Re: PROBLEM: 5.11.0-rc7 fails to compile with error: ‘-mindirect-branch’ and ‘-fcf-protection’ are not compatible

[Stuart Little]

And for good measure: reverting that commit 

20bf2b378729c4a0366a53e2018a0b70ace94bcd

flagged by the bisect right on top of the current tree compiles fine. 

On Sun, Feb 07, 2021 at 07:26:01PM -0500, Stuart Little wrote:
> The result of the bisect on the issue reported in the previous message:
> 
> --- cut ---
> 
> 20bf2b378729c4a0366a53e2018a0b70ace94bcd is the first bad commit
> commit 20bf2b378729c4a0366a53e2018a0b70ace94bcd
> Author: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
> Date:   Thu Jan 28 15:52:19 2021 -0600
> 
>     x86/build: Disable CET instrumentation in the kernel
>     
>     With retpolines disabled, some configurations of GCC, and specifically
>     the GCC versions 9 and 10 in Ubuntu will add Intel CET instrumentation
>     to the kernel by default. That breaks certain tracing scenarios by
>     adding a superfluous ENDBR64 instruction before the fentry call, for
>     functions which can be called indirectly.
>     
>     CET instrumentation isn't currently necessary in the kernel, as CET is
>     only supported in user space. Disable it unconditionally and move it
>     into the x86's Makefile as CET/CFI... enablement should be a per-arch
>     decision anyway.
>     
>      [ bp: Massage and extend commit message. ]
>     
>     Fixes: 29be86d7f9cb ("kbuild: add -fcf-protection=none when using retpoline flags")
>     Reported-by: Nikolay Borisov <nborisov@xxxxxxxx>
>     Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
>     Signed-off-by: Borislav Petkov <bp@xxxxxxx>
>     Reviewed-by: Nikolay Borisov <nborisov@xxxxxxxx>
>     Tested-by: Nikolay Borisov <nborisov@xxxxxxxx>
>     Cc: <stable@xxxxxxxxxxxxxxx>
>     Cc: Seth Forshee <seth.forshee@xxxxxxxxxxxxx>
>     Cc: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>
>     Link: https://lkml.kernel.org/r/20210128215219.6kct3h2eiustncws@treble
> 
>  Makefile          | 6 ------
>  arch/x86/Makefile | 3 +++
>  2 files changed, 3 insertions(+), 6 deletions(-)
> 
> --- end ---
> 
> On Sun, Feb 07, 2021 at 06:31:22PM -0500, Stuart Little wrote:
> > I am trying to compile on an x86_64 host for a 32-bit system; my config is at
> > 
> > https://termbin.com/v8jl
> > 
> > I am getting numerous errors of the form
> > 
> > ./include/linux/kasan-checks.h:17:1: error: ‘-mindirect-branch’ and ‘-fcf-protection’ are not compatible
> > 
> > and
> > 
> > ./include/linux/kcsan-checks.h:143:6: error: ‘-mindirect-branch’ and ‘-fcf-protection’ are not compatible
> > 
> > and
> > 
> > ./arch/x86/include/asm/arch_hweight.h:16:1: error: ‘-mindirect-branch’ and ‘-fcf-protection’ are not compatible
> > 
> > (those include files indicated whom I should add to this list; apologies if this reaches you in error).
> > 
> > The full log of the build is at
> > 
> > https://termbin.com/wbgs
> > 
> > ---
> > 
> > 5.11.0-rc6 built fine last week on this same setup.