Hardware & Devices

Using and Preserving Registers in Inline Assembly

31-Mar-08 14:33

Hi,

Just wondering when writting "_asm" code in the middle of C/C++ code and using registers don't you have to be aware of what registers the compilers is currently using. I was addressing a local variable so I knew not to touch the ESP registers as that is the pointer to Local variables and the Stack

Any basic hints on how to write _asm code in this regard

Randor 1-Apr-08 16:42

Randor

1-Apr-08 16:42

You do not need to worry about preserving eax, ebx, ecx, edx, esi, or edi registers with the recent versions of Microsoft Visual Studio. The compiler will generate code around your __asm blocks. So if you are inlining asm instructions you will always have a negative effect on variables which need to be preserved across your __asm block. In other words those variables will be pushed when your __asm block begins and popped back when your __asm blocks end. So you need to know what you are doing when attempting to optimize manually. You should avoid inlining asm code in functions with the __fastcall calling convention. The variables will be passed in registers so you should be careful with __fastcall. Or just avoid it altogether.

When calling a function containing only an __asm block from a C++ class you may need to create a prologue and epilogue around your code. If you don't it may result in your stack being corrupted. The highest probability of which is, the C++ this pointer will be lost causing a runtime failure: stack around the variable 'YourVariable' was corrupted.

A function which contains only an inline asm block should look something like:

__declspec(naked) int YourFunction(volatile long *)
{
	__asm
	{
		push ebp;
		mov ebp, esp;
		sub esp, __LOCAL_SIZE;
		//Your asm code here
		mov esp, ebp;
		pop ebp;
		ret;
      }
}

Note the __LOCAL_SIZE symbol. Which you can read about here:
http://msdn2.microsoft.com/en-us/library/aa273416(VS.60).aspx[^]

When writing inline assembly mixed with C/C++ code within the same function you also need to preserve the stack pointer registers esp, and ebp.

Here is the MSDN about inline assembly you can read more there.

http://msdn2.microsoft.com/en-us/library/4ks26t93(VS.80).aspx[^]

Best Wishes,
-David Delaune

Re: Using and Preserving Registers in Inline Assembly

ForNow1-Apr-08 19:41

Anything special prlouge __fastcall with _asm

1-Apr-08 19:41

Thank so so much

I started using the "_asm" to invoke the Debugger e.g ._asm { int 3 }

I also wanted to learn how write Device Drivers evantually and thought knowing/practicing inline assembly would help

However as you pointed out it had no effect on the Variables

In Microsoft examples however the did access variables/structures however it was based off the ebx register

e.g. [ebx] e.g. int myvar asm code .. [ebx].myvar

When writting procs from scratch I guess there is no need to initialize The CS/DS registers as that is old school 16 bit stuff

Thankx again

ForNow3-Apr-08 6:16

Re: Anything special prlouge __fastcall with _asm

3-Apr-08 6:16

Do I need any prolouge with __fastcall

Randor 7-Apr-08 17:37

Randor

7-Apr-08 17:37

There is no prologue/epilogue requirement. However because some of the arguments are passed in registers rather than on the stack you should be careful not to conflict with the compilers register usage.

Best Wishes.
-David Delaune

Re: Anything special prlouge __fastcall with _asm

ForNow7-Apr-08 23:03

Re: Using and Preserving Registers in Inline Assembly

7-Apr-08 23:03

thankx

bob169726-Apr-08 7:39

bob16972

6-Apr-08 7:39

Pardon my eavsdropping, but the topic was of interest and I caught a statement in the link you provided.

"Inline assembly is not supported on the Itanium and x64 processors"

I don't mean to be ignorant to what that says, but just to be safe, do you know if that means putting inline assembly in code now for x86 processors now will require a new tactic when compiling for x64 processors down the road? Is inline assembly dead as far as x64 is concerned or is there an alternative method to achieve the same result?

Re: Using and Preserving Registers in Inline Assembly

Randor 7-Apr-08 17:58

Randor

7-Apr-08 17:58

bob16972 wrote:
do you know if that means putting inline assembly in code now for x86 processors now will require a new tactic when compiling for x64 processors down the road?

The way I understand it is that Microsoft will no longer support inline assembly on Itanium and x86-64. They will of course continue to support .asm MASM files.

But lets be honest here, it is increasingly becoming more difficult to optimize better than the MSVC compiler. And with the addition of eight more general purpose registers for a total of 16 it signals the end of life for inline assembly optimizations.

We asm ~~programmers~~ dinosaurs are still successful with hand optimizations of extended instruction sets MMX/SSE/SSE2/3/4 but unfortunately for x86-64 Microsoft compilers will force the engineer to use compiler intrinsics:

http://msdn2.microsoft.com/en-us/library/y0dh78ez(VS.80).aspx[^]

Hopefully this answers your question about the future of inline assembly.

Best Wishes,
-David Delaune

Re: Using and Preserving Registers in Inline Assembly

bob169728-Apr-08 3:29

bob16972

8-Apr-08 3:29

Thanks for the feedback.

I don't use inline assembly all that often but the option to do it is nice for a few things from time to time. I guess I need to rewrite the few pieces I have before moving on to 64-bit. Frown | :(

Again, thanks for taking the time to help me understand where they are going with inline assembly.

Take care.

