&& !htab->params->no_tls_get_addr_opt)) && !htab->params->no_tls_get_addr_opt))
{ {
bfd_vma pltoff = stub_entry->plt_ent->plt.offset & ~1; bfd_vma pltoff = stub_entry->plt_ent->plt.offset & ~1;
@ -10462,8 +10467,8 @@ build_tls_get_addr_stub (struct ppc_link_hash_table *htab,
p = build_plt_stub (htab, stub_entry, p, offset, r); p = build_plt_stub (htab, stub_entry, p, offset, r);
bfd_put_32 (obfd, BCTRL, p - 4); bfd_put_32 (obfd, BCTRL, p - 4);
bfd_put_32 (obfd, LD_R11_0R1 + STK_LINKER (htab), p), p += 4;
bfd_put_32 (obfd, LD_R2_0R1 + STK_TOC (htab), p), p += 4; bfd_put_32 (obfd, LD_R2_0R1 + STK_TOC (htab), p), p += 4;
bfd_put_32 (obfd, LD_R11_0R1 + STK_LINKER (htab), p), p += 4;
bfd_put_32 (obfd, MTLR_R11, p), p += 4; bfd_put_32 (obfd, MTLR_R11, p), p += 4;
bfd_put_32 (obfd, BLR, p), p += 4; bfd_put_32 (obfd, BLR, p), p += 4;