libpayload/arch/x86: Update API handling of CBTABLE handoff

The payload API of coreboot described in
https://www.coreboot.org/Payload_API does not reflect the current
handoff mechanism to hand the coreboot tables off. Therefore the
arguments supplied by coreboot (cbtable) will currently never be parsed
correctly and libpayload has to search for the coreboot tables by
iterating through memory.

This patch removes the old payload API implementation and just takes the
coreboot table pointer from the first argument on the stack.

Tested: started prodrive/atlas with coreinfo payload

Signed-off-by: Maximilian Brune <maximilian.brune@9elements.com>
Change-Id: I51fb0cfc81043cbfe3fc9c8ea0776add2d6a42b2
Reviewed-on: https://review.coreboot.org/c/coreboot/+/74965
Reviewed-by: Julius Werner <jwerner@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

payloads/libpayload/arch/x86/head.S

@@ -55,11 +55,6 @@ mb_header:
 	.long _end
 	.long _init
 
-#define CB_MAGIC_VALUE	0x12345678
-#define CB_MAGIC	0x04
-#define CB_ARGV		0x08
-#define CB_ARGC		0x10
-
 /*
  * This function saves off the previous stack and switches us to our
  * own execution environment.
@@ -72,18 +67,10 @@ _init:
 	movl %eax, loader_eax
 	movl %ebx, loader_ebx
 
-	/* Copy argv[] and argc as demanded by the Payload API,
-	 * see https://www.coreboot.org/Payload_API and exec.S.
-	 */
-	cmpl $CB_MAGIC_VALUE, CB_MAGIC(%esp)
-	jne 1f
+	/* save pointer to coreboot tables */
+	movl 4(%esp), %eax
+	movl %eax, cb_header_ptr
 
-	movl CB_ARGV(%esp), %eax
-	movl %eax, main_argv
-
-	movl CB_ARGC(%esp), %eax
-	movl %eax, main_argc
-1:
 	/* Store current stack pointer and set up new stack. */
 	movl %esp, %eax
 	movl $_stack, %esp