Add support for user-specified exception handlers

libctru/include/3ds/errf.h

@@ -110,3 +110,13 @@ Result ERRF_ThrowResult(Result failure);
  * on development units/patched ErrDisp.
  */
 Result ERRF_ThrowResultWithMessage(Result failure, const char* message);
+
+/**
+ * @brief Handles an exception using ErrDisp.
+ * @param excep Exception information
+ * @param regs CPU registers
+ *
+ * You might want to clear ENVINFO's bit0 to be able to see any debugging information.
+ * @sa threadOnException
+ */
+void ERRF_ExceptionHandler(ERRF_ExceptionInfo* excep, CpuRegisters* regs) __attribute__((noreturn));

libctru/include/3ds/thread.h

@@ -7,10 +7,23 @@
 #include <3ds/result.h>
 #include <3ds/synchronization.h>
 #include <3ds/svc.h>
+#include <3ds/errf.h>
+
+/// Makes the exception handler reuse the stack of the faulting thread as-is
+#define RUN_HANDLER_ON_FAULTING_STACK   ((void*)1)
+
+/// Makes the exception handler push the exception data on its stack
+#define WRITE_DATA_TO_HANDLER_STACK     NULL
+
+/// Makes the exception handler push the exception data on the stack of the faulting thread
+#define WRITE_DATA_TO_FAULTING_STACK    ((ERRF_ExceptionData*)1)
 
 /// libctru thread handle type
 typedef struct Thread_tag* Thread;
 
+/// Exception handler type, necessarily an ARM function that does not return.
+typedef void (*ExceptionHandler)(ERRF_ExceptionInfo* excep, CpuRegisters* regs);
+
 /**
  * @brief Creates a new libctru thread.
  * @param entrypoint The function that will be called first upon thread creation
@@ -82,3 +95,26 @@ Thread threadGetCurrent(void);
  * @param rc Exit code
  */
 void threadExit(int rc) __attribute__((noreturn));
+
+/**
+ * @brief Sets the exception handler for the current thread. Called from the main thread, this sets the default handler.
+ * @param handler The exception handler, necessarily an ARM function that does not return
+ * @param stack_top A pointer to the top of the stack that will be used by the handler. See also @ref RUN_HANDLER_ON_FAULTING_STACK
+ * @param exception_data A pointer to the buffer that will contain the exception data.
+                         See also @ref WRITE_DATA_TO_HANDLER_STACK and @ref WRITE_DATA_TO_FAULTING_STACK
+ *
+ * To have CPU exceptions reported through this mechanism, it is normally necessary that UNITINFO is set to a non-zero value when Kernel11 starts,
+ * and this mechanism is also controlled by @ref svcKernelSetState type 6, see 3dbrew.
+ * 
+ * VFP exceptions are always reported this way even if the process is being debugged using the debug SVCs.
+ *
+ * The current thread need not be a libctru thread.
+ */
+static inline void threadOnException(ExceptionHandler handler, void* stack_top, ERRF_ExceptionData* exception_data)
+{
+	u8* tls = (u8*)getThreadLocalStorage();
+
+	*(u32*)(tls + 0x40) = (u32)handler;
+	*(u32*)(tls + 0x44) = (u32)stack_top;
+	*(u32*)(tls + 0x48) = (u32)exception_data;
+}

libctru/source/errf.c

@@ -106,3 +106,30 @@ Result ERRF_ThrowResultWithMessage(Result failure, const char* message)
 
 	return ret;
 }
+
+void ERRF_ExceptionHandler(ERRF_ExceptionInfo* excep, CpuRegisters* regs)
+{
+	ERRF_FatalErrInfo error;
+	Result ret;
+
+	if (R_FAILED(ret = errfInit()))
+	{
+		svcBreak(USERBREAK_PANIC);
+		for(;;);
+	}
+
+	memset(&error, 0, sizeof(error));
+
+	error.type = ERRF_ERRTYPE_EXCEPTION;
+
+	error.pcAddr = regs->pc;
+	getCommonErrorData(&error, 0);
+	error.data.exception_data.excep = *excep;
+	error.data.exception_data.regs = *regs;	
+
+	ret = ERRF_Throw(&error);
+
+	errfExit();
+
+	for(;;);
+}