Re: [PATCH]: Allow relative calculations for non-R_*_RELATIVE relocs.

[Ian Lance Taylor <iant at google dot com>]

David Miller <davem@davemloft.net> writes:

> 2010-02-12  David S. Miller  <davem@davemloft.net>
>
> 	* output.h (Output_reloc<SHT_REL>::Output_reloc): Add
> 	is_symbolless parameter.
> 	(Output_reloc<SHT_REL>::is_symbolless): New.
> 	(Output_reloc<SHT_REL>::is_symbolless_): New.
> 	(Output_reloc<SHT_RELA>::Output_reloc): Add is_symbolless parameter.
> 	(Output_reloc<SHT_RELA>::is_symbolless): New.
> 	(Output_data_reloc::add_global): Handle is_symbolless.
> 	(Output_data_reloc::add_global_relative): Likewise.
> 	(Output_data_reloc::add_local): Likewise.
> 	(Output_data_reloc::add_local_relative): Likewise.
> 	(Output_data_reloc::add_symbolless_global_addend): New.
> 	(Output_data_reloc::add_symbolless_local_addend): New.
> 	* output.cc (Output_reloc<SHT_REL>::Output_reloc): Handle
> 	is_symbolless.
> 	(Output_reloc::set_needs_dynsym_index): Test ->is_symbolless_
> 	instead of ->is_relative_
> 	(Output_reloc::write_rel): Likewise.
> 	(Output_reloc::write): Likewise.
> 	(Output_reloc::compare): Do not attempt to sort by symbol index when
> 	->is_symbolless is true.
>
> 	* sparc.cc (Target_sparc::Scan::local): Use
> 	->add_symbolless_local_addend as needed.
> 	(Target_sparc::Scan::global): Use ->add_symbolless_global_addend as
> 	needed.  Also, emit appropriate unaligned vs. aligned dynamic reloc
> 	based upon relocation offset.


> @@ -1053,7 +1066,8 @@ Output_reloc<elfcpp::SHT_REL, dynamic, size, big_endian>::
>      }
>    else if (r2.is_relative_)
>      return 1;
> -  else
> +  else if (!this->is_symbolless_
> +	   && !r2.is_symbolless_)
>      {
>        unsigned int sym1 = this->get_symbol_index();
>        unsigned int sym2 = r2.get_symbol_index();

I think we should sort symbolless relocs after relative relocs but
before other relocs.  That is, instead of doing this, do

  else
    {
      unsigned int sym1 = this->is_symbolless_ ? 0 : this->get_symbol_index();
      unsigned int sym2 = r2.is_symbolless_ ? 0 : r2.get_symbol_index();

Or it might be simpler to just change get_symbol_index() to check
is_symbolless_, and then simplify write_rel().  Either way is fine
with me.


> +  // Return whether this is a relocation which should not use
> +  // a symbol, but which obtains it's addend from a symbol.
> +  bool
> +  is_symbolless() const
> +  { return this->is_symbolless_; }

s/it's/its/


> @@ -1155,6 +1162,9 @@ class Output_reloc<elfcpp::SHT_REL, dynamic, size, big_endian>
>    unsigned int type_ : 30;
>    // True if the relocation is a RELATIVE relocation.
>    bool is_relative_ : 1;
> +  // True if the relocation is one which should not use
> +  // a symbol, but which obtains it's addend from a symbol.
> +  bool is_symbolless_ : 1;
>    // True if the relocation is against a section symbol.
>    bool is_section_symbol_ : 1;
>    // If the reloc address is an input section in an object, the

s/it's/its/

Also this is going to make the struct one word larger.  Please change
type_ to be a 29-bit bitfield.  That should be fine in practice, and
the code already double-checks that the r_type value fits in the
field.


> +  // Return whether this is a relocation which should not use
> +  // a symbol, but which obtains it's addend from a symbol.
> +  bool
> +  is_symbolless() const
> +  { return this->rel_.is_symbolless(); }

s/it's/its/


> +  // Add a global relocation which does not use a symbol for the relocation,
> +  // but which gets it's addend from a symbol.

s/it's/its/


This is OK with those changes.

Thanks.

Ian