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

Magnus Ihse Bursie magnus.ihse.bursie at oracle.com
Fri Mar 23 13:56:34 UTC 2018

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 $(EXPORT_ALL_SYMBOLS) to these libraries. Hopefully, we can remove this flag and fix proper exported symbols in the future.

I have run the complete build using COMPARE_BUILD, 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 __bss_start, _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 SUNWprivate_1.1 is not included, and thus neither the .gnu.version_d 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 do_foo() { ... }", but do_foo 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, do_foo() 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 libawt_xawt and libawt_headless, 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 jio_fprintf. (I have not listed the libjvm re-exports below.)

Note that  Java_java_io_FileOutputStream_close0 in java.base/unix/native/libjava/FileOutputStream_md.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: Java_java_io_FileOutputStream_close0 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.)  JLI_AddArgsFromEnvVar  JLI_CmdToArgs  JLI_GetAppArgIndex  JLI_GetStdArgc  JLI_GetStdArgs  JLI_InitArgProcessing  JLI_Launch  JLI_List_add  JLI_List_new  JLI_ManifestIterate  JLI_MemAlloc  JLI_MemFree  JLI_PreprocessArg  JLI_ReportErrorMessage  JLI_ReportErrorMessageSys  JLI_ReportExceptionDescription  JLI_ReportMessage  JLI_SetTraceLauncher  JLI_StringDup

java.desktop:/libawt_xawt: The following symbols are now also exported on linux and solaris due to JNIEXPORT:  awt_DrawingSurface_FreeDrawingSurfaceInfo  awt_DrawingSurface_GetDrawingSurfaceInfo  awt_DrawingSurface_Lock  awt_DrawingSurface_Unlock  awt_GetColor

The following symbols are now also exported on linux and solaris due to JNIEXPORT (they were previously  exported only in libawt):  Java_sun_awt_DebugSettings_setCTracingOn__Z  Java_sun_awt_DebugSettings_setCTracingOn__ZLjava_lang_String_2  Java_sun_awt_DebugSettings_setCTracingOn__ZLjava_lang_String_2I  Java_sun_awt_X11GraphicsConfig_getNumColors

java.desktop:/libawt_headless: The following symbols are now also exported due to JNIEXPORT (they were previously  exported only in libawt_xawt and/or libawt):  Java_sun_java2d_opengl_GLXGraphicsConfig_getGLXConfigInfo  Java_sun_java2d_opengl_GLXGraphicsConfig_getOGLCapabilities  Java_sun_java2d_x11_X11PMBlitLoops_updateBitmask  Java_sun_java2d_x11_X11SurfaceData_isShmPMAvailable  X11SurfaceData_GetOps

java.desktop/libawt: The following symbols are now also exported on Windows, due to added JNIEXPORT:  SurfaceData_InitOps  mul8table  div8table  doDrawPath  doFillPath  g_CMpDataID  initInverseGrayLut  make_dither_arrays  make_uns_ordered_dither_array  path2DFloatCoordsID  path2DNumTypesID  path2DTypesID  path2DWindingRuleID  sg2dStrokeHintID  std_img_oda_blue  std_img_oda_green  std_img_oda_red  std_odas_computed  sunHints_INTVAL_STROKE_PURE

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:  ByteGrayToIntArgbPreConvert_F  ByteGrayToIntArgbPreScaleConvert_F  IntArgbBmToFourByteAbgrPreScaleXparOver_F  IntArgbToIntRgbXorBlit_F  IntBgrToIntBgrAlphaMaskBlit_F

java.desktop/libawt on solaris: These are now also exported due to JNIEXPORT in libmlib_image.  j2d_mlib_ImageCreate  j2d_mlib_ImageCreateStruct  j2d_mlib_ImageDelete

java.desktop/libawt on solaris: This is now also exported due to JNIEXPORT:  GrPrim_CompGetXorColor  SurfaceData_GetOpsNoSetup  SurfaceData_IntersectBoundsXYWH  SurfaceData_SetOps  Transform_GetInfo  Transform_transform

java.desktop/libsplashscreen: JNI_OnLoad 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 libmlib_image .

jdk.sctp/libsctp: handleSocketError is now exported on linux and solaris due to JNIEXPORT in libnio.

java.instrument:/libinstrument: Agent_OnUnload is now also exported on linux and solaris platforms due to JNIEXPORT. JLI_ManifestIterate is now also exported on Windows, due to added JNIEXPORT in libjli.

jdk.management/libmanagement_ext: Java_com_sun_management_internal_Flag_setDoubleValue is now also exported on linux and solaris platforms due to JNIEXPORT.

/Magnus

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