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

On Tue, Mar 16, 2021 at 01:05:30PM -0700, Yu, Yu-cheng wrote:

On 3/16/2021 12:57 PM, Peter Zijlstra wrote:

quoted

On Tue, Mar 16, 2021 at 10:12:39AM -0700, Yu, Yu-cheng wrote:

quoted

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.