leon: In sparcisr, get location to install TA 3 handler from TBR.

The base location of TBR may be different from 0x40000000.

leon-common/sparcisr.c

@@ -6,13 +6,25 @@
 #include <stdint.h>
 #include "leon-common/sparcisr.h"
 
+// This function retrieves the value of the Trap Base Register, to be used
+// to install a window flushing trap handler next.
+static void TRAP_read_TBR(volatile uint32_t* const tbrPtr) {
+    asm("mov %0, %%o1" : : "r" (tbrPtr) : "%o1");
+    asm("rd %%tbr, %%o0" : : : "%o0");
+    asm("st %o0, [%o1]");
+}
+
 // This function installs the "ta 3" ISR which handles window flushing.
 // It is only needed for Edisoft RTEMS 4.8 because the trap handler is not
 // included in that version, but it is needed by MicroPython to implement
 // setjmp/longjmp calls for exception handling.
 void sparc_install_ta_3_window_flush_isr(void) {
     extern int sparc_window_flush_trap_handler(void);
-    uint32_t *m = (uint32_t*)0x40000830;
+    volatile uint32_t tbr = 0;
+    TRAP_read_TBR(&tbr);
+    tbr &= 0xfffff000;
+    tbr |= 0x830;
+    uint32_t *m = (uint32_t*)tbr;
     uint32_t addr = (uint32_t)sparc_window_flush_trap_handler;
     m[0] = 0xa1480000; // rd %psr, %l0
     m[1] = 0x29100000 | (addr >> 10); // sethi %hi(addr), %l4