On Mon, Mar 29, 2021 at 06:28:40PM +0800, YunQiang Su wrote:

Thomas Bogendoerfer [off-list ref] 于2021年3月29日周一 下午5:30写道：

quoted

On Mon, Mar 29, 2021 at 01:09:18PM +0800, YunQiang Su wrote:

quoted

YunQiang Su [off-list ref] 于2021年3月22日周一 上午10:00写道：

quoted

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 ]