Hi,

It seems that within inline assembly I can read a class variable but I can't set it. Is this a bug or is there a good reason for this?

uint myvar;

void main()
{
}

class AClass
{
uint myvar2;

this()
{
asm
{
mov EAX,myvar;
mov myvar,EAX;  // this is fine

mov EAX,myvar2; // no problem reading
mov myvar2,EAX;	// doesn't compile - bad type/size of operands 'mov'
}
}
}

pmoore schrieb am 2006-05-20:
> Hi,
>
> It seems that within inline assembly I can read a class variable but I can't set it. Is this a bug or is there a good reason for this?
>
> uint myvar;
>
> void main()
> {
> }
>
> class AClass
> {
> uint myvar2;
>
> this()
> {
> asm
> {
> mov EAX,myvar;
> mov myvar,EAX;  // this is fine
>
> mov EAX,myvar2; // no problem reading
> mov myvar2,EAX;	// doesn't compile - bad type/size of operands 'mov'
> }
> }
> }

mov EAX,myvar2; seems to move the offset of myvar2 - not the value:

# import std.stdio;
#
# class C{
#    int i;
#
#    void foo(){
#       int x;
#
#       asm{
#          mov EAX, i;
#          mov x, EAX;
#       }
#
#       writefln("%s at 0x%X -> 0x%X, %s", i, &i, x, x);
#       writefln("offset of i: %s", i.offsetof);
#    }
# }
#
# int main(){
#    C c = new C();
#    c.foo();
#
#    return 0;
# }

What you are looking for is:
#       void* p = this;
#
#       asm{
#          mov EBX, p;
#          mov EAX, [EBX+myvar2];
#          // something productive here
#          mov [EBX+myvar2], EBX;
#       }

Thomas

Thomas Kuehne schrieb am 2006-05-21:
>
> pmoore schrieb am 2006-05-20:
>> Hi,
>>
>> It seems that within inline assembly I can read a class variable but I can't set it. Is this a bug or is there a good reason for this?

> What you are looking for is:
> #       void* p = this;
> #
> #       asm{
> #          mov EBX, p;
> #          mov EAX, [EBX+myvar2];
> #          // something productive here
> #          mov [EBX+myvar2], EBX;
> #       }

The last line should have been:

mov [EBX+myvar2], EAX;

Thomas

Thomas,

You are right. Now that I think about it again it would be impossible for the compiler to know at runtime what the address of a class local variable would be so it makes sense to be an offset.

Thanks for taking the time to point this out.


In article <1qv6k3-m9f.ln1@birke.kuehne.cn>, Thomas Kuehne says...
>
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>Thomas Kuehne schrieb am 2006-05-21:
>>
>> pmoore schrieb am 2006-05-20:
>>> Hi,
>>>
>>> It seems that within inline assembly I can read a class variable but I can't set it. Is this a bug or is there a good reason for this?
>
>> What you are looking for is:
>> #       void* p = this;
>> #
>> #       asm{
>> #          mov EBX, p;
>> #          mov EAX, [EBX+myvar2];
>> #          // something productive here
>> #          mov [EBX+myvar2], EBX;
>> #       }
>
>The last line should have been:
>
>mov [EBX+myvar2], EAX;
>
>Thomas
>
>
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