function call parameters and ARM assembly

Hi,

I'm new to WinCE (and ARM assembler) and have been debugging my application.
When I look at my code disassembled, I noticed that in C++ a function call
will have parameters number 4 and above pushed onto the stack while
parameters 1-3 are put in r1-r3. As far as I can tell, I'm not compiling
optimized. Are there compile flags that I can use that force every parameter
to the stack prior to the function call? I know that it isn't optimal, but
some of our code depends on this behavior since we have an intermingling of
.asm and .cpp.

Any help appreciated. Thanks!

Steve
Mon Apr 25 20:33:38 CDT 2005

That's the defined and specified calling convention for the ARM compiler.
You can count on it and write your ASM code accordingly.

--
Steve Maillet
EmbeddedFusion
www.EmbeddedFusion.com
smaillet at EmbeddedFusion dot com

Woojung_DOT_Huh_AT_smsc_DOT_com>
Mon Apr 25 21:44:10 CDT 2005

I don't think it is possible to force to generate code not to use r0~r3 as
1st~3rd function parms.
I guess you have to write own rouines in ASM to pass parms using stack to
call your sources.

"joevolleyball" wrote:

> Hi,
>
> I'm new to WinCE (and ARM assembler) and have been debugging my application.
> When I look at my code disassembled, I noticed that in C++ a function call
> will have parameters number 4 and above pushed onto the stack while
> parameters 1-3 are put in r1-r3. As far as I can tell, I'm not compiling
> optimized. Are there compile flags that I can use that force every parameter
> to the stack prior to the function call? I know that it isn't optimal, but
> some of our code depends on this behavior since we have an intermingling of
> .asm and .cpp.
>
> Any help appreciated. Thanks!

hel
Mon Apr 25 22:59:56 CDT 2005

You could double-up the first three args:

yourcall(a1,a2,a3,a1,a2,a3,a4,a5);

Wasted days and wasted nights and a little bit
of wasted bytes. But no harm, and no foul.
--
40th Floor - Software @ http://40th.com/
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parametric eq, xfeed, reverb: all on a ppc

joevolleyball
Tue Apr 26 15:56:44 CDT 2005

the problem I'll have with most of these replies is that my code is cross
platform and established in x86 land. So huge re-writes isn't ideal. I know
that x86 will behave similarly and pass the first two or 3 parameters in
registers when optimised, but when I compile with optimization off, then it
puts all of the parameters onto the stack prior to the function call. I was
hoping for similar behavior from the ARM compiler.

I guess I'll just have to hack around it.

thanks for all of your suggestions.

"joevolleyball" wrote:

> Hi,
>
> I'm new to WinCE (and ARM assembler) and have been debugging my application.
> When I look at my code disassembled, I noticed that in C++ a function call
> will have parameters number 4 and above pushed onto the stack while
> parameters 1-3 are put in r1-r3. As far as I can tell, I'm not compiling
> optimized. Are there compile flags that I can use that force every parameter
> to the stack prior to the function call? I know that it isn't optimal, but
> some of our code depends on this behavior since we have an intermingling of
> .asm and .cpp.
>
> Any help appreciated. Thanks!

joevolleyball
Tue Apr 26 16:01:06 CDT 2005

I'm confused...the parameters being passed in registers is the defined and
specified calling convention? Or the behavior that I desire and am not
seeing (all parameters pushed on the stack prior to a function call) is the
defined and specified calling convention?

"Steve Maillet (eMVP)" wrote:

> That's the defined and specified calling convention for the ARM compiler.
> You can count on it and write your ASM code accordingly.
>
> --
> Steve Maillet
> EmbeddedFusion
> www.EmbeddedFusion.com
> smaillet at EmbeddedFusion dot com
>
>
>

Steve
Wed Apr 27 00:10:45 CDT 2005

What you see is the defined behavior. There's no need for re-writes as your
assembly code is NOT platform independent just write the ARM code to use the
convention expected and used by the compiler. For more information See:
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/wcepbguide5/html/wce50oriarmcallingsequencespecification.asp

--
Steve Maillet
EmbeddedFusion
www.EmbeddedFusion.com
smaillet at EmbeddedFusion dot com