| Message ID | 20241025141254.2141506-1-peter.maydell@linaro.org |
|---|---|
| Headers | show |
| Series | softfloat: Set 2-NaN propagation rule in float_status, not at compile time | expand |
On 10/25/24 16:12, Peter Maydell wrote: > A summary of those TODOs and other oddities I have noticed but not > tried to tackle is:> > * hppa really ought to implement a CPU reset method > * alpha also doesn't implement CPU reset I used the alpha code as template to implement the hppa machine. That's probably why the CPU reset method is missing for both :-) The TODO about implementing: ? resettable_class_set_parent_phases(rc, NULL, hppa_cpu_reset_hold, NULL,...)... Helge
On Fri, 25 Oct 2024 at 15:49, Helge Deller <deller@gmx.de> wrote: > > > On 10/25/24 16:12, Peter Maydell wrote: > > A summary of those TODOs and other oddities I have noticed but not > > tried to tackle is:> > > * hppa really ought to implement a CPU reset method > > * alpha also doesn't implement CPU reset > > I used the alpha code as template to implement the hppa machine. > That's probably why the CPU reset method is missing for both :-) > > The TODO about implementing: ? > resettable_class_set_parent_phases(rc, NULL, hppa_cpu_reset_hold, NULL,...)... Yes, basically. The reset method should restore all the state of the CPU to what it was when QEMU started. Typically you put an end_reset_fields marker in the CPU state struct so you can memset() everything up to that point to zero, and then manually reset anything else that needs special handling. thanks -- PMM
On 10/25/24 16:59, Peter Maydell wrote: > On Fri, 25 Oct 2024 at 15:49, Helge Deller <deller@gmx.de> wrote: >> >> >> On 10/25/24 16:12, Peter Maydell wrote: >>> A summary of those TODOs and other oddities I have noticed but not >>> tried to tackle is:> >>> * hppa really ought to implement a CPU reset method >>> * alpha also doesn't implement CPU reset >> >> I used the alpha code as template to implement the hppa machine. >> That's probably why the CPU reset method is missing for both :-) >> >> The TODO about implementing: ? >> resettable_class_set_parent_phases(rc, NULL, hppa_cpu_reset_hold, NULL,...)... > > Yes, basically. The reset method should restore all the > state of the CPU to what it was when QEMU started. > Typically you put an end_reset_fields marker in the > CPU state struct so you can memset() everything up to > that point to zero, and then manually reset anything > else that needs special handling. Thanks for the explanation! I've just sent a patch to the mailing list: [PATCH] target/hppa: Add CPU reset method I tested it and it does work for me. If OK for you, I'd happy if you could include it in your patch series and adjust as needed to fix the FP initialization. Helge
IEEE 758 does not define a fixed rule for which NaN to pick as the result if both operands of a 2-operand operation are NaNs. As a result different architectures have ended up with different rules for propagating NaNs. QEMU currently hardcodes the NaN propagation logic into the binary, because pickNaN() has an ifdef ladder for different targets. We want to make the propagation rule instead be selectable at runtime, because: * this will let us have multiple targets in one QEMU binary * the Arm FEAT_AFP architectural feature includes letting the guest select a NaN propagation rule at runtime * x86 specifies different propagation rules for x87 FPU ops and for SSE ops, and specifying the rule in the float_status would let us emulate this, instead of wrongly using the x87 rules everywhere * xtensa allows selection of NaN propagation rule at runtime; currently we implement this with the use_first_nan flag which is only used by xtensa; providing a general facility will let us remove this limited-purpose handling This series switches pickNaN away from the ifdef ladder. Instead targets must always set a 2-NaN propagation rule via the new set_float_2nan_prop_rule(), unless they are using default_nan_mode. Patch 1 implements this in core softfloat (with a transitional fallback to "use the old ifdef ladder logic" if the target doesn't specify the propagation