RFR: JDK-8199608 Clean up LDFLAGS for libfontmanager (original) (raw)

Erik Joelsson erik.joelsson at oracle.com
Wed Mar 14 20:44:18 UTC 2018

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 libawtxawt or libawtheadless. 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 -lawtheadless 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 libawtheadless 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 libawtheadless 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. 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.

/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 libawtheadless. For macosx, this was libawtlwawt, 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 COMPAREBUILDS, 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 libawtheadless changed from e.g. "AWTCharAdvance" to "AWTCharAdvance@@SUNWprivate1.1". 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

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