The data recording actions comprise the core DTrace actions. Each of these actions records data to the principal buffer by default, but each action may also be used to record data to speculative buffers. See Chapter 11, Buffers and Buffering for more details on the principal buffer. See Chapter 13, Speculative Tracing for more details on speculative buffers. The descriptions in this section refer only to the directed buffer, indicating that data is recorded either to the principal buffer or to a speculative buffer if the action follows a speculate
.
void trace(expression)
The most basic action is the trace
action, which takes a D expression as its argument and traces the result to the directed buffer. The following statements are examples of trace
actions:
trace(execname);
trace(curlwpsinfo->pr_pri);
trace(timestamp / 1000);
trace(`lbolt);
trace("somehow managed to get here");
void tracemem(address, size_tnbytes)
The tracemem
action takes a D expression as its first argument, address, and a constant as its second argument, nbytes. tracemem
copies the memory from the address specified by addr into the directed buffer for the length specified by nbytes.
void printf(string format, ...)
Like trace
, the printf
action traces D expressions. However, printf
allows for elaborate
printf
(
3C
)
-style formatting. Like
printf
(
3C
)
, the parameters consists of a format string followed by a variable number of arguments. By default, the arguments are traced to the directed buffer. The arguments are later formatted for output by
dtrace
(
1M
)
according to the specified format string. For example, the first two examples of trace
from
trace
could be combined in a single printf
:
printf("execname is %s; priority is %d", execname, curlwpsinfo->pr_pri);
For more information on printf
, see Chapter 12, Output Formatting.
void printa(aggregation) void printa(stringformat,aggregation)
The printa
action enables you to display and format aggregations. See Chapter 9, Aggregations for more detail on aggregations. If a format is not provided, printa
only traces a directive to the DTrace consumer that the specified aggregation should be processed and displayed using the default format. If a format is provided, the aggregation will be formatted as specified. See Chapter 12, Output Formatting for a more detailed description of the printa
format string.
printa
only traces a directive that the aggregation should be processed by the DTrace consumer. It does not process the aggregation in the kernel. Therefore, the time between the tracing of the printa
directive and the actual processing of the directive depends on the factors that affect buffer processing. These factors include the aggregation rate, the buffering policy and, if the buffering policy is switching, the rate at which buffers are switched. See Chapter 9, Aggregations and Chapter 11, Buffers and Buffering for detailed descriptions of these factors.
void stack(int nframes)
void stack(void)
The stack
action records a kernel stack trace to the directed buffer. The kernel stack will be nframes in depth. If nframes is not provided, the number of stack frames recorded is the number specified by the stackframes option. For example:
# dtrace -n uiomove:entry'{stack()}'
CPU ID FUNCTION:NAME
0 9153 uiomove:entry
genunix`fop_write+0x1b
namefs`nm_write+0x1d
genunix`fop_write+0x1b
genunix`write+0x1f7
0 9153 uiomove:entry
genunix`fop_read+0x1b
genunix`read+0x1d4
0 9153 uiomove:entry
genunix`strread+0x394
specfs`spec_read+0x65
genunix`fop_read+0x1b
genunix`read+0x1d4
...
The stack
action is a little different from other actions in that it may also be used as the key to an aggregation:
# dtrace -n kmem_alloc:entry'{@[stack()] = count()}'dtrace: description 'kmem_alloc:entry' matched 1 probe^Crpcmod`endpnt_get+0x47c rpcmod`clnt_clts_kcallit_addr+0x26f rpcmod`clnt_clts_kcallit+0x22 nfs`rfscall+0x350 nfs`rfs2call+0x60 nfs`nfs_getattr_otw+0x9e nfs`nfsgetattr+0x26 nfs`nfs_getattr+0xb8 genunix`fop_getattr+0x18 genunix`cstat64+0x30 genunix`cstatat64+0x4a genunix`lstat64+0x1c 1 genunix`vfs_rlock_wait+0xc genunix`lookuppnvp+0x19d genunix`lookuppnat+0xe7 genunix`lookupnameat+0x87 genunix`lookupname+0x19 genunix`chdir+0x18 1 rpcmod`endpnt_get+0x6b1 rpcmod`clnt_clts_kcallit_addr+0x26f rpcmod`clnt_clts_kcallit+0x22 nfs`rfscall+0x350 nfs`rfs2call+0x60 nfs`nfs_getattr_otw+0x9e nfs`nfsgetattr+0x26 nfs`nfs_getattr+0xb8 genunix`fop_getattr+0x18 genunix`cstat64+0x30 genunix`cstatat64+0x4a genunix`lstat64+0x1c 1 ...
void ustack(intnframes, intstrsize) void ustack(intnframes) 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 33, 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 Netscape web browser, .netscape.bin in default Solaris installations, use the following command:
# dtrace -s brk.d .netscape.bindtrace: description 'syscall::brk:entry' matched 1 probe^Clibc.so.1`_brk_unlocked+0xc 88143f6 88146cd .netscape.bin`unlocked_malloc+0x3e .netscape.bin`unlocked_calloc+0x22 .netscape.bin`calloc+0x26 .netscape.bin`_IMGCB_NewPixmap+0x149 .netscape.bin`il_size+0x2f7 .netscape.bin`il_jpeg_write+0xde 8440c19 .netscape.bin`il_first_write+0x16b 8394670 83928e5 .netscape.bin`NET_ProcessHTTP+0xa6 .netscape.bin`NET_ProcessNet+0x49a 827b323 libXt.so.4`XtAppProcessEvent+0x38f .netscape.bin`fe_EventLoop+0x190 .netscape.bin`main+0x1875 1 libc.so.1`_brk_unlocked+0xc libc.so.1`sbrk+0x29 88143df 88146cd .netscape.bin`unlocked_malloc+0x3e .netscape.bin`unlocked_calloc+0x22 .netscape.bin`calloc+0x26 .netscape.bin`_IMGCB_NewPixmap+0x149 .netscape.bin`il_size+0x2f7 .netscape.bin`il_jpeg_write+0xde 8440c19 .netscape.bin`il_first_write+0x16b 8394670 83928e5 .netscape.bin`NET_ProcessHTTP+0xa6 .netscape.bin`NET_ProcessNet+0x49a 827b323 libXt.so.4`XtAppProcessEvent+0x38f .netscape.bin`fe_EventLoop+0x190 .netscape.bin`main+0x1875 1 ...
void jstack(intnframes, intstrsize) void jstack(intnframes) void jstack(void)
jstack
is an alias for ustack
that uses the jstackframes option for the number of stack frames the value specified by , and for the string space size the value specified by the jstackstrsize option. By default, jstacksize defaults to a non-zero value. As a result, use of jstack
will result in a stack with in situ Java frame translation.