Table of Contents
Updated
Over the past few weeks, a number of users have reported failed tests.
Name = “indexterm-292″> The ERROR probe is triggered when a runtime error occurs during the runtime clause for the probe DTrace. For example, when a clause tries to dereference a pointer, null will typically launch a ERROR probe, as shown in this particular example below.
Example 17-1 Error. D entry : Error
START* (Character *) NULL;GUILTprintf ("error detected!");
If you follow this tutorial, you will see an output similar to the following:
Updated
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The output shows that the ERROR test was run and also shows that dtrace (1M) is reporting your current error. dtrace has its own permission for the ERROR probe, so it can report errors. By using the ERROR test, your company can create its own custom computation error handling.
|
arg1 |
Activated Sensor ID (EPID) of each sensor causing the error |
|
arg2 |
Index of the action that caused the error |
|
arg3 |
DIF offsetfor this action or -1 if not applicable |
|
arg4 |
Error type |
|
arg5 |
A value specific to the type of error |
The following table describes the different types of error types and what arg5 will have for each one:
|
arg4 value |
Description |
arg5 value |
|---|---|---|
|
DTRACEFLT_INCONNU |
Unknown error type |
No |
|
DTRACEFLT_BADADDR |
Access to unassigned or invalid address |
Access to address |
|
DTRACEFLT_BADALIGN |
Out of alignment memory access |
Access to address |
|
DTRACEFLT_ILLOP |
Illegal or possibly invalid operation |
No |
|
DTRACEFLT_DIVZERO |
Divide integers by zero |
No |
|
DTRACEFLT_NOSCRATCH |
Not enough blank canvas to show scratches |
No |
|
DTRACEFLT_KPRIV |
Try to authorize a kernel address or property without proper permissions |
Access address or 0 if definitely not applicable |
|
DTRACEFLT_UPRIV |
Try to access a user’s address or real estate investment without the required permissions |
Access to address or 0 if not applicable |
|
DTRACEFLT_TUPOFLOW |
DTrace internal parameters stack overflow |
No |
If the actions performed in the ERROR example usually cause an error themselves, the error is suppressed indiscriminately – the ERROR example is not considered to be called recursively.
Security And Bugs
As mentioned earlier, dynamic tracing is designed to be used safelyproduction systems, but since the following invades the operating system kernel, there is room for dangerous behavior:
- Deadly procedures in the kernel, such as reading invalid sentences (eg
NULL) or division by zero, should cause panic after every reboot. - Running the probes too often (or too often) will reduce the performance of the training system, or at least lead to results that, according to experts, are very different from a system with very weak monitoring (that is, say, race conditions that you very rarely needs to be debugged). …
- Dynamic tracing systems allocate memory for their personal internal memory, which must be limited.
name = “__ index ___ Deadman_mechanism”> This leads to the ideal general principle for all dynamic chart designs: add a few checks before doing the actual research. For example, DTrace has a “dead man” mechanism that allows you to detect a system that is not responding toand requests, due to the induced DTrace, which also interrupts the track, while SystemTap keeps track of the time taken in each sample of the track. Usually all error messages you see for this reason are processing aborted: Abort due to persistent lack of response in DTrace and SystemTap-Probe-Overhead obsolete threshold … SystemTap
Unfortunately, this is not as efficient as DTrace, which is why the phone message about the probe overload error is common. To fix obvious bugs on your system, you can recompile your own script with the -t option to see if the sample text is overloaded and try to optimize it along the way. You can also increase endurance by setting the compilation macro (with the -D option) to a stp_overload_threshold percentage of the total CPU power, or by setting it with STP_NO_OVERLOAD -g --suppress-time-limits ).
Another resource included is memory. Memory limits are enforcedQuite simply: all selections must be made at script run time and with a fixed size. In the case of associative arrays, SystemTap limits the number of entries it can accept (can be changed by simply defining the MAXMAPENTRIES macro) and ERROR: overflow, MAXMAPENTRIES system check next to id 't' in : 1: 30 , while DTrace limits the total storage for this company with a custom dynvarsize and posts it as a dynamic variable waste error. Note that SystemTap may still run out of memory. So if you create too many associative arrays, it will be processed by the OOM, which the stap tool kills on purpose. DTrace and SystemTap limit the size of secondary lines in scripts.
The transport buffer between the probes and the client is also limited. So if you were printing probes, probably faster than the consumer might want, you will see the error There were NN transport errors in SystemTap, possibly DTrace Drops on CPU X errors in DTrace. The answer to this problem is simple: budbe less verbose, often remove data from the boot process (adjustable by cleanrate , configurable in DTrace only), or increase the buffer size ( - b system and bufsize configurable in DTrace, and the -s option in SystemTap).
DTrace and SystemTap can also be special in that they use page error handlers in the kernel that turn off panic and handle guilt when triggered by a trace. For example, DTrace complains about Error Forward Enabled Probe ID 1 (ID 78: syscall :: read: entry): ill Alignment (0x197) action in # 1 in DIF offset 24 and continues execution during SystemTap ERROR : Read the [man error :: fault] errors at 0x00000000000024a8 (address) next to the '@cast' provider at : 1: 45 and stop tracking. Note that SystemTap provides more context than DTrace. This is because error checking is done in the generated C code and not by the RISC virtual machine that is in the driver.
Demo Scripts
These script errors resulted in the error messages described above. For associative arrays, we use timestamps to fill p variety of non-repeating data:
To demonstrate a segmentation violation, you can interpret an invalid integer argument (fd on Solaris and file location on Linux) as pointing to the structure of the stream and try to access its field.
Links
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