I am trying to understand how to implement a Code Coverage tool using the Win32 Debugging API.
My thinking has been to utilize the Win32 Debugging API to launch a process in debug mode - and track what CPU instructions has been executed. After having tracked all CPU instructions I would then use the map file to map it to what source code lines were executed.
As far as I understand, there would be two ways of knowing what CPU instructions have been executing.
Would be to launch the process in debug mode - set all threads in single step mode and let the debugging app note all instructions that has been executed
Would be make a more intelligent approach where you would know a lot more about x86 instructions and basically replace the next branch instruction with a breakpoint. Then keeping track of the delta instructions between the two breakpoints.
Update - new suggested approaches inspired by Michael's response:
Start with the map file and insert breakpoints for the beginning of each line and let the debug framework be notified every time a breakpoint hits.
Start with the map file - binary instrumentation to insert a "hook" that get called at entry of each source line - avoiding the callback through the debugger framework.
Using a VM Technology - such as VMware to find out what instructions in a particular process was executed - I don't fully understand this approach...
Could someone validate one of the approaches above or maybe suggest an alternative - please note that the use case is line-by-line code coverage and not performance profiling - thus we need to know if each single source line is visited.
My primary goal (although no particular plan is in place...) would be to create a simple code coverage tool for Delphi primarily.
Thanks!
One approach is hooking all api calls and function calls to compare with table made from the source. Thus you discovers what is covered.
There is many api for hooking, one is Trappola API hooking
This could work - each single step event will create an exception and you could record the hit IP address in your map of executed code lines.
Unfortunately, I imagine this would be glacially slow. It'd be incredibly inefficient, as each single line of code results in 1000's of times more work, as an exception is generated, trapped, a message sent to your debugger, and then a round trip back after you record the hit. It might be better to try to set breakpoints instead for each covered line and clear them after they are hit. That'd be faster, but most likely still very slow.
The core problem is you're trying to use the debugger as a code coverage tool which it is not intended for. A quick search shows several code coverage tools for Delphi on the Internet.
I would suggest, in stead of hooking for each line of code, you can go for the each block. What I mean to say hook for block of codes. It will be faster and you can get the count of lines as well from the blocks count.
Related
I'm using the latest DWScript which has a TdwsDebugger component with it. However I'm not necessarily looking to provide debugging tools to the user - just visually show the current line number.
In the TdwsDebugger component, in its OnDebug event, expr.ScriptPos seems to provide me with this information. But I'm trying to figure out how to make use of this without actually "debugging".
How can I show current DWScript line number without implementing debugging?
When no debugger is active, there is no code actively maintaining any current "line" or other particular execution information, so that information is not available.
Basically, when not debugging, the script execution engine tries to avoid any debugging-related overhead, which includes maintaining current line number or sending debug events notifications.
I am using gocraft/web in a project and am trying to debug some high memory usage. gocraft/web uses reflection to call handlers. I've set up the net/http/pprof profiler which works very well, but the largest block of memory, and the one that I am iterested in, only shows reflect.Value.call as the function. That's not very helpful.
How can I get around the fact that gocraft/web is using reflection and dig deeper into the memory profile?
Here's an example of the profile output I am seeing:
Thanks to #thwd for filing http://golang.org/issue/11786 about this. This is a display issue in pprof. All the data is there, just being hidden. You can get the data you need by invoking pprof with the -runtime flag. It will also show data you don't need, but it should serve as a decent workaround until Go 1.6 is out.
The short answer is that you can't directly. reflect.Value.call calls reflect.call which forwards to runtime.reflectcall which is an assembly routine implemented in the runtime, for example for amd64, here. This circumvents what the profiler can see.
Your best bet is to invoke your handlers without reflection and test them like that individually.
Also, enabling the profiler to follow reflective calls would arguably be an acceptable change to propose for the next Go iteration. You should follow the change proposal process for this.
Edit: issue created.
I just played around a bit with Lua and tried the Koneki eclipse plugin, which is quite nice. Problem is that when I make changes in a function I'm debugging at the moment the changes do not become effective when saving the changes. So I'm forced to restart the application. Would be so nice if I could make changes in the debugger and they would become effective on the fly as for example with Smalltalk or to some extend as in hot code replacement in Java. Anybody has a clue whether this is possible?
