- I am trying to debug Linux on an IBM 405GP
processor. Linux boots fine and I can step through the code until
head_4xx.S; then I get the following:
- TARGET: target has entered debug mode Target state : debug mode Debug entry cause : JTAG stop request Current PC : 0x00000700 Current CR : 0x28004088 Current MSR : 0x00000000 Current LR : 0x000007a8 # Step timeout detected
- Your single step problem most likely comes from
the fact that GDB accesses some non-existent memory
(at least some versions do/did in the past).
This exception is stored in some way
within the 405 and when you step
"rfi"it triggers. This is because some instructions like
"rfi"are always stepped using a hardware breakpoint and not with the JTAG single step feature. Probably you can step over the
"rfi"instruction when using the BDI2000's
telnetcommand interface instead of GDB. Similar problems have also been reported when stepping through
"mfmsr"during initial boot code. The problem comes also from the fact that GDB accesses non-existent memory (maybe it tries to read a non-existent stack frame). To debug the Linux kernel, I recommend that you run to a point where the MMU is on before you connect with GDB. To debug boot code where the MMU is off I recommend to use the MMAP feature of the BDI to prevent illegal memory accesses from GDB.
|14.6.2. How to Debug Linux Exceptions||1. Abstract||14.6.4. Setting a breakpoint doesn't work|