Setting Machine-Level Breakpoints

To set a machine-level breakpoint, you must first display assembler code or source interleaved with assembler. (Refer to Examining Source and Assembler Code for information.) You can now select the tag field opposite an instruction. The tag field must contain a gridget--the gridget indicates the line is the beginning of a machine instruction. Since instruction sets on some platforms support variable-length instructions, you may see multiple lines associated with a single gridget. The icon appears, indicating that the breakpoint occurs before the instruction executes.

When the Source Pane displays source interleaved with assembler, source statements are treated as if they were comments: they are not treated as executable statements. (This is shown in the following figure.) Because they are treated as comments, you cannot set breakpoints on them. If you set a breakpoint on the first instruction after a source statement, however, you are actually creating a source-level breakpoint.

Breakpoint at Assembler Instruction

If you set machine-level breakpoints on one or more instructions that are part of a single source line and then display source code in the Source Pane, TotalView displays an icon on the line number. To see the specific breakpoints, you must display assembler or assembler interleaved with source code.

When a process reaches a breakpoint, TotalView:

• Suspends the process.
   
• Displays the PC arrow icon over the stop sign to indicate that the PC currently points to the breakpoint.
   

  Assembler and Source Interleaved

• Displays At Breakpoint in the Process Window title bar and other windows.
   
• Updates the Stack Trace and Stack Frame Panes and Variable Windows.