RFC: [PATCH] ELF: Don't require section header on ELF objects

[H.J. Lu]

On Mon, Mar 9, 2020 at 3:43 PM Alan Modra <amodra@gmail.com> wrote:
>
> On Tue, Mar 10, 2020 at 12:24:51AM +1030, Kaylee Blake wrote:
> > On 10/3/20 12:14 am, Alan Modra wrote:
> > > On Mon, Mar 09, 2020 at 11:24:44PM +1030, Kaylee Blake wrote:
> > >> On 9/3/20 6:43 pm, Florian Weimer wrote:
> > >>> In my opinion, it should NOT be possible to link against objects
> > >>> without section headers.  Lack of section headers clearly marks the
> > >>> object as a run-time only object.  This is useful if you want to
> > >>> prevent developers to create DT_NEEDED dependencies on internal
> > >>> libraries, for example.
> > >
> > > I agree.
> > >
> > >> For shared objects without debug symbols, the section header table is
> > >> ~2kB on average of redundant data. I'm also not a fan of the
> > >> inconsistency of having shared libraries that the dynamic linker is
> > >> perfectly happy to load, but ld can't link against, especially since
> > >> this seems like an oversight rather than an intended design decision.
> > >
> > > The ELF spec designed things that way.  See figure 4.1 which I'll try
> > > to represent in text.
> > >
> > > Figure 4-1: Object File Format
> > >
> > > |----------------------|    |----------------------|
> > > |      ELF Header      |    |      ELF Header      |
> > > |----------------------|    |----------------------|
> > > | Program header table |    | Program header table |
> > > |       optional       |    |       required       |
> > > |----------------------|    |----------------------|
> > > |       Section 1      |    |       Segment 1      |
> > > |----------------------|    |----------------------|
> > > |          ...         |    |       Segment 2      |
> > > |----------------------|    |----------------------|
> > > |       Section n      |    |       Segment 3      |
> > > |----------------------|    |----------------------|
> > > |          ...         |    |          ...         |
> > > |----------------------|    |----------------------|
> > > | Section header table |    | Section header table |
> > > |       required       |    |       optional       |
> > > |----------------------|    |----------------------|
> > >       Linking View               Execution View
> > >
> >
> > I had interpreted that table in combination to various other references
> > to which things are required vs optional in shared objects as meaning
> > that the "execution view" applied to executables and shared objects, and
> > the "linking view" applied to relocatable objects. You're saying that
> > that table should be interpreted as saying that if a shared object is to
> > be linkable, the spec is requiring it to have both sets of headers?
>
> Yes.  Just below the table: "Files used during linking must have a
> section header table".
>

I posted a new set of patches without linker support for PT_DYNAMIC:

https://sourceware.org/pipermail/binutils/2020-March/110157.html

-- 
H.J.