Re: Label adresses in inline assembly - C / C++ / MFC Discussion Boards

Remco Hoogenboezem5-Sep-09 11:21

5-Sep-09 11:21

Hello,

I would like to emit the lable addresses from a bit of inline assembly code into a branch table but I could not figure out how to do it.
I would say it should look something like this. At least the compiler emits something like this for a switch statement. I am using visual studio 2005.

__asm
{

mov eax,BRANCHTABLE
mov ecx,"Number between 0 and N"
jmp [eax+ecx*4]

BRANCHTABLE

&LABLE0
&LABLE1
&LABLE2
...
&LABLEN

LABLE0:
...
LABLE1:
...
LABLE2:
...
...
LABLEN
}

Thanks Wink | ;)

Re: Label adresses in inline assembly

Stuart Dootson5-Sep-09 13:46

Stuart Dootson

5-Sep-09 13:46

In MASM, possibly - but in inline assembly, you can't use operators such as & and you can't declare initialised data (which is what you're doing). I really don't know how you'd go about that. Maybe replace hte branchtable by a switch statement with interspersed inline assembly?

Java, Basic, who cares - it's all a bunch of tree-hugging hippy cr*p

Re: Label adresses in inline assembly

Randor 5-Sep-09 16:24

Randor

5-Sep-09 16:24

Hi Remco,

I created this little inline assembly sample for you. It loads the addresses of code labels into a jump table and allows you to jump to the offset based on a user choice. I commented each line.

#include "stdafx.h"

int _tmain(int argc, _TCHAR* argv[])
{
	#pragma pack (1)
		unsigned long table[3] = {0};
	#pragma pack(pop)

	char szError[] = "Invalid choice.\n";
	char szPrompt[] = "Enter a number between 1 and 3:\n";
	char szNotify[] = "You entered jump number: %d";
	char szFmt[] = "%d";
	int iChoice =0;
	int iSizeArray = (sizeof(table) / sizeof(table[0]));

	__asm
	{
		lea esi, table			;Load address of table into esi
		mov edx, DWORD PTR jump1		;Move address of jump1 into edx
		mov [esi], edx			;Move edx into table[0]
		add esi, 4				;Increment esi by size of unsigned long
		mov edx, DWORD PTR jump2		;Move address of jump2 into edx
		mov [esi], edx			;Move edx into table[1]
		add esi, 4				;Increment esi by size of unsigned long
		mov edx, DWORD PTR jump3		;Move address of jump3 into edx
		mov [esi], edx			;Move edx into table[2]
		lea eax, szPrompt			;Load effective address of prompt
		push eax				;push eax onto stack
#ifdef _DLL						;Are we dynamically linked to C runtime?
		call DWORD PTR printf		;Call dynamic linked printf
#else
		call printf				;Call static linked printf
#endif
		add esp, 4				;adjust stack pointer because we pushed eax
		lea eax, iChoice			;Load effective address of iChoice
		push eax				;Push it onto the stack
		lea ebx, szFmt			;Load effective address of fmt
		push ebx				;Push it on the stack
#ifdef _DLL						;Are we dynamically linked to C runtime?
		call DWORD PTR scanf		;Call dynamic linked scanf
#else
		call scanf				;Call static linked scanf
#endif
		add esp, 8				;adjust stack pointer because we pushed eax and ebx
		mov eax, iChoice			;Move iChoice value into eax
		mov ebx, iSizeArray		;Move the size of our array into ebx 
		cmp eax, ebx				;compare
		ja error				;Jump to the error lable if iChoice is larger than table array
		dec eax					;Decrement iChoice by 1 because the table is zero based array
		lea esi, table			;Load address of table into esi
		mov eax,[esi + 4*eax]		;Move value of table array onto eax by calculating offset
		jmp eax				;Jump to address stored in eax
jump1:
		mov eax, 1				;Move number 1 into eax
		jmp notify				;Absolute jump to notify label
jump2:
		mov eax, 2				;Move number 1 into eax
		jmp notify				;Absolute jump to notify label
jump3:
		mov eax, 3				;Move number 1 into eax
		jmp notify				;Absolute jump to notify label
error:
		lea eax, szError			;Load effective address of error
		push eax				;push eax onto stack
#ifdef _DLL						;Are we dynamically linked to C runtime?
		call DWORD PTR printf		;Call dynamic linked printf
#else
		call printf				;Call static linked printf
#endif
		add esp, 4				;adjust stack pointer because we pushed eax
		jmp end				;Absolute jump to end label
notify:
		push eax
		lea ebx, szNotify			;Load effective address of notify
		push ebx
#ifdef _DLL						;Are we dynamically linked to C runtime?
		call DWORD PTR printf		;Call dynamic linked printf
#else
		call scanf				;Call static linked printf
#endif
		add esp, 8				;adjust stack pointer because we pushed eax and ebx
end:
	}
	return 0;
}

Best Wishes,
-David Delaune

Re: Label adresses in inline assembly

Stuart Dootson5-Sep-09 23:39

Stuart Dootson

5-Sep-09 23:39

Oooh - nice. I'd wondered if there was a way to create the jump table as a C variable, but hadn't thought of initialising it in assembly code.