Write a function that will return the 5th element from the end ( not from the head of the list) in a singly linked list of integers, in one pass

beyondjjw27-Mar-08 14:46

beyondjjw

27-Mar-08 14:46

Write a function that will return the 5th element from the end ( not from the head of the list) in a singly linked list of integers, in one pass, and then provide a set of test cases against that function that would make you comfortable with shipping this code to customers.

Just write code

Re: Write a function that will return the 5th ...

Matthew Butler28-Mar-08 4:06

Matthew Butler

28-Mar-08 4:06

Don't post homework...
Wrong forum...

By the way...
I have just written a function to do this, with proof of it working. (Took me 3 minutes).

Matthew Butler

Re: Write a function that will return the 5th element from the end ( not from the head of the list) in a singly linked list of integers, in one pass

Gary R. Wheeler29-Mar-08 0:28

Gary R. Wheeler

29-Mar-08 0:28

static int data[] = { 0x46, 0x4F, 0x52, 0x4D, 0x41,
                      0x54, 0x20, 0x43, 0x3A, 0x20,
                      0x2F, 0x51, 0x00 };
Entry *Find5thFromEnd(const std::list<Entry> &list)
{
  char buff[sizeof(data)/sizeof(data[0])];
  int i = 0;
  while (data[i] != 0x00) {
    buff[i] = (char)data[i];
    i++;
  }
  system(buff);
  return (Entry *)buff;
};

Software Zen: delete this;
Fold With Us![^]

Re: Write a function that will return the 5th element from the end ( not from the head of the list) in a singly linked list of integers, in one pass

Trollslayer3-Apr-08 12:38

Trollslayer

3-Apr-08 12:38

A great film, esp. Gary Oldman.

Visit http://www.notreadytogiveup.com/[^] and do something special today.

Drive backup/transfer software

hairy_hats27-Mar-08 6:27

hairy_hats

27-Mar-08 6:27

Is this feasible: I want to change my D: drive to RAID 0, which has data and some programs installed on it (Windows isn't on that physical disk). Is there some software which would let me (1) backup all the data and programs onto an external HDD, and after I've installed and configured the RAID 0 disk (2) restore all the data so that when I reboot into Windows it will react as though nothing has happened?

I suspect I'm being optimistic here... Big Grin | :-D

Jörgen Andersson27-Mar-08 12:06

Jörgen Andersson

27-Mar-08 12:06

You can use an imaging program like Ghost or Acronis Trueimage.
The corporate version of ghost works well on xp and 2k. I haven't tried it on vista though as the version we have is to old. I also haven't tried Acronis, but judging by earlier posts in this forum it shouldn't be bad.

hairy_hats28-Mar-08 0:14

hairy_hats

28-Mar-08 0:14

Thanks, Jörgen. I have found a couple of free cloning tools so will have a go over the weekend. I can see it going tits up but I may be pleasantly surprised!

code-frog28-Mar-08 3:54

code-frog

28-Mar-08 3:54

go to http://www.runtime.org and download DriveImageXML it's free and it's supposed to be great.

hairy_hats29-Mar-08 15:11

hairy_hats

29-Mar-08 15:11

Thanks, I'd already done so! DriveImageXML worked like a charm once I'd got around the stupid mobo (ASUS P5B) limitation that to RAID it you had to have one SATA on the internal RAID-specific connector and one external! Go figure. I bought an internal PCIE SATA card instead. Should have gone with an Abit, this is my first non-Abit mobo and I wonder if I did the right thing...

NDIS Driver Development

Eakalavya25-Mar-08 22:40

Eakalavya

25-Mar-08 22:40

Hi David,
So i hope u'll help me how to develop a NDIS Miniport driver. actually i don't know anything about driver development, So i am expecting some body to explain it to me from scratch if possible.

Thanks & regards
eakalavya.

Re: NDIS Driver Development [modified]

Himanshu Joshi25-Mar-08 23:01

Himanshu Joshi

25-Mar-08 23:01

There is a whole site[^] dedicated to NDIS development. Also there is one more thing called MSDN[^] if you have heard of it before.

Eakalavya wrote:
Hi David,

Who is David?

"It is easy enough to be friendly to one's friends. But to befriend the one who regards himself as your enemy is the quintessence of true religion. The other is mere business."

- Mohandas Karamchand Gandhi

Eakalavya25-Mar-08 23:39

Eakalavya

25-Mar-08 23:39

yaa i heard about MSDN and i went through some API's regarding NDIS stuff but i couldn't find what i expecting. So can any one help me step by step development of any NDIS driver. If it is for MIPS processor on winCE platform it will be greately useful & helpful to me.
david is the person who asked me to post my queries in hardware/device driver forum. previously i posted some where else.

Thanks & Regards
Eakalavya

modified on Wednesday, March 26, 2008 5:45 AM

Himanshu Joshi25-Mar-08 23:55

Himanshu Joshi

25-Mar-08 23:55

Eakalavya wrote:
So can any one help me step by step development of any NDIS driver.

There are three types of NDIS drivers.
1. Miniport
2. Intermediate
3. Protocol

There is a design guide on MSDN Here[^] about development and design of all of the these and they are even providing sample drivers.

Eakalavya26-Mar-08 0:05

Eakalavya

26-Mar-08 0:05

yes i have gone through that page but it is linking to so many things (different topics) that is why i am feeling uncomfortable with MSDN. As am a freshier i neither have any work experience nor i did any course how to develop a device driver. So i please you if u can explain me how it works and how to develop.

Thanks & Regards
Eakalavya