Add option to use Ada code in ramstage

If selected, libgnat will be linked into ramstage. And, to support Ada
package intializations, we have to call ramstage_adainit().

Change-Id: I11417db21f16bf3007739a097d63fd592344bce3
Signed-off-by: Nico Huber <nico.huber@secunet.com>
Reviewed-on: https://review.coreboot.org/16944
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/Kconfig

@@ -1243,3 +1243,8 @@ config CHECKLIST_DATA_FILE_LOCATION
 	  symbols contained only in <stage>_complete.dat will be flagged as
 	  required and not implemented if a weak implementation is found in the
 	  resulting image.
+
+config RAMSTAGE_ADA
+	def_bool n
+	help
+	  Selected by features that use Ada code in ramstage.

src/include/adainit.h

@@ -0,0 +1,35 @@
+/*
+ * This file is part of the coreboot project.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; version 2 of the License.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#ifndef _ADAINIT_H
+#define _ADAINIT_H
+
+/**
+ * @file adainit.h
+ *
+ * Ada supports some complex constructs that result in code for runtime
+ * initialization. It's also possible to have explicit procedures for
+ * package level initialization (e.g. you can initialize huge arrays in
+ * a loop instead of cluttering the binary).
+ *
+ * When an Ada main() is in charge, GNAT emmits the call to the initia-
+ * lizations automatically. When not, we have to call it explicitly.
+ */
+
+#if IS_ENABLED(CONFIG_RAMSTAGE_ADA)
+void ramstage_adainit(void);
+#else
+static inline void ramstage_adainit(void) {}
+#endif
+
+#endif /* _ADAINIT_H */

src/lib/gnat/Makefile.inc

@@ -60,3 +60,7 @@ $(foreach arch,$(standard-archs), \
 
 $(foreach arch,$(standard-archs), \
 	$(eval $(call libgnat-template,$(arch))))
+
+ifeq ($(CONFIG_RAMSTAGE_ADA),y)
+ramstage-libs += $$(obj)/libgnat-$(ARCH-ramstage-y)/libgnat.a
+endif

src/lib/hardwaremain.c

@@ -18,6 +18,7 @@
  * C Bootstrap code for the coreboot
  */
 
+#include <adainit.h>
 #include <arch/exception.h>
 #include <bootstate.h>
 #include <console/console.h>
@@ -429,6 +430,18 @@ static void boot_state_schedule_static_entries(void)
 
 void main(void)
 {
+	/*
+	 * We can generally jump between C and Ada code back and forth
+	 * without trouble. But since we don't have an Ada main() we
+	 * have to do some Ada package initializations that GNAT would
+	 * do there. This has to be done before calling any Ada code.
+	 *
+	 * The package initializations should not have any dependen-
+	 * cies on C code. So we can call them here early, and don't
+	 * have to worry at which point we can start to use Ada.
+	 */
+	ramstage_adainit();
+
 	/* TODO: Understand why this is here and move to arch/platform code. */
 	/* For MMIO UART this needs to be called before any other printk. */
 	if (IS_ENABLED(CONFIG_ARCH_X86))