On 2/5/20 10:19 AM, Yu-cheng Yu wrote:

+# Check assembler Shadow Stack suppot

				  ^ support

+ifdef CONFIG_X86_INTEL_SHADOW_STACK_USER
+  ifeq ($(call as-instr, saveprevssp, y),)
+      $(error CONFIG_X86_INTEL_SHADOW_STACK_USER not supported by the assembler)
+  endif
+endif

Is this *just* looking for instruction support in the assembler?

We usually just .byte them, like this for pkeys:

        asm volatile(".byte 0x0f,0x01,0xee\n\t"
                     : "=a" (pkru), "=d" (edx)
                     : "c" (ecx));

That way everybody with old toolchains can still build the kernel (and
run/test code with your config option on, btw...).