* Re: [Patch ,gcc/MIPS] add an build-time/runtime option to disable madd.fmt
[not found] ` <6BFA91F2-1B3B-422C-AD1C-D6F4A00D625A@imgtec.com>
@ 2017-01-11 17:40 ` Maciej W. Rozycki
2017-01-11 17:40 ` Maciej W. Rozycki
0 siblings, 1 reply; 2+ messages in thread
From: Maciej W. Rozycki @ 2017-01-11 17:40 UTC (permalink / raw)
To: Yunqiang Su
Cc: Paul Hua, Richard Sandiford, Matthew Fortune, Sandra Loosemore,
gcc-patches, Moore, Catherine (Catherine_Moore@mentor.com),
huangpei, linux-mips
On Fri, 23 Dec 2016, Yunqiang Su wrote:
> > 3, kernel: the emulation when a float exception taken.
>
> The big problem is that Loongson use the same encode for (unfused)
> madd.fmt to (fused) madd.fmt. We cannot trap this in kernel.
Why is that a problem? Just add a setting like `cpu_has_fused_madd' to
<asm/cpu-features.h>, switch processing in the emulator accordingly and
initialise the setting early on in bootstrap as processor features are
determined. We'd have to do it likewise for the R8000 MIPS IV CPU Richard
referred to previously if we had full support for this processor (unlikely
to happen).
Cc-ing <linux-mips@linux-mips.org> in case you want to discuss it further
with the kernel developers; arguably it's a kernel bug already that the
FPU as perceived by user software has different semantics on FPU Loongson
hardware depending on whether or not the `nofpu' kernel parameter has been
set (I don't know if denormals are handled by Loongson FPU hardware or
trap with an Unimplemented Operation exception, but if the former, then
this inconsistency applies for such data in the regular FPU mode as well).
HTH,
Maciej
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: [Patch ,gcc/MIPS] add an build-time/runtime option to disable madd.fmt
2017-01-11 17:40 ` [Patch ,gcc/MIPS] add an build-time/runtime option to disable madd.fmt Maciej W. Rozycki
@ 2017-01-11 17:40 ` Maciej W. Rozycki
0 siblings, 0 replies; 2+ messages in thread
From: Maciej W. Rozycki @ 2017-01-11 17:40 UTC (permalink / raw)
To: Yunqiang Su
Cc: Paul Hua, Richard Sandiford, Matthew Fortune, Sandra Loosemore,
gcc-patches, Moore, Catherine (Catherine_Moore@mentor.com),
huangpei, linux-mips
On Fri, 23 Dec 2016, Yunqiang Su wrote:
> > 3, kernel: the emulation when a float exception taken.
>
> The big problem is that Loongson use the same encode for (unfused)
> madd.fmt to (fused) madd.fmt. We cannot trap this in kernel.
Why is that a problem? Just add a setting like `cpu_has_fused_madd' to
<asm/cpu-features.h>, switch processing in the emulator accordingly and
initialise the setting early on in bootstrap as processor features are
determined. We'd have to do it likewise for the R8000 MIPS IV CPU Richard
referred to previously if we had full support for this processor (unlikely
to happen).
Cc-ing <linux-mips@linux-mips.org> in case you want to discuss it further
with the kernel developers; arguably it's a kernel bug already that the
FPU as perceived by user software has different semantics on FPU Loongson
hardware depending on whether or not the `nofpu' kernel parameter has been
set (I don't know if denormals are handled by Loongson FPU hardware or
trap with an Unimplemented Operation exception, but if the former, then
this inconsistency applies for such data in the regular FPU mode as well).
HTH,
Maciej
^ permalink raw reply [flat|nested] 2+ messages in thread
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2017-01-11 17:40 ` [Patch ,gcc/MIPS] add an build-time/runtime option to disable madd.fmt Maciej W. Rozycki
2017-01-11 17:40 ` Maciej W. Rozycki
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