Re: [gentoo-user] kernel 4.9.77 error segfault in compile.

[Corbin Bird]

On 01/23/2018 11:35 AM, Rich Freeman wrote:
> Abandoning ext4 over retpolines/etc seems a bit drastic.  My guess is
> that there is a bug in the latest kernel that will get fixed, or maybe
> a bug in gcc (which needs to be patched for spectre anyway).
>
> These Spectre changes are being merged and it has been a real mess.
> The vulnerability is relatively serious so there is a lot of pressure
> to do something, but the changes aren't trivial so they could contain
> bugs or expose compiler bugs.
>
> FWIW upstream 4.9.77 builds just fine for me,
>
> If you want to mess with building alternate kernels to debug this here
> are some instructions I created for this:
>
> As a test you might consider the following:
>
> mkdir /someplace
> cd /someplace
> git clone -b linux-4.9.y
> git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git
> .
> mkdir /var/tmp/linux
> cp /path/to/config /var/tmp/linux/.config
> make O=/var/tmp/linux oldconfig
> make O=/var/tmp/linux -j#
>
> That will build the latest stable upstream kernel.
>
> Depending on what you find you can do:
> git checkout v4.9.76
> rm -r /var/tmp/linux
> mkdir /var/tmp/linux
> cp /path/to/config /var/tmp/linux/.config
> make O=/var/tmp/linux oldconfig
> make O=/var/tmp/linux -j#
>
> That will see if 4.9.76 fails.  You could also substitute any version
> you want (including a 4.14 kernel, or an earlier 4.9 kernel).  This
> will give you a sense of whether your toolchain is just entirely
> broken, or if there is an issue with the objtool changes.
>
> Note that you can build away as much as you want without having to
> install any of this - so it won't affect your system at all.  In fact,
> the instructions above will work just fine if you run them as
> non-root, as long as you clone the git sources and put the temp
> directory someplace your non-root user has access to.
>

Tried this ... and here are the steps followed and results :
Note :
CPU defined as K8, NO vendor support for Intel or Centaur, AMD only.
gcc && binutils are both current stable, both r1's. Tested and working.
Both Disabled in 'menuconfig' :
>  [ ] Avoid speculative indirect branches in kernel
>  [ ] Remove the kernel mapping in user mode
The steps followed :
-----
mkdir /opt/compile
cd /opt/compile
git clone -b linux-4.9.y
git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git
renamed 'linux-stable' to 'linux-4.9.77'
ln -s /opt/compile/linux-4.9.77 linux
cd /opt/compile/linux
make menuconfig
mkdir /var/tmp/linux
cp /opt/compile/linux/.config /var/tmp/linux/.config
make O=/var/tmp/linux oldconfig
make O=/var/tmp/linux -j9
-----
The results ( first pass ) :

>   HOSTCC  arch/x86/tools/relocs_64.o
>   HOSTCC  arch/x86/tools/relocs_common.o
>   Using /opt/compile/linux-4.9.77 as source for kernel
>   /opt/compile/linux-4.9.77 is not clean, please run 'make mrproper'
>   in the '/opt/compile/linux-4.9.77' directory.
> make[1]: *** [/opt/compile/linux-4.9.77/Makefile:1021: prepare3] Error 1
> make[1]: *** Waiting for unfinished jobs....
>   HOSTLD  arch/x86/tools/relocs
> make[1]: Leaving directory '/var/tmp/linux'
> make: *** [Makefile:150: sub-make] Error 2

So ... I ran 'make mrproper' in '/opt/compile/linux-4.9.77/'
The result :

>   HOSTCC  arch/x86/tools/relocs_64.o
>   HOSTCC  arch/x86/tools/relocs_common.o
>   Using /opt/compile/linux-4.9.77 as source for kernel
>   /opt/compile/linux-4.9.77 is not clean, please run 'make mrproper'
>   in the '/opt/compile/linux-4.9.77' directory.
> make[1]: *** [/opt/compile/linux-4.9.77/Makefile:1021: prepare3] Error 1
> make[1]: *** Waiting for unfinished jobs....
>   HOSTLD  arch/x86/tools/relocs
> make[1]: Leaving directory '/var/tmp/linux'
> make: *** [Makefile:150: sub-make] Error 2

Something is not right ....
  HOSTCC  arch/x86/tools/relocs_64.o
  HOSTCC  arch/x86/tools/relocs_common.o
  HOSTLD  arch/x86/tools/relocs
Is this the 'Spectre/Meltdown' patches again?!?

Corbin