.SAVEREG

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

Syntax

.SAVEREG reg, offset

Remarks

Use .SAVEREG 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 .SAVEREG with 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.

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, .SAVEREG emits either a WOD_SAVE_NONVOL or a WOD_SAVE_NONVOL_FAR unwind code entry. MASM selects the most efficient encoding based on the size of offset:

Unwind code	Condition
`WOD_SAVE_NONVOL`	offset can be encoded as a scaled 16-bit value
`WOD_SAVE_NONVOL_FAR`	offset requires a full 32-bit value

Note

In Unwind Version 1, the directive appears after the corresponding instruction. In Unwind Version 3, the directive appears before the instruction. .SAVEREG 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 020h
   sub rsp, 020h
   .savereg rbx, 0
   mov [rsp], rbx
   .savereg rsi, 8
   mov [rsp+8], rsi
.endprolog
   ; rest of function ...
   mov rsi, [rsp+8]
   mov rbx, [rsp]
   add rsp, 020h
   ret
Example1 ENDP
_text ENDS
END

The epilogue counterpart is .RESTOREREG.

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Last updated on 2026-05-12