In addition to the existing relocs we need two more to mark all
instructions in the call sequence, PLTCALL on the call itself (plus
the toc restore insn for ppc64), and PLTSEQ on others. All
relocations in a particular sequence have the same symbol.
Example ppc64 ELFv2 assembly:
.reloc .,R_PPC64_PLTSEQ,puts
std 2,24(1)
addis 12,2,puts@plt@ha # .reloc .,R_PPC64_PLT16_HA,puts
ld 12,puts@plt@l(12) # .reloc .,R_PPC64_PLT16_LO_DS,puts
.reloc .,R_PPC64_PLTSEQ,puts
mtctr 12
.reloc .,R_PPC64_PLTCALL,puts
bctrl
ld 2,24(1)
Example ppc32 -fPIC assembly:
addis 12,30,puts+32768@plt@ha # .reloc .,R_PPC_PLT16_HA,puts+0x8000
lwz 12,12,puts+32768@plt@l # .reloc .,R_PPC_PLT16_LO,puts+0x8000
.reloc .,R_PPC_PLTSEQ,puts+32768
mtctr 12
.reloc .,R_PPC_PLTCALL,puts+32768
bctrl
Marking sequences like this allows the linker to convert them to nops
and a direct call if the target symbol turns out to be local.
When the call is __tls_get_addr, each relocation shown above is paired
with an R_PPC*_TLSLD or R_PPC*_TLSGD reloc to additionally mark the
sequence for possible TLS optimization. The TLSLD or TLSGD relocs are
emitted first.
include/
* elf/ppc.h (R_PPC_PLTSEQ, R_PPC_PLTCALL): Define.
* elf/ppc64.h (R_PPC64_PLTSEQ, R_PPC64_PLTCALL): Define.
bfd/
* elf32-ppc.c (ppc_elf_howto_raw): Add PLTSEQ and PLTCALL howtos.
(is_plt_seq_reloc): New function.
(ppc_elf_check_relocs): Handle PLTSEQ and PLTCALL relocs.
(ppc_elf_tls_optimize): Handle inline plt call sequence.
(ppc_elf_relax_section): Handle PLTCALL reloc.
(ppc_elf_relocate_section): Nop out inline plt call sequence when
resolving locally.
* elf64-ppc.c (ppc64_elf_howto_raw): Add R_PPC64_PLTSEQ and
R_PPC64_PLTCALL entries. Comment R_PPC64_TOCSAVE.
(has_tls_get_addr_call): Correct comment.
(is_branch_reloc): Add PLTCALL.
(is_plt_seq_reloc): New function.
(ppc64_elf_check_relocs): Handle PLT16_LO_DS reloc. Set
has_tls_reloc for R_PPC64_TLSGD and R_PPC64_TLSLD. Create plt
entry for R_PPC64_PLTCALL.
(ppc64_elf_tls_optimize): Handle inline plt call sequence.
(ppc_type_of_stub): Handle PLTCALL reloc.
(toc_adjusting_stub_needed): Likewise.
(ppc64_elf_relocate_section): Set "can_plt_call" for PLTCALL
reloc insn. Nop out inline plt call sequence when resolving
locally. Handle __tls_get_addr inline plt call optimization.
elfcpp/
* powerpc.h (R_POWERPC_PLTSEQ, R_POWERPC_PLTCALL): Define.
gold/
* powerpc.cc (Target_powerpc::Track_tls::maybe_skip_tls_get_addr_call):
Handle inline plt sequence relocs.
(Stub_table::Plt_stub_key::Plt_stub_key): Likewise.
(Target_powerpc::Scan::reloc_needs_plt_for_ifunc): Likewise.
(Target_powerpc::Relocate::relocate): Likewise.
