Raw Pseudo Operations
The new home for Visual Studio documentation is Visual Studio 2017 Documentation on docs.microsoft.com.
The latest version of this topic can be found at Raw Pseudo Operations.
This topic lists the pseudo operations.
Remarks
| Pseudo operation | Description |
|---|---|
| PROC FRAME [:ehandler] | Causes MASM to generate a function table entry in .pdata and unwind information in .xdata for a function's structured exception handling unwind behavior. If ehandler is present, this proc is entered in the .xdata as the language specific handler. When the FRAME attribute is used, it must be followed by an .ENDPROLOG directive. If the function is a leaf function (as defined in Function Types) the FRAME attribute is unnecessary, as are the remainder of these pseudo-operations. |
| .PUSHREG reg | Generates a UWOP_PUSH_NONVOL unwind code entry for the specified register number using the current offset in the prologue. This should only be used with nonvolatile integer registers. For pushes of volatile registers, use an .ALLOCSTACK 8, instead |
| .SETFRAME reg, offset | Fills in the frame register field and offset in the unwind information using the specified register and offset. The offset must be a multiple of 16 and less than or equal to 240. This directive also generates a UWOP_SET_FPREG unwind code entry for the specified register using the current prologue offset. |
| .ALLOCSTACK size | Generates a UWOP_ALLOC_SMALL or a UWOP_ALLOC_LARGE with the specified size for the current offset in the prologue. The size operand must be a multiple of 8. |
| .SAVEREG reg, offset | Generates either a UWOP_SAVE_NONVOL or a UWOP_SAVE_NONVOL_FAR unwind code entry for the specified register and offset using the current prologue offset. MASM will choose the most efficient encoding. Offset must be positive, and a multiple of 8. Offset is relative to the base of the procedure’s frame, which is generally in RSP, or, if using a frame pointer, the unscaled frame pointer. |
| .SAVEXMM128 reg, offset | 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. MASM will choose the most efficient encoding. Offset must be positive, and a multiple of 16. Offset is relative to the base of the procedure’s frame, which is generally in RSP, or, if using a frame pointer, the unscaled frame pointer. |
| .PUSHFRAME [code] | Generates a UWOP_PUSH_MACHFRAME unwind code entry. If the optional code is specified, the unwind code entry is given a modifier of 1. Otherwise the modifier is 0. |
| .ENDPROLOG | Signals the end of the prologue declarations. Must occur in the first 255 bytes of the function. |
Here is a sample function prolog with proper usage of most of the opcodes:
sample PROC FRAME
db 048h; emit a REX prefix, to enable hot-patching
push rbp
.pushreg rbp
sub rsp, 040h
.allocstack 040h
lea rbp, [rsp+020h]
.setframe rbp, 020h
movdqa [rbp], xmm7
.savexmm128 xmm7, 020h;the offset is from the base of the frame
;not the scaled offset of the frame
mov [rbp+018h], rsi
.savereg rsi, 038h
mov [rsp+010h], rdi
.savereg rdi, 010h; you can still use RSP as the base of the frame
; or any other register you choose
.endprolog
; you can modify the stack pointer outside of the prologue (similar to alloca)
; because we have a frame pointer.
; if we didn’t have a frame pointer, this would be illegal
; if we didn’t make this modification,
; there would be no need for a frame pointer
sub rsp, 060h
; we can unwind from the following AV because of the frame pointer
mov rax, 0
mov rax, [rax] ; AV!
; restore the registers that weren’t saved with a push
; this isn’t part of the official epilog, as described in section 2.5
movdqa xmm7, [rbp]
mov rsi, [rbp+018h]
mov rdi, [rbp-010h]
; Here’s the official epilog
lea rsp, [rbp-020h]
pop rbp
ret
sample ENDP