On Tue, 11 Aug 2020 at 14:33, Gustavo Romero <grom...@linux.vnet.ibm.com> wrote: > On 8/11/20 6:31 AM, Peter Maydell wrote: > > You don't want to call gen_io_end; you just need to ensure that > > you end the TB immediately after this insn. See > > docs/devel/tcg-icount.rst. > > I understand that to ensure that TB ends immediately after these > instructions (I understood you meant all the cases, not just the > spr_read_purr case, right?), the instructions should be a branch > or change CPU state in a way that cannot be deduced at translation > time, and I don't know how to ensure that in these cases, they > are neither, specially for the read access, which doesn't change > any CPU state specifically afaics.
No, you have that the wrong way around. *If* an instruction is a branch or a state-changing one, *then* it must end the TB. That doesn't mean that *only* those kinds of insn can end the TB -- other things also can end a TB. (It also doesn't mean that a branch etc will automatically end the TB -- it means that if you're writing the bit of target code that generates code for a branch/etc then you must specifically ensure that you end the TB.) > If I remove the gen_io_end() from all these cases the VM gets > stuck at apparently random points of execution (I'm digging > into details right now trying to understand why). Probably because you're not ending the TB after the insn. PowerPC seems to be doing something slightly weird in this area -- it classifies "stop translation" as a kind of exception (POWERPC_EXCP_STOP) rather than just using the common-code is_jmp machinery and setting it to DISAS_EXIT. So you'll need a ppc expert to say what the right thing is, but my guess is you want to call gen_stop_exception() -- compare gen_darn(). thanks -- PMM
