PRB: Incorrect Debug Information in 32-bit Object Module

• Microsoft Macro Assembler for Windows NT, version 6.1

SYMPTOMS

When you step through assembly source code with a debugger, instructions do not seem to execute properly. Switching to mixed assembly and source shows the source code does not match up with the disassembled code.

CAUSE

When you debug a Windows NT application containing an Object Module Format (OMF) object module created with Microsoft Macro Assembler (MASM), version 6.1, the source line number debug information is incorrect when converted to Common Object File Format (COFF) by a 32-bit linker (such as the linker shipped with Microsoft Visual C++, 32-bit edition). This results in lines in the source file being incorrectly associated with points in the executable file.

RESOLUTION

Assemble the assembly source file using the /coff switch, which will cause MASM to generate a COFF object module.

MORE INFORMATION

COFF is the preferred object file format for Windows NT, and you should always use the /coff switch when assembling source files for use in the Windows NT operating system.