Re: [PATCH v23 6/9] x86/entry: Introduce ENDBR macro

[Yu, Yu-cheng]

On 3/16/2021 1:15 PM, Peter Zijlstra wrote:
> On Tue, Mar 16, 2021 at 01:05:30PM -0700, Yu, Yu-cheng wrote:
> > On 3/16/2021 12:57 PM, Peter Zijlstra wrote:
> > > On Tue, Mar 16, 2021 at 10:12:39AM -0700, Yu, Yu-cheng wrote:
> > > > Alternatively, there is another compiler-defined macro _CET_ENDBR that can
> > > > be used.  We can put the following in calling.h:
> > > >
> > > > #ifdef __CET__
> > > > #include <cet.h>
> > > > #else
> > > > #define _CET_ENDBR
> > > > #endif
> > > >
> > > > and then use _CET_ENDBR in other files.  How is that?
> > > >
> > > > In the future, in case we have kernel-mode IBT, ENDBR macros are also needed
> > > > for other assembly files.
> > >
> > > Can we please call it IBT_ENDBR or just ENDBR. CET is a horrible name,
> > > seeing how it is not specific.
> >
> > _CET_ENDBR is from the compiler and we cannot change it.  We can do:
> >
> > #define ENDBR _CET_ENDBR
> >
> > How is that?
>
> Do we really want to include compiler headers? AFAICT it's not a
> built-in. Also what about clang?
>
> This thing seems trivial enough to build our own, it's a single damn
> instruction. That also means we don't have to worry about changes to
> header files we don't control.

Then, what about moving what I had earlier to vdso.h?
If we don't want __i386__ either, then make it two macros.

+.macro ENDBR
+#ifdef CONFIG_X86_CET
+#ifdef __i386__
+	endbr32
+#else
+	endbr64
+#endif
+#endif
+.endm