Edit

.SAVEXMM128

Generates either a UWOP_SAVE_XMM128 or a UWOP_SAVE_XMM128_FAR unwind code entry for the specified XMM register and offset using the current prologue offset. Microsoft Assembler (MASM) chooses the most efficient encoding.

Syntax

.SAVEXMM128 xmmreg , offset

Remarks

Use .SAVEXMM128 with ml64.exe to specify how a frame function unwinds. You can only use it within the prologue, which extends from the PROC FRAME declaration to the .ENDPROLOG directive. These directives generate unwind metadata (.xdata and .pdata sections) but don't produce executable code. Precede .SAVEXMM128 by the instructions that actually implement the actions to be unwound. To ensure agreement, wrap both the unwind directives and the code they're meant to unwind in a macro.

offset must be a multiple of 16.

Unwind Version 3 behavior

Important

Unwind Version 3 support is experimental and is subject to change. Enable it by using ml64.exe /unwindv3.

In Unwind Version 3, .SAVEXMM128 emits either a WOD_SAVE_XMM128 or a WOD_SAVE_XMM128_FAR unwind code entry. Microsoft Assembler (MASM) selects the most efficient encoding based on the size of offset:

Unwind code Condition
WOD_SAVE_XMM128 offset can be encoded as a scaled 16-bit value
WOD_SAVE_XMM128_FAR offset requires a full 32-bit value

Note

In Unwind Version 1 the directives come after the instruction. In Unwind Version 3, the directives come before the instruction. .SAVEXMM128 must appear before the instruction it describes. This requirement is the opposite of Version 1, where the directive follows the instruction.

Example for unwindv3

; ml64 /unwindv3 ex1.asm /link /entry:Example1 /SUBSYSTEM:CONSOLE
_text SEGMENT
Example1 PROC FRAME
   .allocstack 030h
   sub rsp, 030h
   .savexmm128 xmm6, 0
   movdqa [rsp], xmm6
   .savexmm128 xmm7, 010h
   movdqa [rsp+010h], xmm7
.endprolog
   ; rest of function ...
   movdqa xmm7, [rsp+010h]
   movdqa xmm6, [rsp]
   add rsp, 030h
   ret
Example1 ENDP
_text ENDS
END

The epilogue counterpart is .RESTOREXMM128.

See also

x64 Unwind Version 3 (experimental)
Directives reference
MASM BNF Grammar
MASM for x64 (ml64.exe)

  • Last updated on