Debug exception in tRootTask in VxWorks

Question

Using VxWorks A653 v2.5.0.2 I am getting an exception being generated in tRootTask during startup:

data storage
Exception current instruction address: 0x50000120
Machine Status Register: 0x0000fb30
Data Exception Address Register: 0x00000008
Integer Exception Register XER: 0x00000000
Condition Register: 0x40000088
Exception Syndrome Register: 0x01000000
Partition Domain ID: 0x007539a0
Task: 0x521f5920 "tRootTask"

the tRootTask does spawn a number of other kernel tasks and also creates a task for the user partition. But the entry point to the user task in the user partition never seems to run (printf() statement is not hit). After the exception occurs it is possible to attach a debugger, but the tRootTask itself is deleted by the exception. If I access the shell after the exception, attempting to display the contents at 0x50000000 contains fails, as if it is unmapped memory. This may be the root cause of the exception, but why it's inaccessible is unclear.

So I am searching for a way to debug why the exception is happening. I'm new to this OS.itself

Answer 1

Look in your linker map for the "Exception current instruction address: 0x50000120"

Or if the shell has "lkup" -> lkup 0x50000120

should give the nearest global function that's throwing exception.
Data Exception Address Register: 0x00000008 looks like zero page access, but you need decipher the "Exception Syndrome Register" in PowerPC manual to see if it's the right condition code?

"tRootTask" is the first thread in the context, so it's some sort of startup code that's failing. But it's so early, you probably need a JTAG debugger to get a breakpoint on it.