Hi Marcelo,

Yes, gem5 does support the C extension (64-bit version only, though).  I
don't know what could be causing your particular issue.  I'm not sure
advancePC is the issue, though, because all that essentially does is call
PCState::advance(), which is inherited unchanged from
GenericISA::UPCState.  Try doing as Jason suggests and run your simulation
with the Fetch debug flag enabled, and maybe that will shed some light on
the issue.


On Thu, May 24, 2018 at 7:20 PM, Jason Lowe-Power <ja...@lowepower.com>

> Hi Marcelo,
> I'm not sure if RISC-V has been tested with the out of order CPU at all!
> I'm happy that at least it doesn't completely fail!
> For you problem of only fetching 1 instruction per cycle... I think it's
> going to take some digging. My first guess would be that it could be a
> problem with the advancePC() function that's implemented in the RISC-V
> decoder (in gem5/arch/riscv), but I don't really have any specific reason
> to think that :).
> You could try turning on some debug flags for the O3 CPU. Specifically,
> Fetch might be helpful.
> Cheers,
> Jason
> On Thu, May 24, 2018 at 4:06 PM Marcelo Brandalero <
> mbrandal...@inf.ufrgs.br> wrote:
>> Hi all,
>> I recently switched from gem5/x86 to gem5/RISCV due to some advantages of
>> this ISA.
>> I'm getting some weird simulation results and I realized my compiler was
>> generating instructions for the compressed RISCV ISA extension (chp 12
>> in the user level ISA specification <https://riscv.org/specifications/>).
>> The weirdness disappears when I use *--march* to remove these extensions.
>> *So the question is: does gem5/RISCV support this ISA extension? *If so,
>> I can share the weird results (maybe I'm missing something) but basically a
>> wide-issue O3 processor fetches only max 1 instruction/cycle when it should
>> probably be fetching more.
>> If it doesn't support then it's all OK, I just find it a bit weird that
>> the program executes normally with no warnings whatsoever.
>> Best regards,
>> --
>> Marcelo Brandalero
>> PhD Candidate
>> Programa de Pós Graduação em Computação
>> Universidade Federal do Rio Grande do Sul
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