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-rw-r--r--Debugger/undef_handler.S3
1 files changed, 2 insertions, 1 deletions
diff --git a/Debugger/undef_handler.S b/Debugger/undef_handler.S
index 61b8a5d..34154f7 100644
--- a/Debugger/undef_handler.S
+++ b/Debugger/undef_handler.S
@@ -35,7 +35,8 @@ undef_handler:
On entry, LR_undef points to one instruction past the UNDEF instruction
*/
ldr sp, =__debugger_stack__
- stmfd sp, {r0-r15}^ /* Save workspace, user mode's pc via 'S' flag */
+ stmfd sp, {r0-r15}^ /* Save workspace, user mode's pc via 'S' flag, R15: placeholder */
+ str lr, [sp, #-4] /* Keep User's Next Instr Pointer (in UNDEF SP) in user mode R15 */
sub sp, sp, #(4*16) /* Need to manually update SP(undef) */
mrs r1, spsr /* Copy SPSR to r0 */
tst r1, #CPSR_THUMB /* Check for Thumb Mode */