This implements the special __tls_get_addr_opt call stub for powerpc
gold that returns __thread variable addresses without actually making
a call to __tls_get_addr in most cases. Shared libraries that are
loaded at program load time (ie. dlopen is not used) have a known
layout for their __thread variables, and thus DTPMOD64/DPTREL64 pairs
describing those variables can be set up by ld.so for the
__tls_get_addr_opt call stub fast exit.
Ref https://sourceware.org/ml/libc-alpha/2015-03/msg00626.html
I really, really wish I'd used a differently versioned __tls_get_addr
symbol than the base symbol to indicate glibc support for the
optimized call, rather than having glibc export __tls_get_addr_opt. A
lot of the messing around here, flipping symbols from __tls_get_addr
to __tls_get_addr_opt, is caused by that decision. About the only
benefit is that a user can see at a glance that their disassembled
code is calling __tls_get_addr via the fancy call stub.. Anyway, we
need references to __tls_get_addr to seem like they were to
__tls_get_addr_opt, and in cases like the tsan interceptor, a
definition of __tls_get_addr to seem like one of __tls_get_addr_opt
as well. That's the reason for Symbol::clear_in_reg and
Symbol_table::clone, and why symbols are substituted in Scan::global
and other places dealing with dynamic linking.
elfcpp/
* elfcpp.h (DT_PPC_OPT): Define.
* powerpc.h (PPC_OPT_TLS): Define.
gold/
* options.h (tls_get_addr_optimize): New option.
* symtab.h (Symbol::clear_in_reg, clone): New functions.
(Sized_symbol::clone): New function.
(Symbol_table::clone): New function.
* resolve.cc (Symbol::clone, Sized_symbol::clone): New functions.
* powerpc.cc (Target_powerpc::has_tls_get_addr_opt_,
tls_get_addr_, tls_get_addr_opt_): New vars.
(Target_powerpc::tls_get_addr_opt, tls_get_addr,
is_tls_get_addr_opt, replace_tls_get_addr,
set_has_tls_get_addr_opt, stk_linker): New functions.
(Target_powerpc::Track_tls::maybe_skip_tls_get_addr_call): Add
target param. Update callers. Compare symbols rather than names.
(Target_powerpc::do_define_standard_symbols): Init tls_get_addr_
and tls_get_addr_opt_.
(Target_powerpc::Branch_info::mark_pltcall): Translate tls_get_addr
sym to tls_get_addr_opt.
(Target_powerpc::Branch_info::make_stub): Likewise.
(Stub_table::define_stub_syms): Likewise.
(Target_powerpc::Scan::global): Likewise.
(Target_powerpc::Relocate::relocate): Likewise.
(add_3_12_2, add_3_12_13, bctrl, beqlr, cmpdi_11_0, cmpwi_11_0,
ld_11_1, ld_11_3, ld_12_3, lwz_11_3, lwz_12_3, mr_0_3, mr_3_0,
mtlr_11, std_11_1): New constants.
(Stub_table::eh_frame_added_): Delete.
(Stub_table::tls_get_addr_opt_bctrl_, plt_fde_len_, plt_fde_): New vars.
(Stub_table::init_plt_fde): New functions.
(Stub_table::add_eh_frame, replace_eh_frame): Move definition out
of line. Init and use plt_fde_.
(Stub_table::plt_call_size): Return size for tls_get_addr stub.
Extract alignment code to..
(Stub_table::plt_call_align): ..this new function. Adjust all callers.
(Stub_table::add_plt_call_entry): Set has_tls_get_addr_opt and
tls_get_addr_opt_bctrl, and align after that.
(Stub_table::do_write): Write out tls_get_addr stub.
(Target_powerpc::do_finalize_sections): Emit DT_PPC_OPT
PPC_OPT_TLS/PPC64_OPT_TLS bit.
(Target_powerpc::Relocate::relocate): Don't check for or modify
nop following bl for tls_get_addr stub.
elfcpp/
* elfcpp.h (DT_PPC64_OPT): Define.
* powerpc.h (PPC64_OPT_TLS, PPC64_OPT_MULTI_TOC,
PPC64_OPT_LOCALENTRY): Define.
gold/
* options.h (General_options): Add plt_localentry.
* powerpc.cc (Target_powerpc::st_other): New function.
(Target_powerpc::plt_localentry0_, plt_localentry0_init_,
has_localentry0_): New vars.
(Target_powerpc::plt_localentry0, set_has_localentry0,
is_elfv2_localentry0): New functions.
(Target_powerpc::Branch_info::mark_pltcall): Don't set tocsave or
return true for localentry:0 calls.
(Stub_table::Plt_stub_ent::localentry0_): New var.
(Stub_table::add_plt_call_entry): Set localentry0_ and has_localentry0_.
