Книга: Embedded Linux Primer: A Practical, Real-World Approach

15.4.3. Debugging Bootloader/Flash Code

15.4.3. Debugging Bootloader/Flash Code

Debugging Flash resident code presents its own unique challenges. The most obvious limitation is the way in which GDB and gdbserver cooperate in setting target breakpoints. When we discussed the GDB remote serial protocol in Chapter 14, you learned how breakpoints are inserted into an application.[104] GDB replaces the opcode at the breakpoint location with an architecture-specific opcode that passes control to the debugger. However, in ROM or Flash, GDB cannot overwrite the opcode, so this method of setting breakpoints is useless.

Most modern processors contain some number of debug registers that can be used to get around this limitation. These capabilities must be supported by architecture-and processor-specific hardware probes or stubs. The most common technique for debugging Flash and ROM resident code is to use JTAG hardware probes. These probes support the setting of processor-specific hardware breakpoints. This topic was covered in detail in Chapter 14. Refer back to Section 14.4.2, "Debugging with a JTAG Probe," for details.

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