[Bug 1939379] Re: ARM kernel builds fail with GCC 11

[Dimitri John Ledkov]

@juerg

>From your autopkgtest result:

Building module:
cleaning build area...
make -j4 KERNELRELEASE=5.13.0-1006-raspi -C /lib/modules/5.13.0-1006-raspi/build M=/var/lib/dkms/adv-17v35x/5.0.6.0-1/build....
cleaning build area...

DKMS: build completed.

Building module:
cleaning build area...
make -j4 KERNELRELEASE=5.13.0-14-generic -C /lib/modules/5.13.0-14-generic/build M=/var/lib/dkms/adv-17v35x/5.0.6.0-1/build....(bad exit status: 2)
Error! Bad return status for module build on kernel: 5.13.0-14-generic (armv7l)

Because the toolchain fix was only applied in the linux-raspi flavour so far
, and not generic.

I.e. gcc-11 did not migrate, and "UBUNTU: SAUCE: arm: Fix instruction
set selection for GCC 11" is not in generic kernel, yet.

so it is expected that dkms builds for generic kernel fail on armhf with
gcc-11 from impish-release.

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https://bugs.launchpad.net/bugs/1939379

Title:
  ARM kernel builds fail with GCC 11

Status in gcc-11 package in Ubuntu:
  Confirmed
Status in gcc-defaults package in Ubuntu:
  Invalid

Bug description:
  While this might be a kernel build problem (see LP: #1939308) I wanted
  to raise the issue against the toolchain just so we can make sure it's
  *not* a toolchain bug. Basically the following behavior changed from
  gcc 10:

  $ arm-linux-gnueabihf-gcc-10 -march=armv7-a -c -x c /dev/null ; echo $?
  0

  $ arm-linux-gnueabihf-gcc-11 -march=armv7-a -c -x c /dev/null ; echo $?
  cc1: error: ‘-mfloat-abi=hard’: selected architecture lacks an FPU
  1

  Presumably the GCC 11 hard-float compiler now enforces the default
  config --with-float=hard?

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