[PATCH] RISC-V: Add --[no-]relax-gp to ld
Fangrui Song
maskray@google.com
Mon Feb 20 03:46:12 GMT 2023
On 2023-02-20, Nelson Chu wrote:
>This is just a target option, and it's not only for compatibility with
>lld, sometimes this option is also convenient to catch whether the gp
>relaxation has a bug without rebuilding the linker to disable the
>specific relaxation. Personally I would say this is a good idea at
>least for debugging, we just default enable the relax flags in the
>riscv_elf_params, so that everything won't change. Perhaps from the
>debug point of view, it may be the right direction to have other
>developer target options to close the remaining specific relaxations.
>Anyway, this target option works for me, it's not only good for
>developer debugging, but also keeps it compatible with lld. However,
>it would be better to just wait so as not to miss some of the other
>suggestions, I think 1-2 weeks should be enough.
>
>Thanks
>Nelson
Thank you for the feedback!
>On Sat, Feb 18, 2023 at 3:31 PM Fangrui Song <i@maskray.me> wrote:
>>
>> On Wed, Jul 13, 2022 at 1:26 AM Fangrui Song <maskray@google.com> wrote:
>> >
>> > From: Fangrui Song <i@maskray.me>
>> >
>> > --relax enables all relaxations. --no-relax-gp disables GP relaxation to
>> > allow measuring its effect.
>> >
>> > Link: https://github.com/riscv-non-isa/riscv-elf-psabi-doc/issues/298
>> >
>> > bfd/
>> > * elfnn-riscv.c (struct riscv_elf_link_hash_table): Add params.
>> > (riscv_elfNN_set_options): New.
>> > (riscv_info_to_howto_rela): Check relax_gp.
>> > (_bfd_riscv_relax_section): Likewise.
>> > * elfxx-riscv.h (struct riscv_elf_params): New.
>> > (riscv_elf32_set_options): New.
>> > (riscv_elf64_set_options): New.
>> > ld/
>> > * emultempl/riscvelf.em: Add option parsing.
>> > * testsuite/ld-riscv-elf/code-model-relax-medlow-01-norelaxgp.d: New.
>> > * testsuite/ld-riscv-elf/pcgp-relax-01-norelaxgp.d: New.
>> > * testsuite/ld-riscv-elf/pcgp-relax-02.d: Test --relax --relax-gp can be
>> > used together.
>> > ---
>> > bfd/elfnn-riscv.c | 22 ++++++++++---
>> > bfd/elfxx-riscv.h | 11 +++++++
>> > ld/emultempl/riscvelf.em | 31 +++++++++++++++++++
>> > .../code-model-relax-medlow-01-norelaxgp.d | 4 +++
>> > ld/testsuite/ld-riscv-elf/ld-riscv-elf.exp | 2 ++
>> > .../ld-riscv-elf/pcgp-relax-01-norelaxgp.d | 18 +++++++++++
>> > ld/testsuite/ld-riscv-elf/pcgp-relax-02.d | 2 +-
>> > 7 files changed, 84 insertions(+), 6 deletions(-)
>> > create mode 100644 ld/testsuite/ld-riscv-elf/code-model-relax-medlow-01-norelaxgp.d
>> > create mode 100644 ld/testsuite/ld-riscv-elf/pcgp-relax-01-norelaxgp.d
>> >
>> > diff --git a/bfd/elfnn-riscv.c b/bfd/elfnn-riscv.c
>> > index 8f9f0d8a86a..527c3e74e97 100644
>> > --- a/bfd/elfnn-riscv.c
>> > +++ b/bfd/elfnn-riscv.c
>> > @@ -118,6 +118,9 @@ struct riscv_elf_link_hash_table
>> > {
>> > struct elf_link_hash_table elf;
>> >
>> > + /* Various options and other info passed from the linker. */
>> > + struct riscv_elf_params *params;
>> > +
>> > /* Short-cuts to get to dynamic linker sections. */
>> > asection *sdyntdata;
>> >
>> > @@ -157,6 +160,13 @@ struct riscv_elf_link_hash_table
>> > && elf_hash_table_id (elf_hash_table (p)) == RISCV_ELF_DATA) \
