Re: [PATCH for-9.2 v3 0/6] target/sparc: emulate floating point queue when raising fp traps

[Carl Hauser]

Hi Richard,

I applied the 6 patches and then ran a divide-by-zero test on the Solaris image. The result was a crash

(qemu) qemu: fatal: Trap 0x08 (FPU Exception) while interrupts disabled, Error state
pc: f0066d80  npc: f0066d84
%g0-7: 00000000 01086002 00000000 00002000 00000000 fc067b80 00000001 f638b180
%o0-7: f025ef5c 00000000 00000000 f6376648 00000000 00000000 fc067b80 f004149c  
%l0-7: 04401087 00010a10 00010a14 fc067b80 fc067f70 00000080 00000001 fc067b80  
%i0-7: 00000000 01080000 00080000 00000002 0f800000 ef718cb0 effff510 000109ec  
%f00:  ffffffffffffffff ffffffffffffffff ffffffffffffffff ffffffffffffffff
%f08:  0000000040400000 ffffffffffffffff ffffffffffffffff ffffffffffffffff
%f16:  ffffffffffffffff ffffffffffffffff ffffffffffffffff ffffffffffffffff
%f24:  ffffffffffffffff ffffffffffffffff ffffffffffffffff ffffffffffffffff
psr: 04001087 (icc: ---- SPE: S--) wim: 00000002
fsr: 01090000 y: 00000000

I've seen that PC address before -- I'm pretty sure it is the STDFQ instruction in the kernel trap handler, and if I'm reading the fsr correctly that is confirmed by the fact that it is sequence-error type FPE which only occurs for STDFQ. Without a bit of further poking around with the debugger I don't know what's happening beyond that. I will keep looking but thought I'd provide immediate results in case this rings a bell for you.

If it would be helpful, I could share a disk image with Solaris, gnu tools, the test examples, etc. It's under 500MB compressed and I think I have enough google drive space to accommodate that at the moment.

-- Carl

On 8/16/24 00:23, Richard Henderson wrote:

> Hi Carl,
>
> While digging through the manual to figure out if we were really
> doing the right thing raising the fp exception, I found the fpu
> exception state machine.  I'm not sure it's worth emulating the
> fp_exception_pending state, but it's certainly easy enough to
> emulate the fp_executing/fp_exception states.
>
> In addition, this simplifies the implementation of STDFQ,
> restricts FQ to sparc32 system mode, and handles migration.
>
> Would you please double-check this against your Solaris images?
>
>
> r~
>
>
> Carl Hauser (2):
>   target/sparc: Add FQ and FSR.QNE
>   target/sparc: Populate sparc32 FQ when raising fp exception
>
> Richard Henderson (4):
>   target/sparc: Restrict STQF to sparcv9
>   target/sparc: Add FSR_QNE to tb_flags
>   target/sparc: Implement STDFQ
>   target/sparc: Add gen_trap_if_nofpu_fpexception
>
>  target/sparc/cpu.h          |  30 ++++++++-
>  target/sparc/fop_helper.c   |   4 ++
>  target/sparc/int32_helper.c |  32 ++++-----
>  target/sparc/machine.c      |  25 +++++++
>  target/sparc/translate.c    | 126 ++++++++++++++++++++++++++----------
>  target/sparc/insns.decode   |   4 +-
>  6 files changed, 169 insertions(+), 52 deletions(-)
>
>