Java, Basic, who cares - it's all a bunch of tree-hugging hippy cr*p

Re: Label adresses in inline assembly

Remco Hoogenboezem6-Sep-09 0:56

Remco Hoogenboezem

6-Sep-09 0:56

Hello Stuart and David,

Thank you for your replies. Both solutions given are practical I think. I intended to use the branch table inside a time ciritcal part of my ray-tracer (ray vs axis aligned bounding box intersection test). I am building a stream ray-tracer using the sse ALU processing four rays in parallel. But the number of rays to process is not always a multiple of four to process the last 1,2 or 3 rays I thought to use a branch table. But I think I will make a funciton one for each case and use a switch statement ouside of the filter functions making the code easier to read and the c++ compiler does emit the code I would like.

Thank you for your help!!

Re: Label adresses in inline assembly

Luc Pattyn6-Sep-09 1:16

Luc Pattyn

6-Sep-09 1:16

A lot of jumps, and certainly those through a jump table, introduce a hickup in the instruction flow, as they are not predictable at all; so I'd rather avoid them.

assuming lots of rays I would take a different approach: if not a multiple of four, calculate one of the rays multiple times, e.g. duplicate the last ray one to three times so the number always is a multiple of 4. That probably will be simpler and may be faster.

Smile | :)

Luc Pattyn

Badger | [badger,badger,badger,badger...]

Have a look at my entry for the lean-and-mean competition; please provide comments, feedback, discussion, and don’t forget to vote for it! Thank you.

Re: Label adresses in inline assembly

Remco Hoogenboezem6-Sep-09 9:02

Remco Hoogenboezem

6-Sep-09 9:02

Yes conditional branches can be expensive causing pipeline stalls. But in my implementation using streams of rays there is only one hard to predict branch and that branch is only taken once per processed stream so it is not really that important. But a c++/assembly mix looks alittle bit messy. Thats why I removed the branch table from my inline assembly function to improve code readability at the expense of code size. Expanding the number of rays per stream to a multiple of four is for me not an option because rays are partitioned in place. Meaning that the filtered stream or output stream should be of the same length compared to the input stream.

Thanks Smile | :)

Re: Label adresses in inline assembly

Luc Pattyn6-Sep-09 9:32

Luc Pattyn

6-Sep-09 9:32

I forgot to mention one technique I often use in cases like this, where the expensive jump is taken only once (upon entry); I'll describe it in pseudo-code, it basically is a loop unroll by 4:

switch(count%4) {
case 0:
   // do step
   goto case1;
case 1:
   // do step
   goto case2;
case 2:
   // do step
   goto case3;
case 3:
   // do step
   count-=4;
   if (count>0) goto case0;
}

You can do this in any language, with a switch or with labels and jumps (and if the language allows fall-through, you may skip most of the goto's). In assembly, you would still need labels.

Smile | :)

Luc Pattyn

Have a look at my entry for the lean-and-mean competition; please provide comments, feedback, discussion, and don’t forget to vote for it! Thank you.

How to handle breaks during debugging

prithaa5-Sep-09 8:43

prithaa

5-Sep-09 8:43

Hello,

I placed a break in the function OnKeyDown() of a class derived from CRichEditCtrl. But when I press F5 and debug the code the code doesnt proceed further but when I remove the break in the fucntion the code goes ahead . Ith this I am not able debug the OnKeyDown.

What should be done ?

Pritha

Re: How to handle breaks during debugging

Stuart Dootson5-Sep-09 10:23

Stuart Dootson

5-Sep-09 10:23

prithaa wrote:
But when I press F5 and debug the code the code doesnt proceed further

Any further than what?

A breakpoint is meant to stop the code - you then have the option of what to do to make the execution progress.

Java, Basic, who cares - it's all a bunch of tree-hugging hippy cr*p

Re: How to handle breaks during debugging

prithaa5-Sep-09 20:19

prithaa

5-Sep-09 20:19

Thanks for your reply

But when I press F5 the code goes further that is the cursor moves ahead but the the action doesnt reflect in the execution like suppose after pressing a right arrow key I want the cursor to move further on the dialog then the cursor doesnt move on the dialog. whereas if I remove the break in the OnkeyDown then cursor moves in the dialog.

I hope the question is clear.

Pritha

Re: How to handle breaks during debugging

Stuart Dootson5-Sep-09 23:36

Stuart Dootson

5-Sep-09 23:36

Well, if I've understood you correctly, that's because the breakpoint keeps on breaking - every time you hit OnKeyDown

Java, Basic, who cares - it's all a bunch of tree-hugging hippy cr*p

Re: How to handle breaks during debugging

prithaa6-Sep-09 0:20

prithaa

6-Sep-09 0:20

Hello,

Thanks

What is the meaning of the breakpoint keeps breaking ?

Pritha

Re: How to handle breaks during debugging

Stuart Dootson6-Sep-09 0:57

Stuart Dootson

6-Sep-09 0:57

Every time you reach the OnKeyDown handler, it'll break at the breakpoint.

