void ustack(int nframes, int strsize) void ustack(int nframes) void ustack(void)
The ustack action records a user stack trace to the directed buffer. The user stack will be nframes in depth. If nframes is not provided, the number of stack frames recorded is the number specified by the ustackframes option. While ustack is able to determine the address of the calling frames when the probe fires, the stack frames will not be translated into symbols until the ustack action is processed at user-level by the DTrace consumer. If strsize is specified and non-zero, ustack will allocate the specified amount of string space, and use it to perform address-to-symbol translation directly from the kernel. This direct user symbol translation is currently available only for Java virtual machines, version 1.5 and higher. Java address-to-symbol translation annotates user stacks that contain Java frames with the Java class and method name. If such frames cannot be translated, the frames will appear only as hexadecimal addresses.
The following example traces a stack with no string space, and therefore no Java address-to-symbol translation:
# dtrace -n syscall::write:entry'/pid == $target/{ustack(50, 0); exit(0)}' -c "java -version" dtrace: description 'syscall::write:entry' matched 1 probe java version "1.5.0-beta3" Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0-beta3-b58) Java HotSpot(TM) Client VM (build 1.5.0-beta3-b58, mixed mode) dtrace: pid 5312 has exited CPU ID FUNCTION:NAME 0 35 write:entry libc.so.1`_write+0x15 libjvm.so`__1cDhpiFwrite6FipkvI_I_+0xa8 libjvm.so`JVM_Write+0x2f d0c5c946 libjava.so`Java_java_io_FileOutputStream_writeBytes+0x2c cb007fcd cb002a7b cb002a7b cb002a7b cb002a7b cb002a7b cb002a7b cb002a7b cb002a7b cb002a7b cb002a7b cb002a7b cb002a7b cb002a7b cb000152 libjvm.so`__1cJJavaCallsLcall_helper6FpnJJavaValue_ pnMmethodHandle_pnRJavaCallArguments_ pnGThread__v_+0x187 libjvm.so`__1cCosUos_exception_wrapper6FpFpnJJavaValue_ pnMmethodHandle_pnRJavaCallArguments_ pnGThread__v2468_v_+0x14 libjvm.so`__1cJJavaCallsEcall6FpnJJavaValue_nMmethodHandle_ pnRJavaCallArguments_pnGThread __v_+0x28 libjvm.so`__1cRjni_invoke_static6FpnHJNIEnv__pnJJavaValue_ pnI_jobject_nLJNICallType_pnK_jmethodID_pnSJNI_ ArgumentPusher_pnGThread__v_+0x180 libjvm.so`jni_CallStaticVoidMethod+0x10f java`main+0x53d
Notice that the C and C++ stack frames from the Java virtual machine are presented symbolically using C++ “mangled” symbol names, and the Java stack frames are presented only as hexadecimal addresses. The following example shows a call to ustack with a non-zero string space:
# dtrace -n syscall::write:entry'/pid == $target/{ustack(50, 500); exit(0)}' -c "java -version" dtrace: description 'syscall::write:entry' matched 1 probe java version "1.5.0-beta3" Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0-beta3-b58) Java HotSpot(TM) Client VM (build 1.5.0-beta3-b58, mixed mode) dtrace: pid 5308 has exited CPU ID FUNCTION:NAME 0 35 write:entry libc.so.1`_write+0x15 libjvm.so`__1cDhpiFwrite6FipkvI_I_+0xa8 libjvm.so`JVM_Write+0x2f d0c5c946 libjava.so`Java_java_io_FileOutputStream_writeBytes+0x2c java/io/FileOutputStream.writeBytes java/io/FileOutputStream.write java/io/BufferedOutputStream.flushBuffer java/io/BufferedOutputStream.flush java/io/PrintStream.write sun/nio/cs/StreamEncoder$CharsetSE.writeBytes sun/nio/cs/StreamEncoder$CharsetSE.implFlushBuffer sun/nio/cs/StreamEncoder.flushBuffer java/io/OutputStreamWriter.flushBuffer java/io/PrintStream.write java/io/PrintStream.print java/io/PrintStream.println sun/misc/Version.print sun/misc/Version.print StubRoutines (1) libjvm.so`__1cJJavaCallsLcall_helper6FpnJJavaValue_ pnMmethodHandle_pnRJavaCallArguments_pnGThread __v_+0x187 libjvm.so`__1cCosUos_exception_wrapper6FpFpnJJavaValue_ pnMmethodHandle_pnRJavaCallArguments_pnGThread __v2468_v_+0x14 libjvm.so`__1cJJavaCallsEcall6FpnJJavaValue_nMmethodHandle _pnRJavaCallArguments_pnGThread__v_+0x28 libjvm.so`__1cRjni_invoke_static6FpnHJNIEnv__pnJJavaValue_pnI _jobject_nLJNICallType_pnK_jmethodID_pnSJNI _ArgumentPusher_pnGThread__v_+0x180 libjvm.so`jni_CallStaticVoidMethod+0x10f java`main+0x53d 8051b9a
The above example output demonstrates symbolic stack frame information for Java stack frames. There are still some hexadecimal frames in this output because some functions are static and do not have entries in the application symbol table. Translation is not possible for these frames.
The ustack symbol translation for non-Java frames occurs after the stack data is recorded. Therefore, the corresponding user process might exit before symbol translation can be performed, making stack frame translation impossible. If the user process exits before symbol translation is performed, dtrace will emit a warning message, followed by the hexadecimal stack frames, as shown in the following example:
dtrace: failed to grab process 100941: no such process c7b834d4 c7bca85d c7bca1a4 c7bd4374 c7bc2628 8047efc
Techniques for mitigating this problem are described in Chapter 12, User Process Tracing.
Finally, because the postmortem DTrace debugger commands cannot perform the frame translation, using ustack with a ring buffer policy always results in raw ustack data.
The following D program shows an example of ustack that leaves strsize unspecified:
syscall::brk:entry /execname == $$1/ { @[ustack(40)] = count(); }
To run this example for the Oracle Solaris prstat command use the following command:
# dtrace -s brk.d prstat dtrace: script 'brk.d' matched 1 probe ^C libc.so.1`_brk_unlocked+0xa libc.so.1`sbrk+0x2c libc.so.1`_morecore+0x112 libc.so.1`_malloc_unlocked+0x182 libc.so.1`realloc+0x39f prstat`Realloc+0x21 prstat`Zalloc+0x17 prstat`fd_init+0x2a prstat`main+0x55 prstat`0x4047dc 1 libc.so.1`_brk_unlocked+0xa libc.so.1`sbrk+0x2c libc.so.1`_morecore+0x112 libc.so.1`_malloc_unlocked+0x182 libc.so.1`malloc+0x31 libc.so.1`calloc+0x57 libcurses.so.1`setupterm+0xacc libcurses.so.1`newscreen+0x87 libcurses.so.1`initscr32+0x53 prstat`curses_on+0x1f prstat`main+0x7f0 prstat`0x4047dc 1 ...