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List:       binutils
Subject:    Re: [PATCH 2/2] RISC-V: Enable x0 base relaxation for relax_pc even if --no-relax-gp.
From:       Kito Cheng via Binutils <binutils () sourceware ! org>
Date:       2023-04-28 7:14:24
Message-ID: CA+yXCZABRzH=CAsWgukYiwv4W5rrGEStYjYP6ciGYiggqomb3w () mail ! gmail ! com
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it called Zero-page Relaxation on psABI spec
 https://github.com/riscv-non-isa/riscv-elf-psabi-doc/blob/master/riscv-elf.adoc#zero-page-relaxation

On Fri, Apr 28, 2023 at 3:11 PM Fangrui Song <i@maskray.me> wrote:
>
> On Thu, Apr 27, 2023 at 11:29 PM Nelson Chu <nelson@rivosinc.com> wrote:
> >
> > Committed, thanks.
> >
> > Nelson
>
> Thanks. I cannot find any information about "x0 base relaxation" on
> the Internet.
> It is worth a test: if I force `bfd_vma gp = 0;`, check-ld
> RUNTESTFLAGS='ld-riscv-elf.exp' will still pass :)
>
> > On Fri, Apr 21, 2023 at 4:28 PM Nelson Chu <nelson@rivosinc.com> wrote:
> >
> > > Let --no-relax-gp only disable the gp relaxation for lui and pcrel
> > > relaxations, since x0 base and gp relaxations are different optimizations
> > > in fact, but just use the same function to handle.
> > >
> > > bfd/
> > >         * elfnn-riscv.c (_bfd_riscv_relax_pc): Like _bfd_riscv_relax_lui,
> > >         set gp to zero when --no-relax-gp, then we should still keep the
> > >         x0 base relaxation.
> > >         (_bfd_riscv_relax_section): Enable _bfd_riscv_relax_pc when
> > >         --no-relax-gp, we will disable the gp relaxation in the
> > >         _bfd_riscv_relax_pc.
> > > ---
> > >  bfd/elfnn-riscv.c | 6 ++++--
> > >  1 file changed, 4 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/bfd/elfnn-riscv.c b/bfd/elfnn-riscv.c
> > > index 499f51ee857..77a732b6a08 100644
> > > --- a/bfd/elfnn-riscv.c
> > > +++ b/bfd/elfnn-riscv.c
> > > @@ -4721,7 +4721,9 @@ _bfd_riscv_relax_pc (bfd *abfd ATTRIBUTE_UNUSED,
> > >                      bool undefined_weak)
> > >  {
> > >    struct riscv_elf_link_hash_table *htab = riscv_elf_hash_table
> > > (link_info);
> > > -  bfd_vma gp = riscv_global_pointer_value (link_info);
> > > +  bfd_vma gp = htab->params->relax_gp
> > > +              ? riscv_global_pointer_value (link_info)
> > > +              : 0;
> > >
> > >    BFD_ASSERT (rel->r_offset + 4 <= sec->size);
> > >
> > > @@ -4942,7 +4944,7 @@ _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) && htab->params->relax_gp
> > > +         else if (!bfd_link_pic (info)
> > >                    && (type == R_RISCV_PCREL_HI20
> > >                        || type == R_RISCV_PCREL_LO12_I
> > >                        || type == R_RISCV_PCREL_LO12_S))
> > > --
> > > 2.39.2 (Apple Git-143)
> > >
> > >
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