sbl b13: NOP null-struct strb; vec trap banked regs+BKPT

qemu/saimaa.c

@@ -442,6 +442,8 @@ static void saimaa_machine_init(MachineState *machine)
             cpu_physical_memory_write(0x085FFF5C, &v, 4);
             v = 0x8016183; /* S5 pop10 @ff50: 0x8013ae4 caller */
             cpu_physical_memory_write(0x085FFF74, &v, 4);
+            v = 0x8013ba5; /* S6 ldmia.w @7afc: sp=0x85fff20, pc=[+36] */
+            cpu_physical_memory_write(0x085FFF44, &v, 4);
             {   /* words that popped regs must read as 0 (not stub-fill) */
                 uint32_t z = 0;
                 cpu_physical_memory_write(0x085FFF58, &z, 4); /* r7 src */

tools/sbl_patch.py

@@ -133,6 +133,28 @@ def main():
     assert d[o:o + 4].hex() == '07f026be', hx(d, 0x8013AA8)
     d[o:o + 4] = bytes.fromhex('c046c046')
     save(d, 'img0_b12.elf')
+    # b13 = b12 + NOP strb.w fp,[r1,#-7]! at 0x8006684 (helper stores
+    # fp into struct r1, but r1 arrives NULL from 0x8007e82 chain;
+    # store to [0-7]=0xfffffff9 faults; struct unrecoverable here)
+    d = bytearray(base)
+    for va, (a, b) in BLX2BL.items():
+        set4(d, va, b)
+    for va, exp, new in [
+        (0x802F664, 'e4f77efc', 'c046c046'),
+        (0x802F672, 'e6f7bbfa', 'c046c046'),
+        (0x802F678, 'e9f7fef9', 'c046c046'),
+        (0x801B71E, '9847fee7', 'c046c046'),
+        (0x8008396, 'fef780f9', 'c046c046'),
+        (0x8016184, 'fdf790fc', 'c046c046'),
+        (0x801B76C, '280b0508', '00000708'),
+        (0x8006684, '01f807bd', '46c046c0'),
+    ]:
+        assert hx(d, va) == exp, (hex(va), hx(d, va))
+        set4(d, va, new)
+    o = off(0x8013AA8)
+    assert d[o:o + 4].hex() == '07f026be', hx(d, 0x8013AA8)
+    d[o:o + 4] = bytes.fromhex('c046c046')
+    save(d, 'img0_b13.elf')
 
 
 if __name__ == '__main__':