Saving xmm registers

[Gunther]

That question isn't relevant for every application, but there could be situations where a large amount of multimedia registers are in use. MS says in the x64 Software Conventions for VC that xmm0 - xmm3 are volatile; the other registers xmm4 - xmm15 must be preserved as needed by caller. http://msdn.microsoft.com/en-us/library/9z1stfyw.aspx

Has anyone a clue how to do that in a reasonable manner?

Gunther

[qWord]

Save them like GPRs on the (aligned) stack using MOVDQA.  jWasm can also do this with the USES statement:

Code Select Expand

foo PROC uses xmm5 xmm6 ...

[Gunther]

Thank you qWord for the fast reply. Do you have a small code example?

Gunther

[qWord]

hi,
not sure what example you expect, but maybe this helps:

Code Select Expand

option casemap :none
option frame:auto
option procalign:16
option fieldalign:8

JWASM_STORE_REGISTER_ARGUMENTS  EQU 1
JWASM_STACK_SPACE_RESERVATION   EQU 2

option win64:JWASM_STACK_SPACE_RESERVATION ; see documentation


.code
; hand crafted
foo1:
    sub rsp,8+2*16 + 4*8    ; 8 = align 16
                            ; 2*16 = XMM registers
                            ; 4*8 = shadow space - only needed, if APIs are called
   
    movdqa OWORD ptr [rsp+4*8+00],xmm5
    movdqa OWORD ptr [rsp+4*8+16],xmm6
   
    ; ...
   
    movdqa xmm5,OWORD ptr [rsp+4*8+00]
    movdqa xmm6,OWORD ptr [rsp+4*8+16]
   
    add rsp,8+2*16+4*8
    ret

foo2 proc FRAME uses xmm5 xmm6 myArg:DWORD
LOCAL x:REAL8   
   
    ;...
   
    ret
   
foo2 endp


main proc FRAME
   
    call foo1

    invoke foo2,123

    ret
   
main endp
end main

jwasm.exe  /win64 src.asm
polink /SUBSYSTEM:CONSOLE src.obj

Also take a look in the examples coming with jWasm.

[Gunther]

Hi qWord,

I've downloaded the jWasm package and I think your example will help. Thank you. You're one of the jWasm contributors?

Gunther

[qWord]

You're one of the jWasm contributors?

yes, bug reports for jWasm and WinInc  :P

[Gunther]

Hi qWord,

yes, bug reports for jWasm and WinInc  :P

I hope it's not much to do for tracking bugs. Jwasm is a well written tool and rock solid, so far as I know.

Gunther

[frktons]

That question isn't relevant for every application, but there could be situations where a large amount of multimedia registers are in use. MS says in the x64 Software Conventions for VC that xmm0 - xmm3 are volatile; the other registers xmm4 - xmm15 must be preserved as needed by caller. http://msdn.microsoft.com/en-us/library/9z1stfyw.aspx

Has anyone a clue how to do that in a reasonable manner?

Gunther

Another simple way I can figure, but slower than the stack, is to push them
to RAM variables declared for that use:

Code Select Expand



.data?

align 16
xmm0_var DB 16 DUP (?)
xmm1_var DB 16 DUP (?)

....

.code

movdqa oword ptr xmm0_var, xmm0 ; push the xmm0 register
movdqa xmm1, oword ptr xmm0_var ; pop it to another xmm register

or a little bit faster:

movaps oword ptr xmm0_var, xmm0          ; push the xmm0 register
pshufd  xmm1, oword ptr xmm0_var, 0E4H ; pop it to another xmm register



[Gunther]

Another simple way I can figure, but slower than the stack, is to push them
to RAM variables declared for that use:

Code Select Expand



.data?

align 16
xmm0_var DB 16 DUP (?)
xmm1_var DB 16 DUP (?)

....

.code

movdqa oword ptr xmm0_var, xmm0 ; push the xmm0 register
movdqa xmm1, oword ptr xmm0_var ; pop it to another xmm register

or a little bit faster:

movaps oword ptr xmm0_var, xmm0, 0E4H ; push the xmm0 register
pshufd  xmm1, oword ptr xmm0_var, 0E4H ; pop it to another xmm register



yes, of course. Thank you for the answer, Frank.

Gunther