[PATCH] ld: Make --dynamic-list* override -Bsymbolic -Bsymbolic-functions

[Fangrui Song]

On 2020-05-22, H.J. Lu wrote:
>On Wed, May 20, 2020 at 6:48 PM Fangrui Song via Binutils
><binutils@sourceware.org> wrote:
>>
>> They aren't used together in reality, so it is safe to change the
>> semantics. --dynamic-list is refined -Bsymbolic. -Bsymbolic-functions
>> should be considered as a subset of -Bsymbolic, so --dynamic-list
>> overridding -Bsymbolic implies that --dynamic-list overridding
>> -Bsymbolic-functions.
>
>--dynamic-list=DYNAMIC-LIST-FILE'
>     Specify the name of a dynamic list file to the linker.  This is
>     typically used when creating shared libraries to specify a list of
>     global symbols whose references shouldn't be bound to the
>     definition within the shared library, or creating dynamically
>     linked executables to specify a list of symbols which should be
>     added to the symbol table in the executable.  This option is only
>     meaningful on ELF platforms which support shared libraries.
>
>The --dynamic-list* options are intended for shared libraries. 

--dynamic-list* work for both executables and shared libraries.
For an executable, export some symbols.
For a shared library, specify preemptible symbols.

>The goal
>IS NOT put them in dynamic symbol table since all global symbols are in
>dynamic symbol table already in a shared library.  The goal is to make
>them PREEMPTIBLE.  

I agree with this sentence and the patch respects it.

>So making the --dynamic-list* options override -Bsymbolic
>and -Bsymbolic-functions is incorrect since there is NOTHING to override.

I don't agree with this statement. --dynamic-list* have function overlay
with -Bsymbolic. When two options overlap in functionality, many users
expect the more fine-grained option to win, thus my thought that
--dynamic-list* override -Bsymbolic and -Bsymbolic-functions.

(FWIW LLD's preemptibility logic is
   ...
   if (config->hasDynamicList)
     return sym.inDynamicList;
   return !(config->bsymbolic || config->bsymbolicFunctions && sym.isFunc());
   This works fine and I won't change it.
)

>To do it properly:
>
>1.  Extend  --dynamic-list* to executables.  Symbol binding is unchanged.
>Only add symbols to dynamic symbol table.

This was already implemented when you implemented --dynamic-list in
2006. This patch does not change the fact.

>2. Make --export-dynamic-symbol an alias of  --dynamic-list* for executables.
>and ignore --export-dynamic-symbol for -shared.  It has to be done at the
>end of command-line parsing.

I am happy with the description about --export-dynamic-symbol.

>> This also helps PR ld/25910, which would make the situation more
>> difficult to understand.
>>
>>         PR ld/26018
>>         * lexsup.c: Simplify.
>>         * ld.texi: Update documentation.
>>         * testsuite/ld-elf/shared.exp: Update tests.
>>         * testsuite/ld-elf/dl4e.out: New.
>
>
>
>-- 
>H.J.