User`s guide

Preparing to Port Macro-32 Code

1.5 Identifying Nonportable VAX MACRO Coding Practices

• Temporarily removing the return address from the stack to allocate space on

the stack using mechanisms such as the following (see Section 3.3.4):

POPL R0 ; remove the return address

SUBL #structure_size,SP ; allocate stack space for caller

PUSHL R0 ; replace the return address

POPL R1 ; hold return address

PUSHL structure ; build structure for caller

;

; code continues

;

JMP (R1) ; return to caller

• Pushing a label onto the stack, as in the following examples, often as

an attempt to construct a return address for an RSB instruction (see

Section 3.3.3):

MOVAL routine_label,-(SP)

RSB

PUSHAL routine_label

RSB

• Modifying the frame pointer (FP) (see Section 3.1.1). VAX MACRO code

typically modiﬁes the frame pointer for one of two reasons:

• To manually assemble a call frame on the stack.

• To use the frame pointer to reference local storage allocated in a .JSB_

ENTRY routine.

MOVL SP,FP

SUBL #data_area,SP

• Constructing an REI target, as in the following examples (see Section 3.3.7):

MOVL #fake_psl,-(SP)

MOVAL target_label,-(SP) ; all three

REI

MOVPSL -(SP)

MOVAL target_label,-(SP) ; force AST delivery only

REI

MOVL #fake_psl,-(SP)

BSBW DOREI

;

; code continues

;

DOREI: REI

• Branching to a destination that consists of a label plus an offset as in the

following example. The appearance of this practice in VAX MACRO code

might indicate a branch past some data in the code stream, such as the

Alternatively, it might be a sign that the code is familiar with and dependent

upon the size of VAX instructions (see Section 3.2.3):

Preparing to Port Macro-32 Code 1–7