libpayload: Add mock architecture

Mock architecture can be used to build libpayload using host compiler.
It can be enabled by setting ARCH_MOCK=y in the dotconfig. It sets
LITTLE_ENDIAN=y, as most machines these days use little-endian CPUs.
Libpayload will use HOSTCC as CC, HOSTLD as LD, etc. instead of tools
provided by xcompile.
Mock architecture configuration can be used by payloads for testing
purposes. Thanks to it, tests can be architecture-independent,
and can be executed without requiring compatible Kconfig options,
e.g. ARCH_ARM64=y for ARM64 machine. However, one has to provide
implementation for most architecture-specific functions present
in arch/* directories.

Signed-off-by: Jakub Czapiga <jacz@semihalf.com>
Change-Id: Ie3a6e6f6cad2f8a2e48a8e546d3b79c577653080
Reviewed-on: https://review.coreboot.org/c/coreboot/+/57708
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>

payloads/libpayload/arch/mock/Kconfig

@@ -0,0 +1,16 @@
+# SPDX-License-Identifier: GPL-2.0-only
+
+if ARCH_MOCK
+
+config ARCH_MOCK_BIG_ENDIAN
+	bool "Use big-endian for mock architecture"
+	default n
+	help
+	  This option enables big-endinan support in the code.
+
+config ARCH_SPECIFIC_OPTIONS
+	def_bool y
+	select LITTLE_ENDIAN if !ARCH_MOCK_BIG_ENDIAN
+	select BIG_ENDIAN if ARCH_MOCK_BIG_ENDIAN
+
+endif

payloads/libpayload/arch/mock/Makefile.inc

@@ -0,0 +1,7 @@
+# SPDX-License-Identifier: GPL-2.0-only
+
+head.o-y += head.c
+
+libc-y += virtual.c
+
+libcbfs-$(CONFIG_LP_CBFS) += mock_media.c

payloads/libpayload/arch/mock/head.c

@@ -0,0 +1,3 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+/* This file is empty on purpose. It should not be used. */

payloads/libpayload/arch/mock/libpayload.ldscript

@@ -0,0 +1,3 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+/* This file is empty on purpose. It is present only to satisfy install script */

payloads/libpayload/arch/mock/mock_media.c

@@ -0,0 +1,10 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#include <cbfs.h>
+
+int libpayload_init_default_cbfs_media(struct cbfs_media *media);
+
+__attribute__((weak)) int libpayload_init_default_cbfs_media(struct cbfs_media *media)
+{
+	return -1;
+}

payloads/libpayload/arch/mock/virtual.c

@@ -0,0 +1,10 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#include <unistd.h>
+
+unsigned long virtual_offset = 0;
+
+int getpagesize(void)
+{
+	return 4096;
+}