Re: [PATCH] Ver.2: Add compile option "-msmall-data-limit=0" to avoid using .srodata section for riscv.

[Oria Chiuan <oriachiuan@gmail.com>]

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Thank you very much for your patient explanation！

Palmer Dabbelt <palmer@dabbelt.com>于2022年11月18日 周五13:02写道：

> On Thu, 17 Nov 2022 19:30:23 PST (-0800), oriachiuan@gmail.com wrote:
> > Got it, I used to regard this test case as targeting at test if the const
> > data would use the ".rodata" section.
>
> Sorry, I'm not quite sure what you're trying to say here.  Here's a dump
> of how I see things:
>
> In some targets (RISC-V and MIPS) there's multiple copies of the
> data/rodata sections, with the small data/rodata ending up in the small
> sections (`.sdata` and `.srodata`).  I've never actually been 100% on
> that being allowed by any spec, but MIPS did it long before RISC-V so I
> figure software is expected to tolerate the oddness.
>
> In RISC-V we use it to try and place as many symbols as possible close
> to GP, so we're more likely to relax to GP-relative addressing
> sequences.  IIRC that's pretty much the same as MIPS, though they have
> slightly different addressing requirements.
>
> For targets that function this way `.srodata` and `.rodata` are
> functionally equivalent (assuming you're not playing any GP tricks to
> relocate, but those are way out of what's supported).  So unless the
> test is trying to dig into performance issues differences between these
> sections, it should just allow code to target either.
>
> >
> > Palmer Dabbelt <palmer@dabbelt.com> 于2022年11月18日周五 07:59写道：
> >
> >> On Thu, 17 Nov 2022 13:50:00 PST (-0800), gcc-patches@gcc.gnu.org
> wrote:
> >> >
> >> > On 11/17/22 02:53, Yixuan Chen wrote:
> >> >> 2022-11-17  Yixuan Chen  <chenyixuan@iscas.ac.cn>
> >> >>
> >> >>          * gcc/testsuite/gcc.dg/pr25521.c: Add compile option
> >> "-msmall-data-limit=0" to avoid using .srodata section for riscv.
> >> >> ---
> >> >>   gcc/testsuite/gcc.dg/pr25521.c | 3 ++-
> >> >>   1 file changed, 2 insertions(+), 1 deletion(-)
> >> >>
> >> >> diff --git a/gcc/testsuite/gcc.dg/pr25521.c
> >> b/gcc/testsuite/gcc.dg/pr25521.c
> >> >> index 74fe2ae6626..628ddf1a761 100644
> >> >> --- a/gcc/testsuite/gcc.dg/pr25521.c
> >> >> +++ b/gcc/testsuite/gcc.dg/pr25521.c
> >> >> @@ -2,7 +2,8 @@
> >> >>      sections.
> >> >>
> >> >>      { dg-require-effective-target elf }
> >> >> -   { dg-do compile } */
> >> >> +   { dg-do compile }
> >> >> +   { dg-options "-msmall-data-limit=0" { target { riscv*-*-* } } }
> */
> >> >>
> >> >>   const volatile int foo = 30;
> >> >>
> >> >
> >> > Wouldn't this be better?  It avoids a target specific conditional by
> >> > instead extending what we look for to cover [s]rodata sections.
> >> >
> >> >
> >> > Thoughts?
> >> >
> >> > Jeff
> >> > diff --git a/gcc/testsuite/gcc.dg/pr25521.c
> >> b/gcc/testsuite/gcc.dg/pr25521.c
> >> > index 74fe2ae6626..63363a03b9f 100644
> >> > --- a/gcc/testsuite/gcc.dg/pr25521.c
> >> > +++ b/gcc/testsuite/gcc.dg/pr25521.c
> >> > @@ -7,4 +7,4 @@
> >> >  const volatile int foo = 30;
> >> >
> >> >
> >> > -/* { dg-final { scan-assembler "\\.rodata" } } */
> >> > +/* { dg-final { scan-assembler "\\.s\?rodata" } } */
> >>
> >> That's how I usually do it for these tests, there's some other targets
> >> with sdata too so it fixes the test for everyone.  IIRC I said something
> >> like that in the v1, but sorry if I'm just getting it confused with some
> >> other patch.
> >>
> >> There's a few of these that need to get chased down for every release,
> >> maybe we should add some sort of DG hepler?  Not sure that'd keep folks
> >> from matching on .data, though...
> >>
>