Why does java app crash in gdb but runs normally i

Question

Attempting to run java app from gdb results in segfault, yet running app alone does not. This app is a .JAR which uses JOGL and a bit of memory-mapping to talk to the GPU.

Stacktrace below hints at some sort of memory access problem but I don't understand why it manifests in GDB but not in real life. Could there be some environment factor gdb needs to know to allow proper execution?

This issue persists between JVMs OpenJDK 6 and 7, as well as Oracle JRE 7. The oracle JRE runs a little farther into startup before segfault. All segfaults are otherwise consistent in occurrence and location between trials.

Segfault persists between GPUs and drivers(!!): nvidia, radeon, fglrx current and fglrx beta (14.xx). GDB will successfully attach to an already-running instance of my program, however it doesn't seem possible for gDEBugger to do this, which is ultimately what needs to work.

There is no intent to actually debug with gdb. Rather I am trying to use gDEBugger to perform OpenGL debugging. gDEBugger apparently relies on GDB as part of its backend, so if GDB fails, so does gDEBugger. This resulted in attempts to run gdb alone to isolate the issue.

gDEBugger output:
GDB String:  [Thread debugging using libthread_db enabled]  
GDB String:  Using host libthread_db library  /lib/x86_64-linux-gnu/libthread_db.so.1 .  
Thread Created: 140737353893632 (LWP: 3265)
Thread Created: 140737294624512 (LWP: 3266)
Thread Created: 140737293571840 (LWP: 3267)
Thread Created: 140737292519168 (LWP: 3268)
Thread Created: 140737155180288 (LWP: 3269)
Thread Created: 140737154127616 (LWP: 3270)
Thread Created: 140736913602304 (LWP: 3271)
Thread Created: 140736909629184 (LWP: 3272)
Thread Created: 140736908576512 (LWP: 3273)
Thread Created: 140736907523840 (LWP: 3274)
Thread Created: 140736906471168 (LWP: 3275)
Thread Created: 140736905418496 (LWP: 3276)
Thread Created: 140736278275840 (LWP: 3277)
Thread Created: 140736272963328 (LWP: 3278)
Thread Created: 140736271910656 (LWP: 3279)
Thread Created: 140736270857984 (LWP: 3280)
Thread Created: 140736269805312 (LWP: 3281)
Thread Created: 140737287657216 (LWP: 3285)
Thread Created: 140736261945088 (LWP: 3289)
GDB String:  [Thread 0x7fffb6e67700 (LWP 3289) exited]  
Thread Created: 140736261945088 (LWP: 3290)
API Connection Established: gDEBugger Servers Manager
Thread Created: 140736234641152 (LWP: 3291)
GDB String:  [Thread 0x7fffb6e67700 (LWP 3290) exited]  
API Connection Established: gDEBugger OpenGL Server
GDB String:  [Thread 0x7fffb77e8700 (LWP 3279) exited]  
GDB String:  [Thread 0x7fffb76e7700 (LWP 3280) exited]  
Debug String: gDEBugger OpenGL Server was initialized
Thread Created: 140736270857984 (LWP: 3292)
Thread Created: 140735692441344 (LWP: 3294)
Thread Created: 140735582430976 (LWP: 3295)
Thread Created: 140735574038272 (LWP: 3296)
OpenGL Render Context 1 Created
Signal: SIGSEGV
Process Exit


$ java -versionjava version "1.6.0_33"
OpenJDK Runtime Environment (IcedTea6 1.13.5) (6b33-1.13.5-1ubuntu0.14.04)
OpenJDK 64-Bit Server VM (build 23.25-b01, mixed mode)

$ gdb -version
GNU gdb (Ubuntu 7.7.1-0ubuntu5~14.04.2) 7.7.1

$ cat /etc/lsb-release
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=14.04
DISTRIB_CODENAME=trusty
DISTRIB_DESCRIPTION="Ubuntu 14.04.1 LTS"

$ fglrxinfo
display: :0.0  screen: 0
OpenGL vendor string: Advanced Micro Devices, Inc.
OpenGL renderer string: AMD Radeon HD 5570     
OpenGL version string: 4.4.12967 Compatibility Profile Context 14.20