Don't set r2save_ for localentry:0 calls.
(Output_data_glink::do_write): Save r2 in __glink_PLTresolve for elfv2.
(Target_powerpc::scan_relocs): Default plt_localentry0_.
(Target_powerpc::do_finalize_sections): Set DT_PPC64_OPT.
(Target_powerpc::Relocate::relocate): Don't require nop following
calls for localentry:0 plt calls, and don't change nop.
This adds support for "func@localentry", an expression that returns the
ELFv2 local entry point address of function "func". I've excluded
dynamic relocation support because that obviously would require glibc
changes.
include/elf/
* ppc64.h (R_PPC64_REL24_NOTOC, R_PPC64_ADDR64_LOCAL): Define.
bfd/
* elf64-ppc.c (ppc64_elf_howto_raw): Add R_PPC64_ADDR64_LOCAL entry.
(ppc64_elf_reloc_type_lookup): Support R_PPC64_ADDR64_LOCAL.
(ppc64_elf_check_relocs): Likewise.
(ppc64_elf_relocate_section): Likewise.
* Add BFD_RELOC_PPC64_ADDR64_LOCAL.
* bfd-in2.h: Regenerate.
* libbfd.h: Regenerate.
gas/
* config/tc-ppc.c (ppc_elf_suffix): Support @localentry.
(md_apply_fix): Support R_PPC64_ADDR64_LOCAL.
ld/testsuite/
* ld-powerpc/elfv2-2a.s, ld-powerpc/elfv2-2b.s: New files.
* ld-powerpc/elfv2-2exe.d, ld-powerpc/elfv2-2so.d: New files.
* ld-powerpc/powerpc.exp: Run new test.
elfcpp/
* powerpc.h (R_PPC64_REL24_NOTOC, R_PPC64_ADDR64_LOCAL): Define.
gold/
* powerpc.cc (Target_powerpc::Scan::local, global): Support
R_PPC64_ADDR64_LOCAL.
(Target_powerpc::Relocate::relocate): Likewise.
elfcpp/
* powerpc.h (EF_PPC64_ABI): New enum constant.
(STO_PPC64_LOCAL_BIT, STO_PPC64_LOCAL_MASK): Likewise.
(ppc64_decode_local_entry): New function.
(ppc64_encode_local_entry): Likewise.
gold/
* powerpc.cc (Powerpc_relobj::abiversion, set_abiversion,
ppc64_local_entry_offset, ppc64_local_entry_offset,
do_read_symbols): New functions.
(Powerpc_relobj::e_flags_, st_other_): New vars.
(Powerpc_relobj::Powerpc_relobj): Call set_abiversion.
(Powerpc_dynobj::abiversion, set_abiversion): New functions.
(Powerpc_relobj::e_flags_): New var.
(Target_powerpc::first_plt_entry_offset, plt_entry_size): Inline
and adjust for ELFv2.
(Target_powerpc::abiversion, set_abiversion, stk_toc): New functions.
(Powerpc_relobj::do_find_special_sections): Check no .opd in ELFv2.
(Powerpc_dynobj::do_find_special_sections): Likewise.
(Target_powerpc::do_define_standard_symbols): Define ".TOC.".
(Target_powerpc::Branch_info::make_stub): Adjust stub destination
to ELFv2 local entry.
(Target_powerpc::do_relax): No thread safe barriers needed for
ELFv2.
(Output_data_plt_powerpc::initial_plt_entry_size_,
plt_entry_size): Delete. Replace all uses with
first_plt_entry_offset() and plt_entry_size().
(Output_data_plt_powerpc::Output_data_plt_powerpc): Remove
reserved_size parm. Update callers.
(Output_data_plt_powerpc::entry_count): Update.
(Output_data_plt_powerpc::first_plt_entry_offset): Make private
and use Target_powerpc::first_plt_entry_offset().
(Output_data_plt_powerpc::get_plt_entry_size): Similarly and
rename to plt_entry_size.
(Output_data_plt_powerpc::add_ifunc_entry,
add_local_ifunc_entry): Adjust reloc for ELFv2.
(glink_eh_frame_fde_64): Rename to glink_eh_frame_fde_64v1.
(glink_eh_frame_fde_64v2): New.
(Stub_table::plt_call_size): Support ELFv2 sizing.
