[BFD][PR21703]Override the new defined symbol with the old normal symbol when --allow-multiple-definition is provided

[Renlin Li]

Hi,

On 12/07/17 15:17, Renlin Li wrote:
> Hi H.J,
>
> On 11/07/17 19:04, H.J. Lu wrote:
>> On Tue, Jul 11, 2017 at 10:31 AM, Renlin Li <renlin.li@foss.arm.com> wrote:
>>> ld/ChangeLog:
>>>
>>> 2017-07-11  Renlin Li  <renlin.li@arm.com>
>>>
>>>          PR ld/21703
>>>          * testsuite/ld-elf/elf.exp : Run new test case.
>>>          * testsuite/ld-elf/pr21703-1.s: New.
>>>          * testsuite/ld-elf/pr21703-2.s: New.
>>>          * testsuite/ld-elf/pr21703.sd: New.
>>>
>>> bfd/ChangeLog:
>>>
>>> 2017-07-11  Renlin Li  <renlin.li@arm.com>
>>>
>>>
>>>          PR ld/21703
>>>          * elflink.c (_bfd_elf_merge_symbol): Handle multiple symbol
>>> definition
>>>          case.
>
>
>>
>> Please add some a test to cover versioned_sym in:
>
> This is because _bfd_elf_merge_symbol will be called for versioned symbol with the short
> name.
>
> For example, ld/testsuite/ld-elf/pr18735.s
> It defines foo and an alias foo@FOO.
> in addition to that, _bfd_elf_add_default_symbol will be called for foo@FOO to create a
> new symbol which short name (foo in this case). For the original condition, this will
> generate a multiple definition error.
>
> "matched" flag seems introduced by you. Here I use it to differentiate the versioned
> symbol case from normal symbol definition.
>
>
>>
>>    /* There are multiple definitions of a normal symbol.  */
>> +  if (olddef && !olddyn && !oldweak && newdef && !newdyn && !newweak
>> +      && !versioned_sym && h->def_regular)
>> +    {
>>
>> What should happen if symbol is defined in linker script or command
>> line?
> This is a good point. I missed this case.
> I have read the code a little bit.
>
> Multiple definition handling is broken for this case.
>
> the following command throws error about multiple definitions.
> ld --defsym foo=0x10 pr21703-1.o -o tmpdir/dump
>
> The command links fine, generating foo symbol with *MERGED* information from two definition.
> ld pr21703-1.o --defsym foo=0x10 -o tmpdir/dump
> 00000010     4 OBJECT  GLOBAL DEFAULT  ABS foo
>
> The functions to process symbol definitions from object file and command line is different.
> Multiple-definition is not handled for command line symbol definition. And the symbol
> value is overwritten by the symbol absolute value. The definition section is overwritten
> as well to ABS section.
>
> It's intended. Alan had a patch to allow multiple symbol definition without provide
> --allow-multiple-definition option.
> https://sourceware.org/ml/binutils/2014-12/msg00247.html
>
> The partial symbol information overwritten is the same problem as the original bug I
> reported.

So there is another question. What's the expected override behavior for command line, 
linker script and object/(static/dynamic)library defined symbols?

Is there a defined rule for those cases that I have missed?

Thanks!
Renlin.

>
>
> With or without the patch, the behavior remains the same.
> The symbol defined in command line option don't set h->def_regular flag.
> h->ldscript_def flag is set instead.
>
> Regards,
> Renlin
>