Problems with turn_on_mmu

Gabriel Paubert paubert at
Fri Jan 26 19:14:02 EST 2001

On Thu, 25 Jan 2001, Subodh Nijsure wrote:

> 1. I am novice in PowerPC assembler code ( yes doing the RTFM) Why does gdb
> hang when
>    I do 'stepi' on instruction rfi ?

Because rfi is impossible to trace: actually any instruction between the
setting of srr0/srr1 and rfi cannot be traced because the trace exception
destroys srr0 and srr1. A smart debugger would check for mtsrr0/mtsrr1/rfi
while single stepping, cache srr0/srr1 and emulate rfi. I've not yet
encountered a debugger which does this, and a bulletproof implementation
is impossible, i.e., you can't set a breakpoint between mtsrr0/mtsrr1 and
rfi and expect it to work.


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