(Output_data_glink::add_eh_frame): Use the new FDE.
(Output_data_glink::set_final_data_size): Adjust for ELFv2 glink.
(Stub_table::do_write): Write ELFv2 stubs and glink.
(Target_powerpc::Relocate::relocate): Replaces nop after call
with ld 2,24(1) and adjust local offset destination for ELFv2.
This changes the behaviour of @h and @ha on PowerPC64 to report errors
on 32-bit overflow. The motivation for this change is that on
PowerPC64, most uses of @h and @ha modifiers and their corresponding
relocations are to build up 32-bit offsets. We'd like to know when
such offsets overflow. Only rarely do people use @h or @ha with the
high 32-bit modifiers to build a 64-bit constant. Those uses will now
need to use two new modifiers, @high and @higha, if the constant isn't
known at assembly time. For now, we won't report overflow at assembly
time..
This also fixes an error when applying some of the HIGHER and HIGHEST
relocations.
include/elf/
* ppc64.h (R_PPC64_ADDR16_HIGH, R_PPC64_ADDR16_HIGHA,
R_PPC64_TPREL16_HIGH, R_PPC64_TPREL16_HIGHA,
R_PPC64_DTPREL16_HIGH, R_PPC64_DTPREL16_HIGHA): New.
(IS_PPC64_TLS_RELOC): Match new tls relocs.
bfd/
* reloc.c (BFD_RELOC_PPC64_ADDR16_HIGH, BFD_RELOC_PPC64_ADDR16_HIGHA,
BFD_RELOC_PPC64_TPREL16_HIGH, BFD_RELOC_PPC64_TPREL16_HIGHA,
BFD_RELOC_PPC64_DTPREL16_HIGH, BFD_RELOC_PPC64_DTPREL16_HIGHA): New.
* elf64-ppc.c (ppc64_elf_howto_raw): Add entries for new relocs.
Make all _HA and _HI relocs report signed overflow.
(ppc64_elf_reloc_type_lookup): Handle new relocs.
(must_be_dyn_reloc, ppc64_elf_check_relocs): Likewise.
(dec_dynrel_count, ppc64_elf_relocate_section): Likewise.
(ppc64_elf_relocate_section): Don't apply 0x8000 adjust to
R_PPC64_TPREL16_HIGHER, R_PPC64_TPREL16_HIGHEST,
R_PPC64_DTPREL16_HIGHER, and R_PPC64_DTPREL16_HIGHEST.
* libbfd.h: Regenerate.
* bfd-in2.h: Regenerate.
gas/
* config/tc-ppc.c (SEX16): Don't mask.
(REPORT_OVERFLOW_HI): Define as zero.
(ppc_elf_suffix): Support @high, @higha, @dtprel@high, @dtprel@higha,
@tprel@high, and @tprel@higha modifiers.
(md_assemble): Ignore X_unsigned when applying 16-bit insn fields.
Add (disabled) code to check @h and @ha reloc overflow for powerpc64.
Handle new relocs.
(md_apply_fix): Similarly.
elfcpp/
* powerpc.h (R_PPC64_ADDR16_HIGH, R_PPC64_ADDR16_HIGHA,
R_PPC64_TPREL16_HIGH, R_PPC64_TPREL16_HIGHA,
R_PPC64_DTPREL16_HIGH, R_PPC64_DTPREL16_HIGHA): Define.
gold/
* powerpc.cc (Target_powerpc::Scan::check_non_pic): Handle new relocs.
(Target_powerpc::Scan::global, local): Likewise.
(Target_powerpc::Relocate::relocate): Likewise. Check for overflow
on all ppc64 @h and @ha relocs.
* powerpc.h: Add more relocs.
(R_PPC_REL16*): Rename to R_POWERPC_REL16*.
gold/
* powerpc.cc: Update for renamed R_PPC_REL16 relocs.
(Output_data_got_powerpc::do_write): Don't rely on base class lookup
for replace_constant call.
(Output_data_plt_powerpc::do_print_to_mapfile): New function.
(Output_data_glink::do_print_to_mapfile): New function.
(Target_powerpc::Scan::local): Ignore R_PPC64_TOCSAVE.
(Target_powerpc::Relocate::relocate): Likewise.