>> > ? (struct riscv_elf_link_hash_table *) (p)->hash : NULL)
>> >
>> > +void
>> > +riscv_elfNN_set_options (struct bfd_link_info *link_info,
>> > + struct riscv_elf_params *params)
>> > +{
>> > + riscv_elf_hash_table (link_info)->params = params;
>> > +}
>> > +
>> > static bool
>> > riscv_info_to_howto_rela (bfd *abfd,
>> > arelent *cache_ptr,
>> > @@ -4289,7 +4299,9 @@ _bfd_riscv_relax_lui (bfd *abfd,
>> > bool undefined_weak)
>> > {
>> > bfd_byte *contents = elf_section_data (sec)->this_hdr.contents;
>> > - bfd_vma gp = riscv_global_pointer_value (link_info);
>> > + bfd_vma gp = riscv_elf_hash_table (link_info)->params->relax_gp
>> > + ? riscv_global_pointer_value (link_info)
>> > + : 0;
>> > int use_rvc = elf_elfheader (abfd)->e_flags & EF_RISCV_RVC;
>> >
>> > BFD_ASSERT (rel->r_offset + 4 <= sec->size);
>> > @@ -4754,10 +4766,10 @@ _bfd_riscv_relax_section (bfd *abfd, asection *sec,
>> > || type == R_RISCV_TPREL_LO12_I
>> > || type == R_RISCV_TPREL_LO12_S)
>> > relax_func = _bfd_riscv_relax_tls_le;
>> > - else if (!bfd_link_pic (info)
>
>Probably just add "riscv_elf_hash_table (info)->params->relax_gp"
>here, to make the coding style same as above.
I'm going to use:
else if (!bfd_link_pic (info) && htab->params->relax_gp
&& (type == R_RISCV_PCREL_HI20
...
>> > - && (type == R_RISCV_PCREL_HI20
>> > - || type == R_RISCV_PCREL_LO12_I
>> > - || type == R_RISCV_PCREL_LO12_S))
>> > + else if ((type == R_RISCV_PCREL_HI20 || type == R_RISCV_PCREL_LO12_I
>> > + || type == R_RISCV_PCREL_LO12_S)
>> > + && !bfd_link_pic (info)
>> > + && riscv_elf_hash_table (info)->params->relax_gp)
>> > relax_func = _bfd_riscv_relax_pc;
>> > else
>> > continue;
>> > diff --git a/bfd/elfxx-riscv.h b/bfd/elfxx-riscv.h
>> > index ea7126bdb4d..f9bd0ad882c 100644
>> > --- a/bfd/elfxx-riscv.h
>> > +++ b/bfd/elfxx-riscv.h
>> > @@ -27,6 +27,17 @@
>> >
>> > #define RISCV_UNKNOWN_VERSION -1
>> >
>> > +struct riscv_elf_params
>> > +{
>> > + /* Whether to relax code sequences to GP-relative addressing. */
>> > + bool relax_gp;
>> > +};
>> > +
>> > +extern void riscv_elf32_set_options (struct bfd_link_info *,
>> > + struct riscv_elf_params *);
>> > +extern void riscv_elf64_set_options (struct bfd_link_info *,
>> > + struct riscv_elf_params *);
>> > +
>> > extern reloc_howto_type *
>> > riscv_reloc_name_lookup (bfd *, const char *);
>> >
>> > diff --git a/ld/emultempl/riscvelf.em b/ld/emultempl/riscvelf.em
>> > index 645a807f239..37a0fd08e96 100644
>> > --- a/ld/emultempl/riscvelf.em
>> > +++ b/ld/emultempl/riscvelf.em
>> > @@ -25,6 +25,35 @@ fragment <<EOF
>> > #include "elf/riscv.h"
>> > #include "elfxx-riscv.h"
>> >
>> > +static struct riscv_elf_params params = { .relax_gp = 1 };
>> > +EOF
>> > +
>> > +# Define some shell vars to insert bits of code into the standard elf
>> > +# parse_args and list_options functions. */
>> > +PARSE_AND_LIST_PROLOGUE=${PARSE_AND_LIST_PROLOGUE}'
>> > +enum risccv_opt
>> > +{
>> > + OPTION_RELAX_GP = 321,
>> > + OPTION_NO_RELAX_GP,
>> > +};
>> > +'
>
>Not really sure if the value of base enum is flexible or has some
>meaning. I see ppc starts with 321, mips and nds32 start with 301,
>and aarch64 starts with 309. If the start value doesn't mean
>anything, then it's fine here.