Java, Basic, who cares - it's all a bunch of tree-hugging hippy cr*p

Re: How to handle breaks during debugging

prithaa6-Sep-09 1:00

prithaa

6-Sep-09 1:00

Thanks

so I should not be using breaks in OnKeyDown() is it? .It is wrong to use it like that ?

Pritha

Re: How to handle breaks during debugging

Stuart Dootson6-Sep-09 1:03

Stuart Dootson

6-Sep-09 1:03

Well - what's the bug you're trying to find?

Java, Basic, who cares - it's all a bunch of tree-hugging hippy cr*p

Re: How to handle breaks during debugging

iraclyKv6-Sep-09 23:50

iraclyKv

6-Sep-09 23:50

Like all console input (keyboard, mouse events, windows focus and caret management) it's better to debug with writing debug messages to some (console or file). We either practice use Beep's.

Re: How to handle breaks during debugging

Iain Clarke, Warrior Programmer6-Sep-09 9:25

Iain Clarke, Warrior Programmer

6-Sep-09 9:25

OK... I see two scenarios you are describing:

1/ With breakpoint.
a) App is running.
b) Focus is in a window.
c) You press f5.
d) This is a key going down, so the CSomeControl::OnKeyDown handler is called.
e) You have a breakpoint there, so it, erm, breaks and goes into the debugger, allowing you to debug you OnKeyDown handler.

This is a good thing.

2/ With no breakpoint.
a) App is running.
b) Focus is in a window.
c) You press f5.
d) This is a key going down, so the CSomeControl::OnKeyDown handler is called.
e) You have no breakpoint there, so the application carries on happily.

This is a good thing.

This may be a language problem (don't apologise for that!), but I can maybe see a 3rd scenario:
1/ With breakpoint.
a) App is running.
b) Focus is in a window.
c) You press some key.
d) This is a key going down, so the CSomeControl::OnKeyDown handler is called.
e) You have a breakpoint there, so it, erm, breaks and goes into the debugger, allowing you to debug you OnKeyDown handler.
f) You press f5 to carry on with the program, and it no longer works

If #3 is true, then I bet you're forgetting to hold down the original key before continuing execution. You application may be thinking "so, when is he releasing that key!? It's been down for a long time...".

Iain.

I have now moved to Sweden for love (awwww).
If you're in Scandinavia and want an MVP on the payroll (or happy with a remote worker), or need cotract work done, give me a job! http://cv.imcsoft.co.uk/[^]

Re: How to handle breaks during debugging

prithaa6-Sep-09 19:11

prithaa

6-Sep-09 19:11

Thank you

I think the scenario is very much possible but then debugging OnKeyDown is pretty much difficult or not possible.

Thanks

Calling Unmanaged Class From DLL

İsmail Durmaz5-Sep-09 5:27

İsmail Durmaz

5-Sep-09 5:27

I want to call any class from unmanaged dll. How can i do?

// c++ side

class __declspec(dllexport) foo{
public:
    foo();
    ~foo();
    void sum(int a, int b);
};



// c# side
[...].class Foo{

    [...]
    void sum(int a, int b);
}

Re: Calling Unmanaged Class From DLL

«_Superman_»5-Sep-09 5:34

«_Superman_»

5-Sep-09 5:34

DllImport is the needed keyword here.
Take a look at Calling a DLL Export Directly from C#[^]

«_Superman_»
I love work. It gives me something to do between weekends.

Re: Calling Unmanaged Class From DLL

İsmail Durmaz5-Sep-09 5:37

İsmail Durmaz

5-Sep-09 5:37

but i want to call functions from class. dllimport calls only c style functions, it doesn't support c++ classes

Re: Calling Unmanaged Class From DLL

«_Superman_»5-Sep-09 5:42

«_Superman_»

5-Sep-09 5:42

I don't think you can do that.
You will need to convert the class into a COM component and then do a COM interop.

COM interop is what Microsoft recommends.

«_Superman_»
I love work. It gives me something to do between weekends.

Re: Calling Unmanaged Class From DLL

İsmail Durmaz5-Sep-09 5:43

İsmail Durmaz

5-Sep-09 5:43

thanks a lot

Re: Calling Unmanaged Class From DLL

Joe Woodbury5-Sep-09 8:39

Joe Woodbury

5-Sep-09 8:39

Not true. You can export/import a class.

articles here: DLLs are simple: Part 2[^] and here http://msdn.microsoft.com/en-us/library/a90k134d.aspx[^].

On top of that you can demonstrate this by creating a DLL with the Visual Studio wizard. Create a Win32 project and select export symbols.

I missed the C# part of your question. You are posting in the wrong forum. You also phrased your question incorrectly, which mislead me. You used the terms "unmanaged class" and "DLL" and then threw in "the C# side."

Incidentally, if you "own" the C++ side, you can add the CLR switch to its project and use C++/CLI. (Frankly, I usually find it easier to convert the class in question to C#, but I have done what I just described.)

Use Ctrl+Left/Right to switch messages, Ctrl+Up/Down to switch threads, Ctrl+Shift+Left/Right to switch pages.