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How to access a 'Static' variable with inline assembly?
http://forums.purebasic.com/english/viewtopic.php?f=35&t=70689		 Page 1 of 1
Author:  Mijikai [ Fri May 11, 2018 8:40 am ]
Post subject:  How to access a 'Static' variable with inline assembly?
How can i change the content of 'Address' with inline assembly?

Code:
Code:
;PB x64 v.5.62

Procedure.i TestFnc()
  Static Address.i
  !mov qword[p.v_Address],123;<- does not work for 'Static' !
  Debug Address
EndProcedure

TestFnc()
Author:  Fred [ Fri May 11, 2018 8:46 am ]
Post subject:  Re: How to access a 'Static' variable with inline assembly?
If you want to look that, the best is to generate the assembly code with the commandline compiler (--commented switch) and look how it is named. You will save a lot of time when using inline ASM.
Author:  Mijikai [ Fri May 11, 2018 9:19 am ]
Post subject:  Re: How to access a 'Static' variable with inline assembly?
Fred wrote:
If you want to look that, the best is to generate the assembly code with the commandline compiler (--commented switch) and look how it is named. You will save a lot of time when using inline ASM.


Thanks :)

Heres how it works:
Code:
;-> so_PROCEDURENAME.v_VARIABLE


I found something im curious about:

If we have a Procedure that does not return a value PB does this:
Code:
...
xor rax,rax
add rsp,28
ret


However if we return a value it looks like this:
Code:
...
jmp @f
xor rax,rax
@@:
add rsp,28
ret


why is the jmp & xor even in there ?
Author:  wilbert [ Fri May 11, 2018 9:28 am ]
Post subject:  Re: How to access a 'Static' variable with inline assembly?
Mijikai wrote:
How can i change the content of 'Address' with inline assembly?

You could do it like this
Code:
;PB x64 v.5.62

Procedure.i TestFnc()
  Static Address.i
  Protected *Address = @Address
  !mov rdx, [p.p_Address]
  !mov qword [rdx],123
  Debug Address
EndProcedure

TestFnc()

It does produce a bit of additional code and therefore is slightly slower but it does have the advantage that the reference to *Address (local variable) stays the same.
The reference to a static value changes when the procedure is included in a module.
Author:  Mijikai [ Fri May 11, 2018 10:34 am ]
Post subject:  Re: How to access a 'Static' variable with inline assembly?
wilbert wrote:
...
Code:
;PB x64 v.5.62
Procedure.i TestFnc()
  Static Address.i
  Protected *Address = @Address
  !mov rdx, [p.p_Address]
  !mov qword [rdx],123
  Debug Address
EndProcedure

TestFnc()

It does produce a bit of additional code and therefore is slightly slower but it does have the advantage that the reference to *Address (local variable) stays the same.
The reference to a static value changes when the procedure is included in a module.


Thanks, i didnt think of that way :)
Author:  CELTIC88 [ Fri May 11, 2018 2:46 pm ]
Post subject:  Re: How to access a 'Static' variable with inline assembly?
Mijikai wrote:
...
I found something im curious about:

If we have a Procedure that does not return a value PB does this:
Code:
...
xor rax,rax
add rsp,28
ret


However if we return a value it looks like this:
Code:
...
jmp @f
xor rax,rax
@@:
add rsp,28
ret


why is the jmp & xor even in there ?



so that "PB" can be adapted to any scenario
"is complex process!"
but you can optimize that.
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