It is possible to some degree with some limitations. I've been developing an IDE/debugger that provides this functionality. It gives you access to a remote console to execute commands in the context/environment of your running application. The IDE also supports live coding, which reloads modified code as you make changes to it; see demos here.
The main limitation is that you can't modify a currently running function (at least without changes to Lua VM). This means that the effect of your changes to the currently running function will only be seen after you exit and re-enter that function. It works well for environments that call the same function repeatedly (for example a game engine calling draw), but may not work in your case.
Another challenge is dealing with upvalues (values that are created outside of your function and are referenced inside it). There are methods to "read" current upvalues and re-create them when the (new) function is created, but it requires some code analysis to find what functions will be recreated to query them for upvalues, to get the current values, and then to create a new environment with those upvalue and assign proper values to them. My current implementation doesn't do this, which means you need to use global variables as a workaround.
There was also relevant discussion just the other day on the Lua mailing list.
I've been looking at lua and lvm.c. I'd very much like to implement an interface to allow me to control the VM interpreter state.
Cooperative multitasking from within lua would not work for me (user contributed code)
The debug hook gets me only about 50% of the way there, instruction execution limits, but it raises an exception which just crashes the running lua code - but I need to be able to tweak it even further.
I want to create a system where 10's of thousands of lua user scripts are running - individual threads would not work, and the execution limits would cause headache for beginning developers, I'm going to control execution speeds too. but ultimately
while true do
end
will execute forever, and I really don't care that it is.
Any ideas, help or other implementations that I could look at?
EDIT: This is not about sandboxing pretend I'm an expert in that field for this conversation
EDIT: I do not want to use an internally ran lua code coroutine based controller.
EDIT: I want to run one thread, and manage a large number of user contributed lua scripts, an external process level control mechansim would not scale at all.
You can search for Lua Sandbox implementations; for example, this wiki page and SO question provide some pointers. Note that most of the effort in sandboxing is focused on not allowing you to execute bad code, but not necessarily on preventing infinite loops. For better control you may need to combine Lua sandboxing with something like LXC or cpulimit. (not relevant based on the comments)
If you are looking for something Lua-based, lightweight, but not necessarily 100% foolproof, then you can try running your client code in a separate coroutine and set a debug hook on that coroutine that will be triggered every N-th line. In that hook you can check if the process you are running exceeded its quotes. You also need to take care of new coroutines started as those need to have their own hooks set (you either need to disable coroutine.create/wrap or to replace them with something that sets the debug hook you need).
The code in this case may look like:
local coro = coroutine.create(client_func)
debug.sethook(coro, debug_hook, "l", 1000) -- trigger hook on every 1000th line
It's not foolproof, because it may block on some IO operation and the debug hook will not help there.
[Edit based on updated question and comments]
Between "no lua code coroutine based controller" and "no external process control mechanism" I don't think you are left with much choice. It may be that your only option is to run one VM per user script and somehow give ticks to those VMs (there was a recent question on SO on this, but I can't find it). Before going this route, I would still try to do this with coroutines (which should scale to tens of thousands easily; Tir claims supporting 1M active users with coroutine-based architecture).
The mechanism would roughly look like this: you install the debug hook as I shown above and from that hook you yield back to your controller, which then decides what other coroutine (user script) to resume. I have this very mechanism working in the Lua debugger I've been developing (although it only does it for one client script). This doesn't protect you from IO calls that can block and for that you may still need to have a watchdog at the VM level to see if it's been blocked for longer than needed.
If you need to serialize and deserialize running code fragments that preserve upvalues and such, then Pluto is probably your only option.
Look at implementing lua_lock and lua_unlock.
http://www.lua.org/source/5.1/llimits.h.html#lua_lock
Take a look at lulu. It is lua VM written on lua. It's for Lua 5.1
For newer version you need to do some work. But it's then you really can make a schelduler.
