From: Alan Modra <amodra@gmail.com>
To: Kaylee Blake <klkblake@gmail.com>
Cc: binutils@sourceware.org
Subject: Re: RFC: [PATCH] ELF: Don't require section header on ELF objects
Date: Tue, 10 Mar 2020 09:04:49 +1030 [thread overview]
Message-ID: <20200309223449.GQ5384@bubble.grove.modra.org> (raw)
In-Reply-To: <871cf36a-5690-a8a7-68af-2cf0f54c5b5d@gmail.com>
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".
--
Alan Modra
Australia Development Lab, IBM
next prev parent reply other threads:[~2020-03-09 22:34 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-08 17:59 H.J. Lu
2020-03-08 18:06 ` H.J. Lu
2020-03-08 23:35 ` Alan Modra
2020-03-08 23:46 ` H.J. Lu
2020-03-09 0:02 ` H.J. Lu
2020-03-09 0:02 ` Kaylee Blake
2020-03-09 0:05 ` Alan Modra
2020-03-09 1:36 ` H.J. Lu
2020-03-09 1:59 ` Kaylee Blake
2020-03-09 2:23 ` Alan Modra
2020-03-09 2:35 ` H.J. Lu
2020-03-09 4:14 ` H.J. Lu
2020-03-09 4:59 ` Kaylee Blake
2020-03-09 11:56 ` Alan Modra
2020-03-08 23:24 ` Kaylee Blake
2020-03-08 23:29 ` H.J. Lu
2020-03-08 23:38 ` Alan Modra
2020-03-08 23:45 ` H.J. Lu
2020-03-12 2:14 ` Fangrui Song
2020-03-09 8:13 ` Florian Weimer
2020-03-09 12:54 ` Kaylee Blake
2020-03-09 13:06 ` Florian Weimer
2020-03-09 13:14 ` Kaylee Blake
2020-03-09 13:16 ` Florian Weimer
2020-03-09 13:28 ` Kaylee Blake
2020-03-09 13:29 ` Florian Weimer
2020-03-09 13:45 ` Kaylee Blake
2020-03-09 13:54 ` H.J. Lu
2020-03-09 14:02 ` Kaylee Blake
2020-03-09 14:52 ` Florian Weimer
2020-03-09 15:07 ` Kaylee Blake
2020-03-09 15:29 ` Florian Weimer
2020-03-09 13:44 ` Alan Modra
2020-03-09 13:54 ` Kaylee Blake
2020-03-09 22:34 ` Alan Modra [this message]
2020-03-10 0:14 ` H.J. Lu
2020-03-09 14:34 ` Michael Matz
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