PowerPC PLT speculative execution barriers

Spectre variant 2 mitigation for PowerPC and PowerPC64.

bfd/
	* elf32-ppc.c (GLINK_ENTRY_SIZE): Handle speculation barrier.
	(CRSETEQ, BEQCTRM): Define.
	(is_nonpic_glink_stub): Don't check bctr.
	(ppc_elf_link_hash_table_create): Init new ppc_elf_params field.
	(ppc_elf_relax_section): Size speculation barrier.
	(output_bctr): New function.
	(write_glink_stub): Use output_bctr.
	(ppc_elf_relocate_section): Use output_bctr for long branch stub.
	(ppc_elf_finish_dynamic_symbol): Likewise.
	(ppc_elf_finish_dynamic_sections): Use output_bctr.
	* elf32-ppc.h (struct ppc_elf_params): Add speculate_indirect_jumps.
	* elf64-ppc.c (CRSETEQ, BEQCTRM, BEQCTRLM): Define.
	(GLINK_PLTRESOLVE_SIZE): Size speculation barrier.
	(size_global_entry_stubs): Handle speculation barrier sizing.
	(plt_stub_size): Likewise.
	(output_bctr): New function.
	(build_plt_stub, build_tls_get_addr_stub): Output speculation
	barrier.
	(ppc_build_one_stub): Likewise for ppc_stub_plt_branch.
	(ppc_size_one_stub): Size speculation barrier in ppc_stub_plt_branch.
	(build_global_entry_stubs): Output speculation barrier.
	(ppc64_elf_build_stubs): Likewise in __glink_PLTresolve stub.
	* elf64-ppc.h (struct ppc64_elf_params): Add speculate_indirect_jumps.
gold/
	* options.h (speculate_indirect_jumps): New option.
	* powerpc.cc (beqctrm, beqctrlm, crseteq): New insn constants.
	(output_bctr): New function.
	(Stub_table::plt_call_size): Add space for speculation barrier.
	(Stub_table::branch_stub_size): Likewise.
	(Output_data_glink::pltresolve_size): Likewise.
	(Stub_table::do_write): Output speculation barriers.
ld/
	* emultempl/ppc32elf.em (params): Init new field.
	(OPTION_SPECULATE_INDIRECT_JUMPS): Define.
	(OPTION_NO_SPECULATE_INDIRECT_JUMPS): Define.
	(PARSE_AND_LIST_LONGOPTS): Handle new options.
	(PARSE_AND_LIST_ARGS_CASES): Likewise.
	(PARSE_AND_LIST_OPTIONS): Likewise.
	* emultempl/ppc64elf.em (params): Init new field.
	(OPTION_SPECULATE_INDIRECT_JUMPS): Define.
	(OPTION_NO_SPECULATE_INDIRECT_JUMPS): Define.
	(PARSE_AND_LIST_LONGOPTS): Handle --speculate-indirect-jumps.
	(PARSE_AND_LIST_OPTIONS): Likewise.
	(PARSE_AND_LIST_ARGS_CASES): Likewise.
	* ld.texinfo (--no-plt-thread-safe): Correct itemx.
	(--speculate-indirect-jumps): Document.
	* testsuite/ld-powerpc/elfv2exe.d,
	* testsuite/ld-powerpc/elfv2so.d,
	* testsuite/ld-powerpc/relbrlt.d,
	* testsuite/ld-powerpc/powerpc.exp: Disable plt alignment and
	speculation barriers on various tests.

1 files changed, 10 insertions, 1 deletions

diff --git a/ld/ld.texinfo b/ld/ld.texinfo
index 94d340c..c89915f 100644
--- a/ld/ld.texinfo
+++ b/ld/ld.texinfo
@@ -7635,7 +7635,7 @@ chain since there is never any need to do so on a PLT call.
 @kindex --plt-thread-safe
 @kindex --no-plt-thread-safe
 @item --plt-thread-safe
-@itemx --no-thread-safe
+@itemx --no-plt-thread-safe
 With power7's weakly ordered memory model, it is possible when using
 lazy binding for ld.so to update a plt entry in one thread and have
 another thread see the individual plt entry words update in the wrong
@@ -7646,6 +7646,15 @@ looks for calls to commonly used functions that create threads, and if
 seen, adds the necessary barriers.  Use these options to change the
 default behaviour.
 
+@cindex PowerPC64 PLT call stub speculative execution barrier
+@kindex --speculate-indirect-jumps
+@kindex --no-speculate-indirect-jumps
+@item --speculate-indirect-jumps
+@itemx --no-speculate-indirect-jumps
+Use these options to control whether all indirect branch instructions
+emitted by @code{ld}, such as those in the PLT, have a speculative
+execution barrier to mitigate Spectre variant 2 attacks.
+
 @cindex PowerPC64 ELFv2 PLT localentry optimization
 @kindex --plt-localentry
 @kindex --no-plt-localentry