Take a look at this,
https://github.com/amilamad/preemptive-task-scheduler-for-lua
I maintain this project. It,s a non blocking preemptive scheduler for running lua code. Suitable for long running game scripts.
This has happened to me on more than one occasion and has led to many lost hours chasing a ghost. As typical, when I am debugging some really difficult timing-related code I start adding tons of OutputDebugString() calls, so I can get a good picture of the sequence of related operations. The problem is, the Delphi 6 IDE seems to be able to only handle that situation for so long. I'll use a concrete example I just went through to avoid generalities (as much as possible).
I spent several days debugging my inter-thread semaphore locking code along with my DirectShow timestamp calculation code that was causing some deeply frustrating problems. After having eliminated every bug I could think of, I still was having a problem with Skype, which my application sends audio to.
After about 10 seconds the delay between my talking and hearing my voice come out of Skype on the second PC that I was using for testing, the far end of the call, started to grow. At around 20 - 30 seconds the delay started to grow exponentially and at that point triggered code I have that checks to see if a critical section was being held too long.
Fortunately it wasn't too late at night and having been through this before, I decided to stop relentlessly tracing and turned off the majority of the OutputDebugString(). Thankfully I had most of them wrapped in a conditional compiler define so it was easy to do. The instant I did this the problems went away, and it turned out my code was working fine.
So it looks like the Delphi 6 IDE starts to really bog down when the amount of OutputDebugstring() traffic is above some threshold. Perhaps it's just the task of adding strings to the Event Log debugger pane, which holds all the OutputDebugString() reports. I don't know, but I have seen similar problems in my applications when a TMemo or similar control starts to contain too many strings.
What have those of you out there done to prevent this? Is there a way of clearing the Event Log via some method call or at least a way of limiting its size? Also, what techniques do you use via conditional defines, IDE plug-ins, or whatever, to cope with this situation?
A similar problem happened to me before with Delphi 2007. Disable event viewing in the IDE and instead use DebugView from Sysinternals.
I hardly ever use OutputDebugString. I find it hard to analyze the output in the IDE and it takes extra effort to keep several sets of multiple runs.
I really prefer a good logging component suite (CodeSite, SmartInspect) and usually log to various files. Standard files for example are "General", "Debug" (standard debug info that I want to collect from a client installation as well), "Configuration", "Services", "Clients". These are all set up to "overflow" to a set of numbered files, which allows you to keep the logs of several runs by simply allowing more numbered files. Comparing log info from different runs becomes a whole lot easier that way.
In the situation you describe I would add debug statements that log to a separate logfile. For example "Trace". The code to make "Trace" available is between conditional defines. That makes turning it on pretty simple.
To avoid leaving in these extra debug statements, I tend to make the changes to turn on the "Trace" log without checking it out from source control. That way, the compiler of the build server will throw out "identifier not defined" errors on any statements unintentionally left in. If I want to keep these extra statements I either change them to go to the "Debug" log, or put them between conditional defines.
The first thing I would do is make certain that the problem is what you think it is. It has been a long time since I've used Delphi, so I'm not sure about the IDE limitations, but I'm a bit skeptical that the event log will start bogging down exponentially over time with the same number of debug strings being written in a period of 20-30 seconds. It seems more likely that the number of debug strings being written is increasing over time for some reason, which could indicate a bug in your application control flow that is just not as obvious with the logging disabled.
To be sure I would try writing a simple application that just runs in a loop writing out debug strings in chunks of 100 or so, and start recording the time it takes for each chunk, and see if the time starts to increase as significantly over a 20-30 second timespan.
If you do verify that this is the problem - or even if it's not - then I would recommend using some type of logging library instead. OutputDebugString really loses it's effectiveness when you use it for massive log dumps like that. Even if you do find a way to reset or limit the output window, you'd be losing all of that logging data.
IDE Fix Pack has an optimisation to improve performance of OutputDebugString
The IDE’s Debug Log View also got an optimization. The debugger now
updates the Log View only when the IDE is idle. This allows the IDE to
stay responsive when hundreds of OutputDebugString messages or other
debug messages are written to the Debug Log View.
Note that this only runs on Delphi 2007 and above.