ramstage: prepare for relocation

The current ramstage code contains uses of symbols that cause issues
when the ramstage is relocatable. There are 2 scenarios resolved by this
patch:

1. Absolute symbols that are actually sizes/limits. The symbols are
   problematic when relocating a program because there is no way to
   distinguish a symbol that shouldn't be relocated and one that can.
   The only way to handle these symbols is to write a program to post
   process the relocations and keep a whitelist of ones that shouldn't
   be relocated. I don't believe that is a route that should be taken
   so fix the users of these sizes/limits encoded as absolute symbols
   to calculate the size at runtime or dereference a variable in memory
   containing the size/limit.

2. Absoulte symbols that were relocated to a fixed address. These
   absolute symbols are generated by assembly files to be placed at a
   fixed location. Again, these symbols are problematic because one
   can't distinguish a symbol that can't be relocated. The symbols
   are again resolved at runtime to allow for proper relocation.

For the symbols defining a size either use 2 symbols and calculate the
difference or provide a variable in memory containing the size.

Change-Id: I1ef2bfe6fd531308218bcaac5dcccabf8edf932c
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/2789
Tested-by: build bot (Jenkins)
Reviewed-by: Marc Jones <marc.jones@se-eng.com>

3 files changed, 25 insertions, 5 deletions

diff --git a/src/cpu/intel/haswell/mp_init.c b/src/cpu/intel/haswell/mp_init.c
index 3076d070ec..47683fb78c 100644
--- a/src/cpu/intel/haswell/mp_init.c
+++ b/src/cpu/intel/haswell/mp_init.c
@@ -66,7 +66,7 @@ struct saved_msr {
 extern char _binary_sipi_vector_start[];
 /* These symbols are defined in c_start.S. */
 extern char gdt[];
-extern char gdt_limit[];
+extern char gdt_end[];
 extern char idtarg[];
 
 /* This table keeps track of each CPU's APIC id. */
@@ -189,7 +189,7 @@ static void setup_default_sipi_vector_params(struct sipi_params *sp)
 	int i;
 
 	sp->gdt = (u32)&gdt;
-	sp->gdtlimit = (u32)&gdt_limit;
+	sp->gdtlimit = (u32)&gdt_end - (u32)&gdt - 1;
 	sp->idt_ptr = (u32)&idtarg;
 	sp->stack_size = CONFIG_STACK_SIZE;
 	sp->stack_top = (u32)&_estack;
diff --git a/src/cpu/x86/lapic/lapic_cpu_init.c b/src/cpu/x86/lapic/lapic_cpu_init.c
index 9a00b8289f..69430d551f 100644
--- a/src/cpu/x86/lapic/lapic_cpu_init.c
+++ b/src/cpu/x86/lapic/lapic_cpu_init.c
@@ -52,12 +52,30 @@ int  lowmem_backup_size;
 #endif
 
 extern char _secondary_start[];
+extern char _secondary_gdt_addr[];
+extern char gdt[];
+extern char gdt_end[];
+
+static inline void setup_secondary_gdt(void)
+{
+	u16 *gdt_limit;
+	u32 *gdt_base;
+
+	gdt_limit = (void *)&_secondary_gdt_addr;
+	gdt_base = (void *)&gdt_limit[1];
+
+	*gdt_limit = (u32)&gdt_end - (u32)&gdt - 1;
+	*gdt_base = (u32)&gdt;
+}
 
 static void copy_secondary_start_to_lowest_1M(void)
 {
 	extern char _secondary_start_end[];
 	unsigned long code_size;
 
+	/* Fill in secondary_start's local gdt. */
+	setup_secondary_gdt();
+
 	code_size = (unsigned long)_secondary_start_end - (unsigned long)_secondary_start;
 
 #if CONFIG_HAVE_ACPI_RESUME
diff --git a/src/cpu/x86/lapic/secondary.S b/src/cpu/x86/lapic/secondary.S
index 2e0620e2da..6edcd0a366 100644
--- a/src/cpu/x86/lapic/secondary.S
+++ b/src/cpu/x86/lapic/secondary.S
@@ -3,7 +3,7 @@
 
 #if CONFIG_SMP && CONFIG_MAX_CPUS > 1
 	.text
-	.globl _secondary_start, _secondary_start_end
+	.globl _secondary_start, _secondary_start_end, _secondary_gdt_addr
 	.balign 4096
 _secondary_start:
 	.code16
@@ -28,9 +28,11 @@ _secondary_start:
 
 	ljmpl	$0x10, $__ap_protected_start
 
+	/* This will get filled in by C code. */
+_secondary_gdt_addr:
 gdtaddr:
-	.word   gdt_limit	/* the table limit */
-	.long   gdt             /* we know the offset */
+	.word   0	/* the table limit */
+	.long   0	/* we know the offset */
 
 _secondary_start_end: