RFR: JDK-8199608 Clean up LDFLAGS for libfontmanager

[Magnus Ihse Bursie]

On 2018-03-14 21:44, Erik Joelsson wrote:
> On 2018-03-14 13:22, Magnus Ihse Bursie wrote:
>> On 2018-03-14 15:59, Erik Joelsson wrote:
>>> This change is unfortunately not correct for Linux and Solaris. We 
>>> cannot link libfontmanager explicitly against either libawt_xawt or 
>>> libawt_headless. See 
>>> https://bugs.openjdk.java.net/browse/JDK-8196516 for my suggestion 
>>> on a better fix than we currently have. I was hoping for Severin to 
>>> check it out and pick it up, but he is away for a bit so that hasn't 
>>> happened.
>>>
>>> The reason we cannot link explicitly is that we need to decide at 
>>> runtime whether to pull in the headful or headless libraries. If one 
>>> or the other is already pulled in, and we explicitly load the other, 
>>> the runtime linker will lookup the common symbols in one or the 
>>> other in an unpredictable way. Some users get the correct behavior, 
>>> some get the wrong behavior. We recently had discussions around this 
>>> on this list if you want to dive deeper into it.
>>>
>>> Also see https://bugs.openjdk.java.net/browse/JDK-8194870 for one of 
>>> the consequences of explicit linking here.
>>>
>>> I think the mac part is ok though, but Phil has to have a look. For 
>>> Linux and Solaris, if you could remove the -lawt_headless and add 
>>> "-Xlinker --unresolved-symbols=ignore-all" to LDFLAGS for linux I 
>>> think we should be good.
>> Oh, this seems like a fine mess. :-(
>>
>> I see we used to link with libawt_headless for solaris, but removed 
>> it in JDK-8194870. Phil remarked in that bug: "We linked against 
>> headless before then but allowed undefined symbols JDK 9 switched 
>> this to libawt_headless when headless apps failed." but I'm not sure 
>> I understand what this really means.
> I think he means that we linked with xawt before, but switch to 
> headless at some point. If you run on a machine without X11 present, 
> then if you load xawt, you get a runtime linker error. That was the 
> reason for switching to linking with headless instead.
>>
>> I agree it seems likely that the macosx changes is correct. I could 
>> probably add -Wl,--unresolved-symbols=ignore-all for gcc on linux, 
>> but that is unlikely to work on solstudio. :-( So I'm afraid we're 
>> still stuck with the need to remove -z defs for some builds. :-(
>>
> On solaris we should be able to override -Wl,-z,defs with 
> -Wl,-z,nodefs later on the link line I think. 
Unfortunately, that gives the error "-z defs and -z nodefs are mutually 
exclusive", or something like that. :-(

> Perhaps that works on Linux as well. I didn't find nodefs on the Linux 
> man page, but coming to think about it, the "no" prefix should be 
> universal.
>> Question to Phil: Would it be possible to rewrite the code to load 
>> and reference the symbols dynamically, using libdl? The problem here 
>> is that the functions are declared extern, instead of loaded into a 
>> function pointer at runtime. That's how you typically use this kind 
>> of runtime-determined dynamic loading.
>>
> That sounds like a better long term solution.
The problem here is the "long" in "long term". :-( What I'm trying to 
accomplish here is to make sure that all JDK libraries use the 
LDFLAGS_JDKLIB for linking (and possibly additional flags), not a 
version with some parts subst:ed out. :(

I can't really find a way to accomplish this for solstudio short of 
fixing this to use proper dynamic linking.

/Magnus
>
> /Erik
>> /Magnus
>>>
>>> /Erik
>>>
>>> On 2018-03-14 04:45, Magnus Ihse Bursie wrote:
>>>> This is the final LDFLAGS cleanup, which required some more work to 
>>>> resolve.
>>>>
>>>> Libfontmanager had previously explicitely disabled -z defs, with 
>>>> the result that linking did not complain about missing libraries. 
>>>> To fix this, I had to provide the proper libraries to link with. 
>>>> For linux and solaris, this was libawt_headless. For macosx, this 
>>>> was libawt_lwawt, but also three system frameworks.
>>>>
>>>> Note that this patch has a merge conflict with JDK-8199606. The end 
>>>> result of both patches are shown in the patch (that is, with -lc 
>>>> removed). I will make sure to resolve the conflicts properly when 
>>>> committing this patch.
>>>>
>>>> I have run COMPARE_BUILDS, with expected results. That is, no 
>>>> changes for Windows, and a deps change for macosx, linux and 
>>>> solaris. I also got a symbol change for linux, since the symbols 
>>>> from libawt_headless changed from e.g. "AWTCharAdvance" to 
>>>> "AWTCharAdvance@@SUNWprivate_1.1". And of course, when you do 
>>>> linking changes, you also end up getting binary/disasm changes.
>>>>
>>>> Bug: https://bugs.openjdk.java.net/browse/JDK-8199608
>>>> WebRev: 
>>>> http://cr.openjdk.java.net/~ihse/JDK-8199608-clean-up-LDFLAGS-for-libfontmanager/webrev.01
>>>>
>>>
>>
>