[PATCH v3] elf: Cache full internal symbol table for relocatable input

[H.J. Lu]

On Sat, Oct 18, 2025 at 6:23 AM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> On Fri, Oct 17, 2025 at 8:48 PM Jan Beulich <jbeulich@suse.com> wrote:
> >
> > On 11.10.2025 08:37, H.J. Lu wrote:
> > > On Sat, Oct 11, 2025 at 9:08 AM Sam James <sam@gentoo.org> wrote:
> > >>
> > >> "H.J. Lu" <hjl.tools@gmail.com> writes:
> > >>
> > >>> Add bfd_elf_get_elf_syms_cached to cache internal symbol table for
> > >>> relocatable input and use the internal symbol table cache for both local
> > >>> and global symbols to avoid swapping in the same symbol table repeatedly
> > >>> for --gc-sections.  This improves linker --gc-sections speed by ~2x for
> > >>> PR ld/33530.
> > >>>
> > >>> elf_link_input_bfd is updated to not to pass preallocated buffers to
> > >>> bfd_elf_get_elf_syms_cache.
> > >>
> > >> All tests pass now for me, including:
> > >>
> > >>                 === libctf Summary ===
> > >>
> > >> # of expected passes            39
> > >> # of unsupported tests          1
> > >>
> > >> I'll test it more in the wild tonight and tomorrow.
> > >
> > > Here is the v2 patch to keep bfd_elf_get_elf_syms interface unchanged.
> >
> > What I can't spot are provisions towards systems with little memory available,
> > like possibly 32-bit ones. (I'm sure you're aware of ld's --no-keep-memory
> > option.)

I didn't do that because bfd_elf_get_elf_syms doesn't take a linker info
pointer.   The memory usage increase is about 2%.

> >
> > In the 2nd hunk altering the body of what was bfd_elf_get_elf_syms(), may I
> > ask that in the body of the outermost if() you use an if/else-if/else chain,
> > to reduce indentation some?
>
> The only indentation change is
>
> -  if (intsym_buf == NULL)
> +  if (_bfd_mul_overflow (symcount, sizeof (Elf_Internal_Sym), &amt))
>      {
> -      if (_bfd_mul_overflow (symcount, sizeof (Elf_Internal_Sym), &amt))
> -  {
> -    bfd_set_error (bfd_error_file_too_big);
> -    goto out1;
> -  }
> -      alloc_intsym = (Elf_Internal_Sym *) bfd_malloc (amt);
> -      intsym_buf = alloc_intsym;
> -      if (intsym_buf == NULL)
> -  goto out1;
> +      bfd_set_error (bfd_error_file_too_big);
> +      goto out1;
> +    }
> +  alloc_intsym = (Elf_Internal_Sym *) bfd_malloc (amt);
> +  if (alloc_intsym == NULL)
> +    {
> +      intsym_buf = NULL;
> +      goto out1;
>      }
>
> Since we always allocate a full symbol table buffer even if intsym_buf != NULL,
> I don't see how I can avoid it.
>
> > The patch also could do with splitting up some. At the first glance it looks
> > as if e.g. the reloc-cookie related changes could as well be a separate,
> > follow-on change.
>
> The reloc-cookie related changes aren't needed anymore.
>
> Here is the v3 patch.
>
> Thanks.
>
>
> --
> H.J.



-- 
H.J.