I think the start value is arbitrary. I stick with the ppc style which is
well maintained by Alan :)
>> > +
>> > +PARSE_AND_LIST_LONGOPTS=${PARSE_AND_LIST_LONGOPTS}'
>> > + { "relax-gp", no_argument, NULL, OPTION_RELAX_GP },
>> > + { "no-relax-gp", no_argument, NULL, OPTION_NO_RELAX_GP },
>> > +'
>> > +
>
>It's good to also define PARSE_AND_LIST_OPTIONS, so that --target-help
>should work for the new options.
Ack. I did not know PARSE_AND_LIST_OPTIONS.
PARSE_AND_LIST_OPTIONS=${PARSE_AND_LIST_OPTIONS}'
fprintf (file, _(" --relax-gp Perform GP relaxation\n"));
fprintf (file, _(" --no-relax-gp Don'\''t perform GP relaxation\n"));
'
>> > +PARSE_AND_LIST_ARGS_CASES=${PARSE_AND_LIST_ARGS_CASES}'
>> > + case OPTION_RELAX_GP:
>> > + params.relax_gp = 1;
>> > + break;
>> > +
>> > + case OPTION_NO_RELAX_GP:
>> > + params.relax_gp = 0;
>> > + break;
>> > +'
>> > +
>> > +fragment <<EOF
>> > static void
>> > riscv_elf_before_allocation (void)
>> > {
>> > @@ -96,6 +125,8 @@ riscv_create_output_section_statements (void)
>> > " whilst linking %s binaries\n"), "RISC-V");
>> > return;
>> > }
>> > +
>> > + riscv_elf${ELFSIZE}_set_options (&link_info, ¶ms);
>> > }
>> >
>> > EOF
>> > diff --git a/ld/testsuite/ld-riscv-elf/code-model-relax-medlow-01-norelaxgp.d b/ld/testsuite/ld-riscv-elf/code-model-relax-medlow-01-norelaxgp.d
>> > new file mode 100644
>> > index 00000000000..8e40cc5f32d
>> > --- /dev/null
>> > +++ b/ld/testsuite/ld-riscv-elf/code-model-relax-medlow-01-norelaxgp.d
>> > @@ -0,0 +1,4 @@
>> > +#source: code-model.s
>> > +#as: -march=rv64i -mabi=lp64 --defsym __medlow__=1
>> > +#ld: -Tcode-model-01.ld -melf64lriscv --no-relax-gp --relax
>> > +#error: .*relocation truncated to fit: R_RISCV_HI20 against `symbolL'
>> > diff --git a/ld/testsuite/ld-riscv-elf/ld-riscv-elf.exp b/ld/testsuite/ld-riscv-elf/ld-riscv-elf.exp
>> > index 272424b33e3..1711d12ba23 100644
>> > --- a/ld/testsuite/ld-riscv-elf/ld-riscv-elf.exp
>> > +++ b/ld/testsuite/ld-riscv-elf/ld-riscv-elf.exp
>> > @@ -122,6 +122,7 @@ if [istarget "riscv*-*-*"] {
>> > run_dump_test "align-small-region"
>> > run_dump_test "call-relax"
>> > run_dump_test "pcgp-relax-01"
>> > + run_dump_test "pcgp-relax-01-norelaxgp"
>> > run_dump_test "pcgp-relax-02"
>> > run_dump_test "c-lui"
