x86/entry/64: Validate THUNK GSBASE when CONGIG_DEBUG_ENTRY=y

The various asm THUNK helpers must only be called with kernel
GSBASE.  Just in case they don't end up accessing percpu variables,
access one in the THUNK asm (when CONFIG_DEBUG_ENTRY=y) to make
mistakes more obvious.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
1 file changed