Hi Alan,
On Tue, Nov 13, 2018 at 11:23:43PM +1030, Alan Modra wrote:
> Finally, the point of the previous patches in this series, support for
> inline PLT calls, keyed off -fno-plt. This emits code using new
> relocations that tie all insns in the sequence together, so that the
> linker can edit the sequence back to a direct call should the call
> target turn out to be local. An example of ELFv2 code to call puts is
> as follows:
>
> .reloc .,R_PPC64_PLTSEQ,puts
> std 2,24(1)
> .reloc .,R_PPC64_PLT16_HA,puts
> addis 12,2,0
> .reloc .,R_PPC64_PLT16_LO_DS,puts
> ld 12,0(12)
> .reloc .,R_PPC64_PLTSEQ,puts
> mtctr 12
> .reloc .,R_PPC64_PLTCALL,puts
> bctrl
> ld 2,24(1)
>
> "addis 12,2,puts@plt@ha" and "ld 12,puts@plt@l(12)" are also supported
> by the assembler. gcc instead uses the explicit R_PPC64_PLT16_HA and
> R_PPC64_PLT16_LO_DS relocs because when the call is to __tls_get_addr
> an extra reloc is emitted at every place where one is shown above, to
> specify the __tls_get_addr arg. The linker expects the extra reloc to
> come first. .reloc enforces that ordering.
>
> The patch also changes code emitted for longcalls if the assembler
> supports the new marker relocs, so that these too can be edited. One
> side effect of longcalls using PLT16 relocs is that they can now be
> resolved lazily by ld.so.
>
> I don't support lazy inline PLT calls for ELFv1, because ELFv1 would
> need barriers to reliably load both the function address and toc
> pointer from the PLT. ELFv1 -fno-plt uses the longcall sequence
> instead, which isn't edited by GNU ld.
That all sounds great :-) Has this been tested with older binutils, too?
> * config.in (HAVE_AS_PLTSEQ): Add.
> * config/rs6000/predicates.md (indirect_call_operand): New.
> * config/rs6000/rs6000-protos.h (rs6000_pltseq_template),
> (rs6000_sibcall_sysv): Declare.
> * config/rs6000/rs6000.c (init_cumulative_args): Set cookie
> CALL_LONG for -fno-plt.
> (print_operand <T, z, 0>): Handle UNSPEC_PLTSEQ.
> (rs6000_indirect_call_template_1): Emit .reloc directives for
> UNSPEC_PLTSEQ calls.
> (rs6000_pltseq_template): New function.
> (rs6000_longcall_ref): Add arg parameter. Use PLT16 insns if
> relocs supported by assembler. Move SYMBOL_REF test to callers.
> (rs6000_call_aix): Adjust rs6000_longcall_ref call. Package
> insns in UNSPEC_PLTSEQ, preserving original func_desc.
> (rs6000_call_sysv): Likewise.
> (rs6000_sibcall_sysv): New function.
> * config/rs6000/rs6000.h (HAVE_AS_PLTSEQ): Provide default.
> * config/rs6000/rs6000.md (UNSPEC_PLTSEQ, UNSPEC_PLT16_HA,
> UNSPEC_PLT16_LO): New.
> (pltseq_tocsave, pltseq_plt16_ha, pltseq_plt16_lo, pltseq_mtctr): New.
> (call_indirect_nonlocal_sysv): Don't differentiate zero from non-zero
> cookie in constraints. Test explicitly for flags in length attr.
> Handle unspec operand 1.
> (call_value_indirect_nonlocal_sysv): Likewise.
> (call_indirect_aix, call_value_indirect_aix): Handle unspec operand 1.
> (call_indirect_elfv2, call_value_indirect_elfv2): Likewise.
> (sibcall, sibcall_value): Use rs6000_sibcall_sysv.
> (sibcall_indirect_nonlocal_sysv): New pattern.
> (sibcall_value_indirect_nonlocal_sysv): Likewise.
> (sibcall_nonlocal_sysv, sibcall_value_nonlocal_sysv): Remove indirect
> call alternatives.
> * configure.ac: Check for gas plt sequence marker support.
> * configure: Regenerate.
> @@ -10727,10 +10727,20 @@ init_cumulative_args (CUMULATIVE_ARGS *cum, tree
> fntype,
> cum->nargs_prototype = n_named_args;
>
> /* Check for a longcall attribute. */
> - if ((!fntype && rs6000_default_long_calls)
> - || (fntype
> - && lookup_attribute ("longcall", TYPE_ATTRIBUTES (fntype))
> - && !lookup_attribute ("shortcall", TYPE_ATTRIBUTES (fntype))))
> + if (((!fntype && rs6000_default_long_calls)
> + || (fntype
> + && lookup_attribute ("longcall", TYPE_ATTRIBUTES (fntype))
> + && !lookup_attribute ("shortcall", TYPE_ATTRIBUTES (fntype))))
> + || (DEFAULT_ABI != ABI_DARWIN
> + && !(fndecl
> + && !DECL_EXTERNAL (fndecl)
> + && !DECL_WEAK (fndecl)
> + && (*targetm.binds_local_p) (fndecl))
> + && (flag_plt
> + ? (fntype
> + && lookup_attribute ("noplt", TYPE_ATTRIBUTES (fntype)))
> + : !(fntype
> + && lookup_attribute ("plt", TYPE_ATTRIBUTES (fntype))))))
> cum->call_cookie |= CALL_LONG;
Could you split this into a few cases? Maybe with some extra locals. It
is hard to understand the code as it is.
I mean like
if (...)
cum->call_cookie |= CALL_LONG;
if (...)
cum->call_cookie |= CALL_LONG;
if (...)
cum->call_cookie |= CALL_LONG;
> +(define_insn "*sibcall_indirect_nonlocal_sysv<mode>"
> + (set (attr "length")
> + (cond [(and (and (match_test "!rs6000_speculate_indirect_jumps")
> + (match_test "which_alternative != 1"))
> + (match_test "(INTVAL (operands[2]) & (CALL_V4_SET_FP_ARGS |
> CALL_V4_CLEAR_FP_ARGS))"))
> + (const_string "12")
> + (ior (and (match_test "!rs6000_speculate_indirect_jumps")
> + (match_test "which_alternative != 1"))
> + (match_test "(INTVAL (operands[2]) & (CALL_V4_SET_FP_ARGS |
> CALL_V4_CLEAR_FP_ARGS))"))
> + (const_string "8")]
> + (const_string "4")))])
Please use set_attr_alternative for these.
Looks fine modulo those nits. Okay for trunk. Thanks!
Segher
