From: Kaylee Blake <klkblake@gmail.com>
To: binutils@sourceware.org
Subject: Re: RFC: [PATCH] ELF: Don't require section header on ELF objects
Date: Mon, 9 Mar 2020 23:58:59 +1030 [thread overview]
Message-ID: <b41c2761-8a32-1a57-c70a-123076903257@gmail.com> (raw)
In-Reply-To: <87y2s98y94.fsf@mid.deneb.enyo.de>
On 9/3/20 11:46 pm, Florian Weimer wrote:
> * Kaylee Blake:
>
>> On 9/3/20 11:36 pm, Florian Weimer wrote:
>>> * Kaylee Blake:
>>>
>>>> On 9/3/20 6:43 pm, Florian Weimer wrote:
>>>>> * H. J. Lu:
>>>>>
>>>>>> Section header isn't mandatory on ELF executable nor shared library.
>>>>>> This patch adds a new linker option, -z nosectionheader, to omit ELF
>>>>>> section header when building an executable or shared library, adds
>>>>>> an objcopy and strip option, --remove-section-header, to remove ELF
>>>>>> section header from an executable or shared library.
>>>>>>
>>>>>> The PT_DYNAMIC segment contains DT_HASH/DT_GNU_HASH/DT_MIPS_XHASH,
>>>>>> DT_STRTAB, DT_SYMTAB, DT_STRSZ and DT_SYMENT, which can be used to
>>>>>> reconstruct dynamic symbol table when section header isn't available.
>>>>>> For DT_HASH, the number of dynamic symbol table entries equals the
>>>>>> number of chains. For DT_GNU_HASH/DT_MIPS_XHASH, only defined symbols
>>>>>> with non-STB_LOCAL indings are in hash table. Since in dynamic symbol
>>>>>> table, all symbols with STB_LOCAL binding are placed before symbols with
>>>>>> other bindings and all defined symbols are placed before undefined ones,
>>>>>> the highest symbol index in DT_GNU_HASH/DT_MIPS_XHASH is the highest
>>>>>> dynamic symbol table index.
>>>>>
>>>>> Does this patch enable ld to use shared objects without a section
>>>>> header for linking?
>>>>>
>>>>> I think the NEWS and manual update should clarify this.
>>>>>
>>>>> 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.
>>>>
>>>> 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.
>>>
>>> You didn't answer my question. 8-)
>>
>> Ah, yes, sorry. It does enable that; that was my primary motivation for
>> my part in it.
>
> I think that's conceptually the wrong thing to do for ELF, sorry. If
> there is no section header, the object should be unlinkable. The
> linker should not use the dynamic segment to locate the symbol
> information, only the dynamic section (in case the link ABI and
> run-time ABI are different).
I'm confused by your comment about link and run-time ABIs differing;
surely if the ABI at runtime differs from the ABI at link time, you are
just going to crash at runtime?
--
Kaylee Blake <klkblake@gmail.com>
C is the worst language, except for all the others.
next prev parent reply other threads:[~2020-03-09 13:29 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 [this message]
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
2020-03-10 0:14 ` H.J. Lu
2020-03-09 14:34 ` Michael Matz
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