Merge #168

168: On HardFault entry use MSP/PSP depending on stack mode r=thejpster a=bytex64

Noticed this when making my own hardfault handler - none of the registers were correct. The `&ExceptionFrame` argument was wrong because I was using the PSP in Thread mode, but the handler only loads MSP. This PR inspects the EXC_RETURN value in LR and loads either MSP or PSP depending on the stack used (see section B1.5.8 in the ARMv7-M architecture manual for details on the format of EXC_RETURN).

I haven't tested this on armv6m or armv8m, but I believe it works the same across the board. Also didn't update the libraries in `bin/` since I wasn't sure if that was expected or not.

Co-authored-by: Chip <[email protected]>

Author: bors[bot]

cortex-m-rt/asm.s

@@ -6,5 +6,14 @@
   .type HardFaultTrampoline,%function
   .thumb_func
 HardFaultTrampoline:
+  # depending on the stack mode in EXC_RETURN, fetch stack pointer from
+  # PSP or MSP
+  mov r0, lr
+  mov r1, #4
+  tst r0, r1
+  bne 0f
   mrs r0, MSP
   b HardFault
+0:
+  mrs r0, PSP
+  b HardFault