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 <return
type> 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
