Re: [PATCH v9] MIPS: force use FR=0 for FPXX binaries

[Thomas Bogendoerfer <tsbogend@alpha.franken.de>]

On Mon, Mar 29, 2021 at 06:28:40PM +0800, YunQiang Su wrote:
> Thomas Bogendoerfer <tsbogend@alpha.franken.de> 于2021年3月29日周一 下午5:30写道：
> >
> > On Mon, Mar 29, 2021 at 01:09:18PM +0800, YunQiang Su wrote:
> > > YunQiang Su <yunqiang.su@cipunited.com> 于2021年3月22日周一 上午10:00写道：
> > > >
> > > > The MIPS FPU may have 3 mode:
> > > >   FR=0: MIPS I style, all of the FPR are single.
> > > >   FR=1: all 32 FPR can be double.
> > > >   FRE: redirecting the rw of odd-FPR to the upper 32bit of even-double FPR.
> > > >
> > > > The binary may have 3 mode:
> > > >   FP32: can only work with FR=0 and FRE mode
> > > >   FPXX: can work with all of FR=0/FR=1/FRE mode.
> > > >   FP64: can only work with FR=1 mode
> > > >
> > > > Some binary, for example the output of golang, may be mark as FPXX,
> > > > while in fact they are FP32. It is caused by the bug of design and linker:
> > > >   Object produced by pure Go has no FP annotation while in fact they are FP32;
> > > >   if we link them with the C module which marked as FPXX,
> > > >   the result will be marked as FPXX. If these fake-FPXX binaries is executed
> > > >   in FR=1 mode, some problem will happen.
> > > >
> > > > In Golang, now we add the FP32 annotation, so the future golang programs
> > > > won't have this problem. While for the existing binaries, we need a
> > > > kernel workaround.
> > > >
> > >
> > > We meet a new problem in Debian: with the O32_FP64 enabled kernel,
> > > mips64el may also be affected.
> > > https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=983583
> >
> > hmm, raising this issue in this context before knowing more details,
> > feels very trigger happy to me and this doesn't help accepting anything,
> > jfyi...
> >
> > Could you please provide a link for downloading a golang binary, which
> > would need this patch to run ?
> >
> 
> For rootfs, you can download
>    http://58.246.137.130:20180/debian-from/rootfs/buster-mipsel.tar.xz
> or create by:
>     sudo debootstrap --arch mipsel  --include golang-1.11-go \
>                      buster buster-mipsel http://deb.debian.org/debian
> 
> For binary packages, you can download:
>     https://packages.debian.org/buster/mipsel/golang-1.11-go/download
> 
> just chroot the rootfs and run:
>     /usr/lib/go-1.11/bin/go
> It will crash if kernel's O32_FP64 option is enabled.

now I'm confused. Do go binaries crash the kernel ? Or is this just
the issue _not_ related to this patch ?

I want a single go binary, which I can inspect about the FPXX thing and
see how easy it would be to just patch the binary and make it run without
this patch.

Thomas.

-- 
Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
good idea.                                                [ RFC1925, 2.3 ]