[coreboot] [PATCH] v3: determine global variable location

[Carl-Daniel Hailfinger]

We need a way to find out where our stack and our global variables are
at any given moment. This is a first generic try, but doing this in a
processor-specific way would be more appropriate.

Please note that this needs a new #define or Kconfig variable somewhere:
CONFIG_RAM_STACK_LOCATION. As an alternative, we could declare the top
of memory as optimal stack location.

Signed-off-by: Carl-Daniel Hailfinger <c-d.hailfinger.devel.2006 at gmx.net>

Index: corebootv3-globalvariablelocation/arch/x86/stage1.c
===================================================================
--- corebootv3-globalvariablelocation/arch/x86/stage1.c	(Revision 925)
+++ corebootv3-globalvariablelocation/arch/x86/stage1.c	(Arbeitskopie)
@@ -70,11 +70,22 @@
 /*
  * The name is slightly misleading because this is the initial stack pointer,
  * not the address of the first element on the stack.
+ * NOTE: This function is very processor specific.
  */
 void *bottom_of_stack(void)
 {
-	/* -4 because CONFIG_CARBASE + CONFIG_CARSIZE - 4 is initial %esp */
-	return (void *)(CONFIG_CARBASE + CONFIG_CARSIZE - 4);
+	u32 onstack = (u32)&onstack;
+
+	/* Check whether the variable onstack is inside the CAR area.
+	 * If it is, assume we're still in CAR or the stack has not moved.
+	 * Otherwise return initial %esp for the RAM-based stack location.
+	 */
+	if ((onstack >= CONFIG_CARBASE) &&
+	    (onstack < CONFIG_CARBASE + CONFIG_CARSIZE - 4))
+		/* CONFIG_CARBASE + CONFIG_CARSIZE - 4 is initial %esp */
+		return (void *)(CONFIG_CARBASE + CONFIG_CARSIZE - 4);
+	/* OK, so current %esp is not inside the CAR area. */
+	return (void *) CONFIG_RAM_STACK_LOCATION;
 }
 
 struct global_vars *global_vars(void)


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