Phase Errors May Be Caused By Forward References

• Microsoft Macro Assembler for MS-DOS, versions 1.25, 1.27, 3.0x, 4.0, 5.0, and 5.1

SUMMARY

Phase errors indicate that a relative address of a label changed between pass 1 and pass 2 of the assembly process. They usually are caused by improper forward references to labels. During pass 1, the assembler will have to make assumptions (e.g. it might assume a near jump during pass 1 if the location of a label is not known). During pass 2, the assembler may have to change those assumptions (e.g. now it knows that the jump is to a far label). If this involves changing the size of an instruction, that difference can cause a phase error.

To examine the assumptions made by the assembler on pass 1, use the /D option to get a pass 1 listing.

MORE INFORMATION

Phase errors can usually be prevented by using segment overrides or explicit type specification, as shown in the following examples:

   jmp dword ptr far_label         ;jump to far label

   mov ax, word ptr label