Le 25/01/2022 à 04:04, Nicholas Piggin a écrit :

+Naveen (sorry missed cc'ing you at first)

Excerpts from Christophe Leroy's message of January 24, 2022 4:39 pm:

quoted

Le 24/01/2022 à 06:57, Nicholas Piggin a écrit :

quoted

As discussed previously

https://lists.ozlabs.org/pipermail/linuxppc-dev/2022-January/238946.html

I'm wondering whether PPC32 should be returning -1 for syscall
instructions too here? That could be done in another patch anyway.

The 'Programming Environments Manual for 32-Bit Implementations of the
PowerPC™ Architecture' says:

The following are not traced:
• rfi instruction
• sc and trap instructions that trap
• Other instructions that cause interrupts (other than trace interrupts)
• The first instruction of any interrupt handler
• Instructions that are emulated by software


So I think PPC32 should return -1 as well.

I agree.

What about the trap instructions? analyse_instr returns 0 for them
which falls through to return 0 for emulate_step, should they
return -1 as well or am I missing something?

For the traps I don't know. The manual says "trap instructions that 
trap" are not traced. It means that "trap instructions that _don't_ 
trap" are traced. Taking into account that trap instructions don't trap 
at least 99.9% of the time, not sure if returning -1 is needed.

Allthought that'd probably be the safest.

But then what happens with other instruction that will sparsely generate 
an exception like a DSI or so ? If we do it for the traps then we should 
do it for this as well, and then it becomes a non ending story.

So at the end it's probably ok with return 0, both for them and for traps.

Christophe