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

[Renlin Li]

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.


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