$ gdb --args java -jar RunMe.jar
GNU gdb (Ubuntu 7.7.1-0ubuntu5~14.04.2) 7.7.1
Copyright (C) 2014 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-linux-gnu".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from java...Reading symbols from /usr/lib/debug//usr/lib/jvm/java-6-openjdk-amd64/jre/bin/java...done.
done.
(gdb) show configuration
This GDB was configured as follows:
   configure --host=x86_64-linux-gnu --target=x86_64-linux-gnu
             --with-auto-load-dir=$debugdir:$datadir/auto-load
             --with-auto-load-safe-path=$debugdir:$datadir/auto-load
             --with-expat
             --with-gdb-datadir=/usr/share/gdb (relocatable)
             --with-jit-reader-dir=/usr/lib/gdb (relocatable)
             --without-libunwind-ia64
             --with-lzma
             --with-python=/usr (relocatable)
             --with-separate-debug-dir=/usr/lib/debug (relocatable)
             --with-system-gdbinit=/etc/gdb/gdbinit
             --with-zlib
             --without-babeltrace
(gdb) run
Starting program: /usr/bin/java -jar RunMe.jar
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
process 6866 is executing new program: /usr/lib/jvm/java-6-openjdk-amd64/jre/bin/java
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
[New Thread 0x7ffff7fc4700 (LWP 6870)]
[New Thread 0x7ffff486c700 (LWP 6871)]
[New Thread 0x7ffff476b700 (LWP 6872)]
[New Thread 0x7ffff466a700 (LWP 6873)]
[New Thread 0x7fffea2d6700 (LWP 6874)]
[New Thread 0x7fffea1d5700 (LWP 6875)]
[New Thread 0x7fffea0d4700 (LWP 6876)]
[New Thread 0x7fffe9d0a700 (LWP 6877)]
[New Thread 0x7fffe9c09700 (LWP 6878)]
[New Thread 0x7fffe9b08700 (LWP 6879)]
[New Thread 0x7fffe9a07700 (LWP 6880)]
[New Thread 0x7fffe9906700 (LWP 6881)]
...
[New Thread 0x7fffe8110700 (LWP 6882)]
[New Thread 0x7fffe3169700 (LWP 6883)]
[New Thread 0x7fffe3068700 (LWP 6884)]
[New Thread 0x7fffe2f67700 (LWP 6885)]
[New Thread 0x7fffe2e66700 (LWP 6886)]
[New Thread 0x7fffe2d65700 (LWP 6887)]
[Thread 0x7fffe2d65700 (LWP 6887) exited]
[New Thread 0x7fffe2d65700 (LWP 6891)]
[Thread 0x7fffe2d65700 (LWP 6891) exited]
[New Thread 0x7fffe2d65700 (LWP 6895)]
[Thread 0x7fffe2d65700 (LWP 6895) exited]
[New Thread 0x7fffe2d65700 (LWP 6896)]
[New Thread 0x7fffe0efd700 (LWP 6897)]
libEGL warning: DRI2: failed to authenticate
[New Thread 0x7fff9799f700 (LWP 6898)]
[New Thread 0x7fff9719e700 (LWP 6899)]
[New Thread 0x7fff9699d700 (LWP 6900)]
[Thread 0x7fffe2d65700 (LWP 6896) exited]
[New Thread 0x7fffe2d65700 (LWP 6901)]
[New Thread 0x7fffe01ab700 (LWP 6902)]
[New Thread 0x7fff92f00700 (LWP 6903)]
[New Thread 0x7fff92dff700 (LWP 6904)]
[New Thread 0x7fff92cfe700 (LWP 6905)]
Setting up sound system...[New Thread 0x7fff92bfd700 (LWP 6906)]

[New Thread 0x7fff92afc700 (LWP 6907)]
[New Thread 0x7fff929fb700 (LWP 6908)]
[New Thread 0x7fff928fa700 (LWP 6909)]
[New Thread 0x7fff927f9700 (LWP 6910)]
[New Thread 0x7fff926f8700 (LWP 6911)]
[New Thread 0x7fff925f7700 (LWP 6912)]

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x7fffe2f67700 (LWP 6885)]
0x00007ffff6b3a770 in acl_CopyRight ()
   from /usr/lib/jvm/java-6-openjdk-amd64/jre/lib/amd64/server/libjvm.so
(gdb) where
#0  0x00007ffff6b3a770 in acl_CopyRight ()
   from /usr/lib/jvm/java-6-openjdk-amd64/jre/lib/amd64/server/libjvm.so
#1  0x00007ffff6d51309 in Unsafe_CopyMemory2 (env=<optimized out>, 
    unsafe=<optimized out>, srcObj=0x0, srcOffset=140737008618496, dstObj=0x0, 
    dstOffset=140737006779392, size=1024)
    at /build/buildd/openjdk-6-6b33-1.13.5/build/openjdk/hotspot/src/share/vm/prims/unsafe.cpp:689
#2  0x00007fffed011790 in ?? ()
#3  0x0000000000000400 in ?? ()
#4  0x0000000000000000 in ?? ()
Warning: the current language does not match this frame.
(gdb) quit
A debugging session is active.

    Inferior 1 [process 6866] will be killed.

Quit anyway? (y or n) y

UPDATE: Switched to AMD CodeXL (basically the most recent form of gDEBugger) and situation hasn't changed much.

Answer 1

Why does java app crash in gdb but runs normally in real life?

Because it doesn't actually crash.

Java uses speculative loads. If a pointer points to addressable memory, the load succeeds. Rarely the pointer does not point to addressable memory, and the attempted load generates SIGSEGV ... which java runtime intercepts, makes the memory addressable again, and restarts the load instruction.

When debugging java programs, one has to generally do this:

(gdb) handle SIGSEGV nostop noprint pass

Unfortunately, if there is some JNI code involved, and that code SIGSEGVs, GDB will happily ignore that signal as well, resulting in the death of inferior (being debugged) process. I have not found an acceptable solution for that latter problem.