>> > run_dump_test "c-lui-2"
>> > @@ -141,6 +142,7 @@ if [istarget "riscv*-*-*"] {
>> > run_dump_test "code-model-medany-weakref-01"
>> > run_dump_test "code-model-medany-weakref-02"
>> > run_dump_test "code-model-relax-medlow-01"
>> > + run_dump_test "code-model-relax-medlow-01-norelaxgp"
>> > run_dump_test "code-model-relax-medlow-02"
>> > run_dump_test "code-model-relax-medlow-weakref-01"
>> > run_dump_test "code-model-relax-medlow-weakref-02"
>> > diff --git a/ld/testsuite/ld-riscv-elf/pcgp-relax-01-norelaxgp.d b/ld/testsuite/ld-riscv-elf/pcgp-relax-01-norelaxgp.d
>> > new file mode 100644
>> > index 00000000000..d1344576ff3
>> > --- /dev/null
>> > +++ b/ld/testsuite/ld-riscv-elf/pcgp-relax-01-norelaxgp.d
>> > @@ -0,0 +1,18 @@
>> > +#source: pcgp-relax-01.s
>> > +#ld: --no-relax-gp --relax
>> > +#objdump: -d -Mno-aliases
>> > +
>> > +.*:[ ]+file format .*
>> > +
>> > +
>> > +Disassembly of section \.text:
>> > +
>> > +0+[0-9a-f]+ <_start>:
>> > +.*:[ ]+[0-9a-f]+[ ]+addi[ ]+a0,a0,[0-9]+
>> > +.*:[ ]+[0-9a-f]+[ ]+jal[ ]+ra,[0-9a-f]+ <_start>
>> > +.*:[ ]+[0-9a-f]+[ ]+auipc[ ]+a1,0x[0-9a-f]+
>> > +.*:[ ]+[0-9a-f]+[ ]+addi[ ]+a1,a1,[0-9]+ # [0-9a-f]+ <data_g>
>> > +.*:[ ]+[0-9a-f]+[ ]+lui[ ]+a2,0x[0-9a-f]+
>> > +.*:[ ]+[0-9a-f]+[ ]+addi[ ]+a2,a2,[0-9]+ # [0-9a-f]+ <data_g>
>> > +.*:[ ]+[0-9a-f]+[ ]+addi[ ]+a3,tp,0 # 0 <data_t>
>> > +.*:[ ]+[0-9a-f]+[ ]+auipc[ ]+a0,0x[0-9a-f]+
>> > diff --git a/ld/testsuite/ld-riscv-elf/pcgp-relax-02.d b/ld/testsuite/ld-riscv-elf/pcgp-relax-02.d
>> > index c6c73c54265..984d457aed9 100644
>> > --- a/ld/testsuite/ld-riscv-elf/pcgp-relax-02.d
>> > +++ b/ld/testsuite/ld-riscv-elf/pcgp-relax-02.d
>> > @@ -1,6 +1,6 @@
>> > #source: pcgp-relax-02.s
>> > #as:
>> > -#ld: --relax
>> > +#ld: --relax --relax-gp
>> > #objdump: -d
>> >
>> > .*:[ ]+file format .*
>> > --
>> > 2.37.0.144.g8ac04bfd2-goog
>> >
>>
>> Ping. I maintain lld/ELF and we are considering a new opt-in option
>> --relax-gp to perform GP relaxation.
>> It will be opt-in since many users don't find the relaxation useful
>> and some feel GP relaxation will conflict with using GP for other
>> purposes (some ABI variants).
>> I wish that the two linkers agree on the same options.
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