[PATCH 1/2] RISC-V: Base for complex extension implications

[Kito Cheng]

Oh, good point, and I found actually my second patch isn't really use
that as well, let me drop that and send v2

On Fri, May 9, 2025 at 5:26 PM Nelson Chu <nelson@rivosinc.com> wrote:
>
> Yeah according to the next patch, passing rps to check_func to get the xlen is reasonable, as my pended patch did the same thing,
> https://sourceware.org/pipermail/binutils/2024-November/137651.html
>
> But passing "struct riscv_implicit_subset *t" itself to t->check_func is weird in fact.  I guess you want to use the implicit string and then do the similar stuff as my above patch, maybe something that just replaces `+' into `-' when removing the extension which is the superset.  But... the t->ext is the extension name, and is the same as the passed subset->name of check_func, that's duplicate.  Besides that, users also cannot use the information t->check_func->check_func..., since it will be an unlimited loop?  I don't know, but the only useful information for now from "struct riscv_implicit_subset *t" seems to be t->implicit_exts, which doesn't seem that useful in fact...  So until we really need it and have a real example, we can decide which arguments to pass to check_func, that's probably a better way to go.
>
> Thanks
> Nelson
>
> On Fri, May 9, 2025 at 3:40 PM Kito Cheng <kito.cheng@sifive.com> wrote:
>>
>> From: Tsukasa OI <research_trasio@irq.a4lg.com>
>>
>> Thanks to the commit 48558a5e5471 ("RISC-V: Allow nested implications for
>> extensions"), we can write complex extension implications in theory.
>> However, to actually do that, we need to pass more information to
>> check_func.
>>
>> For example, we want to imply 'Zcf' from 'F' if and only if the 'Zce'
>> extension is also enabled and XLEN is 32.  Passing rps is a way to
>> enable this.
>>
>> This commit prepares for such complex extension implications.
>>
>> bfd/ChangeLog:
>>
>>         * elfxx-riscv.c (struct riscv_implicit_subset) Move around and
>>         change check_func function prototype.
>>         (check_implicit_always): New arguments.
>>         (check_implicit_for_i): Likewise.
>>         (riscv_implicit_subsets): Add comment for this variable.
>>         (riscv_parse_add_implicit_subsets): Call check_func with
>>         new arguments.
>> ---
>>  bfd/elfxx-riscv.c | 32 +++++++++++++++++++++-----------
>>  1 file changed, 21 insertions(+), 11 deletions(-)
>>
>> diff --git a/bfd/elfxx-riscv.c b/bfd/elfxx-riscv.c
>> index 83e237c2a03..4132ecf33fb 100644
>> --- a/bfd/elfxx-riscv.c
>> +++ b/bfd/elfxx-riscv.c
>> @@ -1145,10 +1145,25 @@ riscv_elf_ignore_reloc (bfd *abfd ATTRIBUTE_UNUSED,
>>    return bfd_reloc_ok;
>>  }
>>
>> +/* Record all implicit information for the subsets.  */
>> +
>> +struct riscv_implicit_subset
>> +{
>> +  const char *ext;
>> +  const char *implicit_exts;
>> +  /* A function to determine if we need to add the implicit subset.  */
>> +  bool (*check_func) (riscv_parse_subset_t *,
>> +                     const struct riscv_implicit_subset *,
>> +                     const riscv_subset_t *);
>> +};
>> +
>>  /* Always add implicit extensions for the SUBSET.  */
>>
>>  static bool
>> -check_implicit_always (riscv_subset_t *subset ATTRIBUTE_UNUSED)
>> +check_implicit_always (riscv_parse_subset_t *rps ATTRIBUTE_UNUSED,
>> +                      const struct riscv_implicit_subset *implicit
>> +                        ATTRIBUTE_UNUSED,
>> +                      const riscv_subset_t *subset ATTRIBUTE_UNUSED)
>>  {
>>    return true;
>>  }
>> @@ -1156,21 +1171,16 @@ check_implicit_always (riscv_subset_t *subset ATTRIBUTE_UNUSED)
>>  /* Add implicit extensions only when the version of SUBSET less than 2.1.  */
>>
>>  static bool
>> -check_implicit_for_i (riscv_subset_t *subset)
>> +check_implicit_for_i (riscv_parse_subset_t *rps ATTRIBUTE_UNUSED,
>> +                     const struct riscv_implicit_subset *implicit
>> +                       ATTRIBUTE_UNUSED,
>> +                     const riscv_subset_t *subset ATTRIBUTE_UNUSED)
>>  {
>>    return (subset->major_version < 2
>>           || (subset->major_version == 2
>>               && subset->minor_version < 1));
>>  }
>>
>> -/* Record all implicit information for the subsets.  */
>> -struct riscv_implicit_subset
>> -{
>> -  const char *ext;
>> -  const char *implicit_exts;
>> -  /* A function to determine if we need to add the implicit subsets.  */
>> -  bool (*check_func) (riscv_subset_t *);
>> -};
>>  /* Please added in order since this table is only run once time.  */
>>  static struct riscv_implicit_subset riscv_implicit_subsets[] =
>>  {
>> @@ -2083,7 +2093,7 @@ riscv_parse_add_implicit_subsets (riscv_parse_subset_t *rps)
>>      {
>>        riscv_subset_t *subset = NULL;
>>        if (riscv_lookup_subset (rps->subset_list, t->ext, &subset)
>> -       && t->check_func (subset))
>> +       && t->check_func (rps, t, subset))
>>        riscv_update_subset1 (rps, subset, t->implicit_exts);
>>      }
>>  }
>> --
>> 2.34.1
>>