Segv in malloc

I was running Java Workshop on JDK 1.1 and using it to debug
another instance of Java Workshop when the debuggee VM segv'd.
I have moved the core file to ~/cores/core-java.4. Here is
the dbx stack trace:

(dbx) w
=>[1] strlen(0x0, 0xf5eb8050, 0x1, 0x7efefeff, 0x81010100, 0xef51353c), at 0xef4a3db0
  [2] format_string(0xef04f9d0, 0xf5eb8050, 0x1, 0x0, 0x3ff, 0x3ff), at 0xef750a08
  [3] jio_vsnprintf(0xef51176d, 0x5e, 0xef772e84, 0xef04fa88, 0xef78dc68, 0xef772e86), at 0xef7514f4
  [4] jio_snprintf(0xef78dc68, 0x400, 0xef772e84, 0xf5eb8050, 0xedcf038c, 0xef04fe20), at 0xef751740
  [5] decode_si_code(0xb, 0xef04fe20, 0xef78d510, 0x2, 0x0, 0x0), at 0xef766134
  [6] signalHandlerPanic(0xef04fe20, 0xef513a38, 0xef04fc60, 0xb, 0x0, 0x10000), at 0xef766414
  ---- called from signal handler with signal 11 (SIGSEGV) ------
  [7] realfree(), at 0xef4cb92c
  [8] _malloc_unlocked(0x60, 0x2, 0xedbf0274, 0x1000a8, 0x333b2037, 0xedbf02dc), at 0xef4cb494
  [9] malloc(0x60, 0x2894e, 0x333b2037, 0x28927, 0x12, 0x0), at 0xef4cb214
  [10] awt_copyXEvent(0xef0501c0, 0xef181290, 0x0, 0x170aa0, 0x176fa8, 0xef10c374), at 0xef180bd8
  [11] awt_canvas_handleEvent(0xef199800, 0xee2fb240, 0xef0501c0, 0x6839c0, 0xef05015f, 0x1), at 0xef18190c
  [12] dispatchToWidget(0xef0501c0, 0xef0501c0, 0x746748, 0x19a560, 0x0, 0x1), at 0xef1657ac
  [13] awt_MToolkit_loop(0x1, 0xef1a56b4, 0xef199440, 0xef1a5634, 0xef165400, 0x0), at 0xef165904
  [14] sun_awt_motif_MToolkit_run(0xef1a56b4, 0xef199450, 0xef784bec, 0x18, 0x3, 0x3b8c25), at 0xef1659c8
  [15] Java_sun_awt_motif_MToolkit_run_stub(0x1c90d8, 0xef050ca4, 0xee300000, 0xef050ca4, 0xef050bb4, 0xef050bbc), at 0xef184250
  [16] invokeNativeMethod(0x1c90d8, 0x1c0860, 0x1, 0xef050ca4, 0x1c90b0, 0xef78e400), at 0xef71f370
  [17] ExecuteJava(0xef050cb4, 0xef050ca4, 0x1c90d4, 0x1c90d8, 0x61ec3, 0x1c90b0), at 0xef76244c
  [18] do_execute_java_method_vararg(0xef050ca4, 0xef78a605, 0x0, 0x0, 0x0, 0x1c9070), at 0xef72ef4c
  [19] execute_java_dynamic_method(0xef050ca4, 0xee309400, 0xef78a600, 0xef78a604, 0xef78d800, 0xf5fbccd0), at 0xef72e58c
  [20] ThreadRT0(0xee309400, 0xef78a604, 0x22cd8, 0xef080de0, 0x3bb7a909, 0x9), at 0xef74ed78
  [21] start_func(0xef772c00, 0xee309400, 0xef74ecf4, 0x0, 0x0, 0x0), at 0xef76dba8
(dbx)