On 3/16/21 10:12 AM, Yu, Yu-cheng wrote:

On 3/16/2021 8:49 AM, Dave Hansen wrote:

...

quoted

Is "#ifdef __i386__" the right thing to use here?  I guess ENDBR only
ends up getting used in the VDSO, but there's a lot of
non-userspace-exposed stuff in calling.h.  It seems a bit weird to have
the normally userspace-only __i386__ in there.

I don't see any existing direct use of __i386__ in arch/x86/entry/vdso.

Good point.  My thought was, __i386__ comes from the compiler having the
-m32 command-line option, and it is not dependent on anything else.

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.

First of all, I think putting the macro in calling.h is wrong if it will
be used exclusively in the VDSO.  If it's VDSO-only, please put it in a
local header in the vdso/ directory, maybe even a new cet.h.

Also, Boris asked for two *different* macros for 32 and 64-bit:

https://lore.kernel.org/linux-api/20210310231731.GK23521@zn.tnic/ (local)

Could you do that in the next version, please?