rule). Then subsequent patches convert all the targets to set the rule explicitly. The final patch then removes the remnants of the transitional logic. I have included a couple of minor fixes for sparc, xtensa, m68k. This is intended as a no-behaviour-change patchset, so although there are a few places where I have noticed that the current behaviour is not correct I have left these as TODO comments. A summary of those TODOs and other oddities I have noticed but not tried to tackle is: * hppa really ought to implement a CPU reset method * alpha also doesn't implement CPU reset * ppc sets tininess_before_rounding on fp_status but not on vec_status, so its behaviour there will vary between guest instructions; unclear to me if this is intended * x86 should set the float_2nan_prop_ab rule on env->sse_status (and maybe env->mmx_status, though 3DNow! insns don't handle NaNs in a documented way anyway) * alpha never had a case in the ifdef ladder so it uses the x87 propagation rule. It ought to use float_2nan_prop_ba. * openrisc didn't have an ifdef and also uses the x87 rule; this is probably wrong but I couldn't find anything documenting what it actually does * rx didn't have an ifdef and also uses the x87 rule; again, probably wrong The next stage after this patchset, obviously, is to do the same thing with pickNaNMulAdd(). That is a little trickier because currently we ask it to do two things: * handle the "infinity * zero + NaN" corner case * pick a NaN when more than one operand is a NaN My intention is to separate these out so that targets specify both separately. This gives more orthogonality (e.g. Arm, MIPS with !snan_bit_is_one and loongarch64 all have the same "prefer SNaN over QNaN, prefer C over A over B" NaN selection logic but they have different ideas about the infzero case). (Once pickNaNMulAdd() is converted we will be able to remove the current xtensa-specific use_first_nan flag.) thanks -- PMM Peter Maydell (21): softfloat: Allow 2-operand NaN propagation rule to be set at runtime tests/fp: Explicitly set 2-NaN propagation rule target/arm: Explicitly set 2-NaN propagation rule target/mips: Explicitly set 2-NaN propagation rule target/loongarch: Explicitly set 2-NaN propagation rule target/hppa: Explicitly set 2-NaN propagation rule target/s390x: Explicitly set 2-NaN propagation rule target/ppc: Explicitly set 2-NaN propagation rule target/m68k: Explicitly set 2-NaN propagation rule target/m68k: Initialize float_status fields in gdb set/get functions target/sparc: Move cpu_put_fsr(env, 0) call to reset target/sparc: Explicitly set 2-NaN propagation rule target/xtensa: Factor out calls to set_use_first_nan() target/xtensa: Explicitly set 2-NaN propagation rule target/i386: Set 2-NaN propagation rule explicitly target/alpha: Explicitly set 2-NaN propagation rule target/microblaze: Move setting of float rounding mode to reset target/microblaze: Explicitly set 2-NaN propagation rule target/openrisc: Explicitly set 2-NaN propagation rule target/rx: Explicitly set 2-NaN propagation rule softfloat: Remove fallback rule from pickNaN() include/fpu/softfloat-helpers.h | 11 +++ include/fpu/softfloat-types.h | 38 ++++++++ target/i386/cpu.h | 3 + target/mips/fpu_helper.h | 22 +++++ target/xtensa/cpu.h | 6 ++ linux-user/arm/nwfpe/fpa11.c | 18 ++++ target/alpha/cpu.c | 11 +++ target/arm/cpu.c | 25 +++-- target/hppa/fpu_helper.c | 6 ++ target/i386/cpu.c | 4 + target/i386/tcg/fpu_helper.c | 40 ++++++++ target/loongarch/tcg/fpu_helper.c | 1 + target/m68k/cpu.c | 16 +++ target/m68k/fpu_helper.c | 1 + target/m68k/helper.c | 4 +- target/microblaze/cpu.c | 10 +- target/mips/cpu.c | 2 +- target/mips/msa.c | 17 ++++ target/openrisc/cpu.c | 6 ++ target/ppc/cpu_init.c | 8 ++ target/rx/cpu.c | 7 ++ target/s390x/cpu.c | 1 + target/sparc/cpu.c | 10 +- target/sparc/fop_helper.c | 10 +- target/xtensa/cpu.c | 2 +- target/xtensa/fpu_helper.c | 35 ++++--- tests/fp/fp-bench.c | 2 + tests/fp/fp-test-log2.c | 1 + tests/fp/fp-test.c | 2 + fpu/softfloat-specialize.c.inc | 156 +++++++++++------------------- 30 files changed, 346 insertions(+), 129 deletions(-)