[PATCH v5] Add retain attribute to place symbols in SHF_GNU_RETAIN section

H.J. Lu hjl.tools@gmail.com
Wed Feb 17 20:50:35 GMT 2021


On Wed, Feb 17, 2021 at 12:14 PM Jakub Jelinek <jakub@redhat.com> wrote:
>
> On Wed, Feb 17, 2021 at 12:04:34PM -0800, H.J. Lu wrote:> >
> > +  /* For -fretain-used-symbol, a "used" attribute also implies "retain".  */
>
> s/-symbol/-symbols/

Fixed.

> > +  if (flag_retain_used_symbols
> > +      && attributes
> > +      && (TREE_CODE (*node) == FUNCTION_DECL
> > +       || (VAR_P (*node) && TREE_STATIC (*node))
> > +       || (TREE_CODE (*node) == TYPE_DECL))
>
> What will "retain" do on TYPE_DECLs?  It only makes sense to me
> for FUNCTION_DECL or non-automatic VAR_DECLs, unless for types
> it means the types with that result in vars with those types automatically
> getting "retain", but there is no code for that and I don't see "used"
> handled that way.

Fixed.

> > +  if (SUPPORTS_SHF_GNU_RETAIN
> > +      && (TREE_CODE (node) == FUNCTION_DECL
> > +       || (VAR_P (node) && TREE_STATIC (node))
> > +       || (TREE_CODE (node) == TYPE_DECL)))
>
> Likewise.

Fixed.

> > +    ;
> > +  else
> > +    {
> > +      warning (OPT_Wattributes, "%qE attribute ignored", name);
> > +      *no_add_attrs = true;
> > +    }
> > +
> > +  return NULL_TREE;
> > +}
> > +
> >  /* Handle a "externally_visible" attribute; arguments as in
> >     struct attribute_spec.handler.  */
> >
> > diff --git a/gcc/common.opt b/gcc/common.opt
> > index c75dd36843e..70842481d4d 100644
> > --- a/gcc/common.opt
> > +++ b/gcc/common.opt
> > @@ -2404,6 +2404,10 @@ frerun-loop-opt
> >  Common Ignore
> >  Does nothing.  Preserved for backward compatibility.
> >
> > +fretain-used-symbols
> > +Common Var(flag_retain_used_symbols)
> > +Make the used attribute to imply the retain attribute if supported.
>
> English is not my native language, but I think the "to " doesn't belong
> here.

Fixed.

> > +@item -fretain-used-symbols
> > +@opindex fretain-used-symbols
> > +On systems with recent GNU assembler and linker, the compiler makes
>
> I think we should avoid recent here, new/old/recent etc. are relative terms.
> Either use exact version (is it 2.36 or later) or say GNU assembler and
> linker that supports the @code{.retain} directive or something similar.

Fixed.

> >    flags |= SECTION_NAMED;
> > -  if (SUPPORTS_SHF_GNU_RETAIN
> > -      && decl != nullptr
> > +  if (decl != nullptr
> >        && DECL_P (decl)
> > -      && DECL_PRESERVE_P (decl))
> > +      && DECL_PRESERVE_P (decl)
> > +      && lookup_attribute ("retain", DECL_ATTRIBUTES (decl)))
> >      flags |= SECTION_RETAIN;
> >    if (*slot == NULL)
> >      {
>
> I think none of the varasm.c code should use DECL_PRESERVE_P when it means
> retain, just lookup_attribute.

Fixed.

> > @@ -487,7 +487,8 @@ resolve_unique_section (tree decl, int reloc ATTRIBUTE_UNUSED,
> >    if (DECL_SECTION_NAME (decl) == NULL
> >        && targetm_common.have_named_sections
> >        && (flag_function_or_data_sections
> > -       || (SUPPORTS_SHF_GNU_RETAIN && DECL_PRESERVE_P (decl))
> > +       || (DECL_PRESERVE_P (decl)
> > +           && lookup_attribute ("retain", DECL_ATTRIBUTES (decl)))
> >         || DECL_COMDAT_GROUP (decl)))
> >      {
> >        targetm.asm_out.unique_section (decl, reloc);
> > @@ -1227,7 +1228,8 @@ get_variable_section (tree decl, bool prefer_noswitch_p)
> >      vnode->get_constructor ();
> >
> >    if (DECL_COMMON (decl)
> > -      && !(SUPPORTS_SHF_GNU_RETAIN && DECL_PRESERVE_P (decl)))
> > +      && !(DECL_PRESERVE_P (decl)
> > +        && lookup_attribute ("retain", DECL_ATTRIBUTES (decl))))
> >      {
> >        /* If the decl has been given an explicit section name, or it resides
> >        in a non-generic address space, then it isn't common, and shouldn't
> > @@ -7761,12 +7763,14 @@ switch_to_section (section *new_section, tree decl)
> >  {
> >    if (in_section == new_section)
> >      {
> > -      if (SUPPORTS_SHF_GNU_RETAIN
> > -       && (new_section->common.flags & SECTION_NAMED)
> > +      if ((new_section->common.flags & SECTION_NAMED)
> >         && decl != nullptr
> >         && DECL_P (decl)
> >         && (!!DECL_PRESERVE_P (decl)
> > -           != !!(new_section->common.flags & SECTION_RETAIN)))
> > +           != !!(new_section->common.flags & SECTION_RETAIN))
> > +       && (lookup_attribute ("retain",
> > +                             DECL_ATTRIBUTES (new_section->named.decl))
> > +           || lookup_attribute ("retain", DECL_ATTRIBUTES (decl))))
> >       {
> >         /* If the SECTION_RETAIN bit doesn't match, switch to a new
> >            section.  */
> > --
> > 2.29.2
> >

Here is the updated patch.

-- 
H.J.
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