Re: Specify how undefined weak symbol should be resolved in executable

["H.J. Lu" <hjl.tools@gmail.com>]

On Mon, Feb 22, 2016 at 2:43 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Mon, Feb 22, 2016 at 10:28 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
>> On Mon, Feb 22, 2016 at 10:17 AM, Michael Matz <matz@suse.de> wrote:
>>> Hi,
>>>
>>> On Mon, 22 Feb 2016, H.J. Lu wrote:
>>>
>>>> > Typo?  What is the meaning of "dynamic relocation available at
>>>> > runtime". Are you talking about a relocation entry or the relocation
>>>> > process?
>>>>
>>>> Dynamic relocation isn't available with static linking.
>>>
>>> So you _are_ talking about the process.  I think it's customary to call
>>> such executables "dynamic", or perhaps non-static, isn't it?  (Why I'm
>>> confused with your wording: a dynamic executable which happens to have no
>>> dynamic reloc entries, has "no dynamic relocation available at runtime",
>>> and so we couldn't add one :))
>>>
>>>> > How about "When creating a dynamic executable the link editor should
>>>> > ..."?
>>>
>>> So, I still can understand my version better (possibly with
>>> s/dynamic/non-static/) :)
>>>
>>
>> Let's go with:
>>
>> When creating dynamic executable, the link editor should generate dynamic
>> relocations against unresolved weak symbols so that their values will be
>> resolved at run-time.
>>
>
> Second thought.  To generate dynamic relocation for R_X86_64_32
> against fun in:
>
> [hjl@gnu-6 pr19704]$ objdump -dwr foo.o
>
> foo.o:     file format elf64-x86-64
>
>
> Disassembly of section .text.startup:
>
> 0000000000000000 <main>:
>    0: b8 00 00 00 00       mov    $0x0,%eax 1: R_X86_64_32 fun
>    5: 48 85 c0             test   %rax,%rax
>    8: 74 10                 je     1a <main+0x1a>
>    a: 48 83 ec 08           sub    $0x8,%rsp
>    e: e8 00 00 00 00       callq  13 <main+0x13> f: R_X86_64_PC32 fun-0x4
>   13: 31 c0                 xor    %eax,%eax
>   15: 48 83 c4 08           add    $0x8,%rsp
>   19: c3                   retq
>   1a: 31 c0                 xor    %eax,%eax
>   1c: c3                   retq
> [hjl@gnu-6 pr19704]$
>
> we create executable with dynamic R_X86_64_32 relocation against
> fun .text section, which leads to DT_TEXTREL.  Is this what we want?
>

I believe the intention of undefined weak symbol is it should be resolved
at link-time when creating executable, dynamic or static.

-- 
H.J.