Why do we need both - export maps AND -fvisibility=hidden/__attribute__((visibility("default")))

[Staffan Larsen]

Good that you are looking at it.

My comment was on map-files. The static map files we have today aren’t involved with creating vtable symbols.

/Staffan

On 17 feb 2014, at 09:18, Dmitry Samersoff <dmitry.samersoff at oracle.com> wrote:

> Staffan,
> 
> I'd dived into this problem last week.
> 
> SA uses address of vtable (_ZTV* symbols) to calculate base addresses
> for couple of internal structures.
> 
> i.e. (roughly) it takes vtable address, add offset from vm_structs and
> get the data.
> 
> Since the time when hotspot build switched to gcc 4.x it doesn't work,
> so many of SA command (e.g. jdis) is broken now.
> 
> I'm looking for solution.
> 
> see
> https://bugs.openjdk.java.net/browse/JDK-8034065
> 
> -Dmitry
> 
> 
> On 2014-02-17 11:50, Staffan Larsen wrote:
>> 
>> On 17 feb 2014, at 03:15, David Holmes <david.holmes at oracle.com> wrote:
>> 
>>> On 13/02/2014 5:26 PM, Magnus Ihse Bursie wrote:
>>>> 
>>>> On 2014-02-05 19:09, Volker Simonis wrote:
>>>>> If there are any more/other comments on this topic I'll be highly
>>>>> interested.
>>>> 
>>>> You can count on me having lots of opinion on build issues. ;-)
>>>> 
>>>> I'd like to get rid of the hard-coded map files completely, both in
>>>> hotspot and jdk. This can be done without loss of functionality. How?
>>>> Because we can generate them on the fly at build time, using information
>>>> provided by the source code.
>>> 
>>> Does that account for the dynamically generated symbols used by the SA?
>> 
>> I think the symbols SA care about are all already declared with JNIEXPORT.
>> 
>> /Staffan
>> 
>>> 
>>> David
>>> 
>>>> Note that the exported functions are prefixed by the macro JNIEXPORT. We
>>>> can locate all functions that have this prefix and write them to a map
>>>> file. This can be done, and was indeed the way we solved things back in
>>>> the JRockit JVM. The technique we used there was to grep for "JNIEXPORT"
>>>> and check for a symbol name (as provided by nm). We had rules requiring
>>>> that JNIEXPORT was to be written on the same line as the function name,
>>>> or the line before that. So we could do like "grep -A 1 -e JNIEXPORT"
>>>> and then cross-reference for names extracted by nm. Not exactly a formal
>>>> semantic parsing, but it was efficient and worked very well. I believe
>>>> we can do something very similar for hotspot and jdk.
>>>> 
>>>> Then again, if we could get rid of maps completely, by using visibility
>>>> and not linking statically with the standard libs, that would be even
>>>> better. :-)
>>>> 
>>>> /Magnus
>> 
> 
> 
> -- 
> Dmitry Samersoff
> Oracle Java development team, Saint Petersburg, Russia
> * I would love to change the world, but they won't give me the sources.