[arch][microblaze] change linker script to support having a different LMA for the vector table

The qemu target has 128KB of ram at 0 and the rest at 0x90000000.
Split the binary so that the vector table lives at 0 and everything else in
the high address.

arch/microblaze/linker.ld

@@ -8,10 +8,14 @@ SECTIONS
 
     _start = .;
 
+    /* vector table goes at 0, for qemu target, at least */
+    .vectors : AT(0) {
+        KEEP(*(.vectors))
+    }
+
     /* text/read-only data */
     /* set the load address to physical MEMBASE */
-    .text : AT(%MEMBASE% + %KERNEL_LOAD_OFFSET%) {
-        KEEP(*(.vectors))
+    .text : AT(%MEMBASE% + %KERNEL_LOAD_OFFSET% + SIZEOF(.vectors)) {
         KEEP(*(.text.boot))
         *(.text* .gnu.linkonce.t.*)
     }

arch/microblaze/rules.mk

@@ -34,7 +34,7 @@ ARCH_OPTFLAGS := -O2
 
 GLOBAL_LDFLAGS += -relax
 
-KERNEL_BASE ?= 0
+KERNEL_BASE ?= $(MEMBASE)
 KERNEL_LOAD_OFFSET ?= 0
 
 # potentially generated files that should be cleaned out with clean make rule

arch/microblaze/start.S

@@ -22,26 +22,26 @@
  */
 #include <asm.h>
 
-.section ".vectors"
-.globl _start
-_start:
+.section ".vectors", "ax"
+.globl _vectab
+_vectab:
 /* vector table here */
     # start vector
-    bri start
+    brai start
     # user exception
-    bri unhandled_exception
+    brai unhandled_exception
     # interrupt
-    bri microblaze_irq
+    brai microblaze_irq
     # break
-    bri unhandled_exception
+    brai unhandled_exception
     # hardware exception
-    bri unhandled_exception
+    brai unhandled_exception
 
     # reserved for future
 .fill (0x50 - 0x28)
 
 .section ".text.boot"
-start:
+FUNCTION(start)
     # set the default stack
     addik   r1, r0, default_stack_top
 
@@ -49,13 +49,15 @@ start:
     addik   r2, r0, _SDATA2_START__
     addik   r13, r0, _SDATA_START__
 
-    # TODO: make sure irqs are disabled and any other cpu specific setup
+    # set the processor mode to default
+    mts     rmsr, r0
 
     # zero out bss sections
     addik   r5, r0, __bss_start
     addik   r6, r0, 0
-    brlid   r15, memset
     rsubik  r7, r5, __bss_end
+    brlid   r15, memset
+    nop
 
     # arguments to main
     addik   r5, r0, 1
@@ -67,7 +69,7 @@ start:
     # shouldn't be here
     bri     .
 
-unhandled_exception:
+FUNCTION(unhandled_exception)
     bri     .
 
 .bss

platform/microblaze/rules.mk

@@ -11,8 +11,8 @@ MODULE_SRCS += \
 	$(LOCAL_DIR)/platform.c \
 	$(LOCAL_DIR)/uartlite.c
 
-MEMBASE := 0x0
-MEMSIZE := 0x08000000	# 128MB
+MEMBASE ?= 0x0
+MEMSIZE ?= 0x20000	# 128KB
 
 MODULE_DEPS += \
 

target/qemu-microblaze/rules.mk

@@ -5,5 +5,8 @@ GLOBAL_INCLUDES += \
 
 PLATFORM := microblaze
 
+MEMBASE ?= 0x90000000
+MEMSIZE ?= 0x08000000
+
 #include make/module.mk