RFR: JDK-8200178 Remove mapfiles for JDK native libraries (original) (raw)

Volker Simonis volker.simonis at gmail.com
Fri Mar 23 17:24:24 UTC 2018

Hi Magnus,

thanks for addressing this long standing issue! I haven't looked at the changes, but just want to share some general and historical notes:

Then we had several mail threads (which you probably remember because you were involved :) where we discussed to either remove the map files completely or instead generate them automatically during the build:

http://mail.openjdk.java.net/pipermail/hotspot-dev/2014-February/thread.html#12412 http://mail.openjdk.java.net/pipermail/hotspot-dev/2014-February/thread.html#12628

The main arguments against removing the map files at that time were:

  1. the danger to re-export all symbols of statically linked libraries (notably libstdc++ at that time)
  2. loosing exports of compiler generated symbols like vtables which are required by the Serviceability Agent

Point 1 is not a problem today, because I don't think we do any static linking any more. If we still do it under some circumstances, this problem should be re-evaluated.

Point 2 is only relevant for HotSpot. But because of "8034065: GCC 4.3 and later doesn't export vtable symbols any more which seem to be needed by SA" (https://bugs.openjdk.java.net/browse/JDK-8034065), exporting such symbols trough a map files doesn't work any more anyway. So this isn't a problem either.

So to cut a long story short - I think the time is ripe to get rid of the map files. Thumbs up from me (meant as moral support, not as a concrete review :)

Regards, Volker

On Fri, Mar 23, 2018 at 5:05 PM, mandy chung <mandy.chung at oracle.com> wrote:

This is a very good change and no more mapfile to maintain!!

Please do file JBS issues for the component teams to clean up their exports. Mandy

On 3/23/18 7:30 AM, Erik Joelsson wrote:

I have looked at the build changes and they look good. Will you file followups for each component team to look over their exported symbols, at least for the libraries with $(EXPORTALLSYMBOLS)? It sure looks like there is some technical debt laying around here. /Erik

On 2018-03-23 06:56, Magnus Ihse Bursie wrote: With modern compilers, we can use compiler directives (such as attribute((visibility("default"))), or declspec(dllexport)) to control symbol visibility, directly in the source code. This has historically not been present on all compilers, so we had to resort to using mapfiles (also known as linker scripts). This is no longer the case. Now all compilers we use support symbol visibility directives, in one form or another. We should start using this. Since this has been the only way to control symbol visibility on Windows, for most of the shared code, we already have proper JNIEXPORT decorations in place. If we fix the remaining platform-specific files to have proper JNIEXPORT tagging, then we can finally get rid of mapfiles. This fix removed mapfiles for all JDK libraries. It does not touch hotspot libraries nor JDK executables; they will have to wait for a future fix -- this was complex enough. This change will not have any impact on macosx, since we do not use mapfiles there, but instead export all symbols. (This is not a good idea, but I'll address that separately.) This change will also have a minimal impact on Windows. The only reason Windows is impacted at all, is that some changes needed by Solaris and Linux were simpler to fix for all platforms. I have strived for this change to have no impact on the actual generated code. Unfortunately, this was not possible to fully achieve. I do not believe that these changes will have any actual impact on the product, though. I will present the differences more in detail further down. Those who are not interested can probably skip that. The patch has passed tier1 testing and is currently running tier2 and tier3. Since the running code is more or less (see caveat below) unmodified, I don't expect any testing issues. Bug: https://bugs.openjdk.java.net/browse/JDK-8200178 WebRev: http://cr.openjdk.java.net/~ihse/JDK-8200178-remove-mapfiles/webrev.01 Details on changes: Most of the source code changes are (unsurprisingly) in java.base and java.desktop. Remaining changes are in jdk.crypto.ucrypto, jdk.hotspot.agent, jdk.jdi and jdk.jdwp.agent. Source code changes does almost to 100% consists in decorating an exported function with JNIEXPORT. I have also followed the long-standing convention of adding JNICALL. This is a no-op on non-Windows platforms, so for most of the changes this is purely cosmetic (and possibly adding in robustness, should the function ever be used on Windows in the future). I have also followed the stylistic convention of putting "JNIEXPORT JNICALL" on a separate line. For some functions, however, this might cause a change in calling convention on Windows. Since this can not apply to exported functions on Windows (otherwise they would already have had JNIEXPORT), I do not think this matters anything. A few libraries did not have a mapfile, on Linux and/or Solaris. This actually meant that all symbols were exported. It is highly unclear if this was known and intended by the original make rule writer. I have emulated this by adding the flag $(EXPORTALLSYMBOLS) to these libraries. Hopefully, we can remove this flag and fix proper exported symbols in the future. I have run the complete build using COMPAREBUILD, and made a thourough analysis of the differences for Linux and Solaris. All native libraries have symbol differences, but most of them are trivial and/or harmless. As a result, most libraries have disasm differences as well, but these too seem trivial and harmless. The differences in symbols that are common to all libraries include: _* Internal symbols such as bssstart, edata, end and fini are now global. (They are imported as such from the compiler libraries/archives, and we have no linker script to override this behavior). * The versioning tag SUNWprivate1.1 is not included, and thus neither the .gnu.versiond symbol. * There are a few differences in the symbol and/or mangling of some local functions. I'm not sure what's causing this, but it's unlikely to have any effect on the product. Another common source for change in symbols is due to previous platform differences. For instance, if we had "JNIEXPORT int JNICALL dofoo() { ... }", but dofoo was not in the mapfile, the symbol was exported on Windows but not on Linux and Solaris. (Presumable since it was not needed there, even though it was compiled for those platforms as well.) Now, with the mapfiles gone, dofoo() will be exported on all platforms. And contrary, functions that are compiled on all platforms, and were exported in mapfiles, but now have gotten an JNIEXPORT decoration, will now be visible even on Windows. (This accounts for half of the noticed symbol differences on Windows.) I could have made the JNIEXPORT conditional on OS, but I didn't think the mess in source code were worth the keeping of binary confidence with the old build. A third common source for change in symbols is due to exported functions "leaking" across library borders. For instance, some functions in java.desktop is compiled in both libawtxawt and libawtheadless, but they were previously only included in the mapfile for one of these libraries. Now, since the visibility is determined by the source code itself, it gets exported in both libraries. A variant of this is when a library depends on another JDK library, and includes the header file from that other library, which in turn declares a function as JNIEXPORT. This will cause the including library to also export the function. This accounts for the other half of the changes on Windows. A typical example of this is that multiple libraries now re-export hotspot symbols from libjvm.so, like jiofprintf. (I have not listed the libjvm re-exports below.) Note that JavajavaioFileOutputStreamclose0 in java.base/unix/native/libjava/FileOutputStreammd.c is no longer exported, and can probably be removed. Here is a detailed table showing and accounting for all the remaining differences found on Linux and Solaris: java.base/unix/native/libjava: JavajavaioFileOutputStreamclose0 is now also exported on unix platforms due to JNIEXPORT. java.base/jspawnlauncher: On solaris, we also include libjava/childproc.o, which now exports less functions than it used to (it used to export all functions, now it is compiled with visibility=hidden). java.base/java(w).exe: Is now also exporting the following symbols due to added JNIEXPORT in libjli on Windows: (Yes, executables can export symbols on Windows. Confusing, I know.) JLIAddArgsFromEnvVar JLICmdToArgs JLIGetAppArgIndex JLIGetStdArgc JLIGetStdArgs JLIInitArgProcessing JLILaunch JLIListadd JLIListnew JLIManifestIterate JLIMemAlloc JLIMemFree JLIPreprocessArg JLIReportErrorMessage JLIReportErrorMessageSys JLIReportExceptionDescription JLIReportMessage JLISetTraceLauncher JLIStringDup java.desktop:/libawtxawt: The following symbols are now also exported on linux and solaris due to JNIEXPORT: awtDrawingSurfaceFreeDrawingSurfaceInfo awtDrawingSurfaceGetDrawingSurfaceInfo awtDrawingSurfaceLock awtDrawingSurfaceUnlock awtGetColor The following symbols are now also exported on linux and solaris due to JNIEXPORT (they were previously exported only in libawt): JavasunawtDebugSettingssetCTracingOn_Z JavasunawtDebugSettingssetCTracingOn_ZLjavalangString2 JavasunawtDebugSettingssetCTracingOn_ZLjavalangString2I JavasunawtX11GraphicsConfiggetNumColors java.desktop:/libawtheadless: The following symbols are now also exported due to JNIEXPORT (they were previously exported only in libawtxawt and/or libawt): Javasunjava2dopenglGLXGraphicsConfiggetGLXConfigInfo Javasunjava2dopenglGLXGraphicsConfiggetOGLCapabilities Javasunjava2dx11X11PMBlitLoopsupdateBitmask Javasunjava2dx11X11SurfaceDataisShmPMAvailable X11SurfaceDataGetOps java.desktop/libawt: The following symbols are now also exported on Windows, due to added JNIEXPORT: SurfaceDataInitOps mul8table div8table doDrawPath doFillPath gCMpDataID initInverseGrayLut makeditherarrays makeunsorderedditherarray path2DFloatCoordsID path2DNumTypesID path2DTypesID path2DWindingRuleID sg2dStrokeHintID stdimgodablue stdimgodagreen stdimgodared stdodascomputed sunHintsINTVALSTROKEPURE java.desktop/libawt on solaris: A number of "#pragma weak" directives was previously overridden by the mapfile. Now these directives are respected, so these symbols are now weak instead of local: ByteGrayToIntArgbPreConvertF ByteGrayToIntArgbPreScaleConvertF IntArgbBmToFourByteAbgrPreScaleXparOverF IntArgbToIntRgbXorBlitF IntBgrToIntBgrAlphaMaskBlitF java.desktop/libawt on solaris: These are now also exported due to JNIEXPORT in libmlibimage. j2dmlibImageCreate j2dmlibImageCreateStruct j2dmlibImageDelete java.desktop/libawt on solaris: This is now also exported due to JNIEXPORT: GrPrimCompGetXorColor SurfaceDataGetOpsNoSetup SurfaceDataIntersectBoundsXYWH SurfaceDataSetOps TransformGetInfo Transformtransform java.desktop/libsplashscreen: JNIOnLoad is now exported on linux and solaris due to JNIEXPORT. libspashscreen also had JNIEXPORT (actually a pure declspec(dllexport)) but no JNICALL, which I added as a part of converting to JNIEXPORT. The same goes for libmlibimage . jdk.sctp/libsctp: handleSocketError is now exported on linux and solaris due to JNIEXPORT in libnio. java.instrument:/libinstrument: AgentOnUnload is now also exported on linux and solaris platforms due to JNIEXPORT. JLIManifestIterate is now also exported on Windows, due to added JNIEXPORT in libjli. jdk.management/libmanagementext: JavacomsunmanagementinternalFlagsetDoubleValue is now also exported on linux and solaris platforms due to JNIEXPORT. /Magnus

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