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

[Fangrui Song]

On 2020-05-23, Fangrui Song wrote:
>On 2020-05-23, H.J. Lu wrote:
>>On Fri, May 22, 2020 at 8:56 AM Fangrui Song <maskray@google.com> wrote:
>>>
>>>
>>>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.
>>
>>There is no need to change linker manual.  --dynamic-list* should work both
>>before and after -Bsymbolic and -Bsymbolic-functions.  Your patch used
>>libdl2d.so without creating it first.
>>
>>Here is the updated version of your patch.  I took the liberty to make
>>the changes above.
>>
>>-- 
>>H.J.
>
>Thanks for the fix (libdl4e.so->libdl2d.so)
>
>The updated patch looks good to me.

Around lexsup.c:1162

`case symbolic_functions:` should set link_info.dynamic_data and link_info.dynamic , otherwise
-Bsymbolic-functions is broken.


.globl _start, foo
_start:
   call foo
foo

ld-new -shared -Bsymbolic-functions a.o -o a.so

foo@plt is not created