smm: Push a null stack base pointer

When generating a backtrace we need an indicator when we have hit the
beginning of the stack. The i386 ABI states that %ebp points to the next
stack frame. NULL can be used to indicate the end of the stack.

We could add a NULL return pointer at %ebp+4, but I decided to omit it
since a NULL stack pointer can be used as an indicator that there is no
return pointer.

BUG=b:80539294
TEST=built and tested on grunt

Change-Id: I8a48114d31a5c716335d264fa4fe4da41dc5bf11
Signed-off-by: Raul E Rangel <rrangel@chromium.org>
Reviewed-on: https://review.coreboot.org/27226
Reviewed-by: Martin Roth <martinroth@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
1 file changed