Disable IRQ/FIQ while in svcBackdoor

diff --git a/external/bits/backdoor.s b/external/bits/backdoor.s
index 9a22f67d215a06177fe1a072de697439ffec13d5..17c2f23525722b21ecb95952cb211dce7a09abc6 100644 (file)
--- a/external/bits/backdoor.s
+++ b/external/bits/backdoor.s
@@ -1,16 +1,36 @@
-// This is svcBackdoor's code from earlier FIRMs
-// Luckily, no ARM9/ARM11 specific instructions are used here.
-// It can just be assembled via ARM9 gas.
+// This is a "backdoor" supervisor call we install.
+// Roughly, this is based on nintendo's, but there are a few defecits in their code.
+
+// Namely, Nintendo's will crash ARM11 kernel if an IRQ/FIQ is hit while in the call,
+// so we play it safe and disable them in cpsr while in backdoor.
+
 .section .text
 .global _start
 _start:
+       // Disable FIQ and IRQ.
+       mrs r1, cpsr
+       orr r1, #0xc0
+       msr cpsr_c, r1
+
+       // Save
        bic r1, sp, #0xff
        orr r1, r1, #0xf00
        add r1, r1, #0x28
        ldr r2, [r1]
        stmdb r2!, {sp, lr}
        mov sp, r2
+
+       // Call user function.
        blx r0
+
+       // Renable FIQ and IRQ.
+       mrs r1, cpsr
+       bic r1, #0xc0
+       msr cpsr_c, r1
+
+       // Restore registers.
        pop {r0, r1}
        mov sp, r0
+
+       // Return.
        bx r1