Implement custom abort and fault handler for debugging

src/runtime/runtime_cortexm_hardfault.go

@@ -0,0 +1,39 @@
+// +build cortexm,!nxp
+
+package runtime
+
+import (
+	"unsafe"
+)
+
+// This function is called at HardFault.
+// Before this function is called, the stack pointer is reset to the initial
+// stack pointer (loaded from addres 0x0) and the previous stack pointer is
+// passed as an argument to this function. This allows for easy inspection of
+// the stack the moment a HardFault occurs, but it means that the stack will be
+// corrupted by this function and thus this handler must not attempt to recover.
+//
+// For details, see:
+// https://community.arm.com/developer/ip-products/system/f/embedded-forum/3257/debugging-a-cortex-m0-hard-fault
+// https://blog.feabhas.com/2013/02/developing-a-generic-hard-fault-handler-for-arm-cortex-m3cortex-m4/
+//export handleHardFault
+func handleHardFault(sp *interruptStack) {
+	print("fatal error: ")
+	if uintptr(unsafe.Pointer(sp)) < 0x20000000 {
+		print("stack overflow")
+	} else {
+		// TODO: try to find the cause of the hard fault. Especially on
+		// Cortex-M3 and higher it is possible to find more detailed information
+		// in special status registers.
+		print("HardFault")
+	}
+	print(" with sp=", sp)
+	if uintptr(unsafe.Pointer(&sp.PC)) >= 0x20000000 {
+		// Only print the PC if it points into memory.
+		// It may not point into memory during a stack overflow, so check that
+		// first before accessing the stack.
+		print(" pc=", sp.PC)
+	}
+	println()
+	abort()
+}