Microsoft KB Archive/49900

= PRB: Jumping to an Absolute Address with MASM =

Article ID: 49900

Article Last Modified on 10/17/2003

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APPLIES TO


 * Microsoft Macro Assembler 5.0
 * Microsoft Macro Assembler 5.1 Standard Edition
 * Microsoft Macro Assembler 5.1a
 * Microsoft Macro Assembler 6.0 Standard Edition
 * Microsoft Macro Assembler 6.0a
 * Microsoft Macro Assembler 6.0b

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This article was previously published under Q49900



SYMPTOMS
The Microsoft Macro Assembler (MASM) will not let you jump directly to a hexadecimal address. If you try to assemble: jmp 0FFFFh:0000h You will receive the error message:

A2038: left operand must have segment



CAUSE
This is the expected behavior for MASM. To make a jump to an absolute address you must create a pointer to point to the offset inside of the segment.



RESOLUTION
To create a pointer to point to the offset inside of the segment in question you would create a segment at a specific location. For example: bios SEGMENT AT 0FFFFh ORG 0 reset LABEL FAR bios ENDS Then, any one of the following three jump instructions will perform the jump to offset 0000h within segment FFFFh: jmp FAR PTR reset jmp bios:reset jmp reset Note that the opcode that is generated in the listing file is EA 0000



MORE INFORMATION
This process is covered on Page 101 of the &quot;Microsoft Macro Assembler 5.0: Programmer's Guide.&quot; The second paragraph states the following:

An AT segment typically contains no code or initialized data. Instead, it represents an address template that can be placed over code or data already in memory, such as a screen buffer or other absolute memory locations defined by hardware. The linker will not generate any code or data for AT segments, but existing code or data can be accessed by name if it is given a label in an AT segment.

Additional query words: 5.00 5.10 5.10a 6.00 6.00a 6.00b bios rom

Keywords: KB49900

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