Cortex-M3 vector_catch testing support

The "cm3-ftest.cfg" can be used to verify that OpenOCD handles
certain faults correctly:

 - Test #1: it ignores faults that it wasn't told to catch
 - Test #2: if vector_catch is told to catch, it catches

The "fault.c" generates ASM code to trigger faults, while the
config script loads and runs pre-compiled code.

This covers most, but not all, of the vector_catch options.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>

testing/examples/cortex/fault.c

@@ -0,0 +1,152 @@
+/*
+ * COMPILE:  arm-none-eabi-gcc -mthumb -march=armv7-m ...
+ *	... plus, provide at least a default exception vector table.
+ *
+ * RUN:  this is best run from SRAM.  It starts at main() then triggers
+ * a fault before more than a handful of instructions have executed.
+ * Run each test case in two modes:
+ *
+ * (1)	Faults caught on the Cortex-M3.  Default handlers are usually
+ *	loop-to-self NOPs, so a debugger won't notice faults until they
+ *	halt the core and examine xSPR and other registers.
+ *
+ *	To verify the fault triggered, issue "halt" from OpenOCD; you
+ *	should be told about the fault and (some of) its details.
+ *	Then it's time to run the next test.
+ *
+ *	NOTE however that "reset" will restart everything; verify that
+ *	case by observing your reset handler doing its normal work.
+ *
+ * (2)	Faults intercepted by OpenOCD "vector_catch ..." commands.
+ *
+ *	OpenOCD should tell you about the fault, and show the same
+ *	details, without your "halt" command.
+ *
+ * Someday, a fancy version of this code could provide a vector table and
+ * fault handlers which use semihosting (when that works on Cortex-M3) to
+ * report what happened, again without needing a "halt" command.
+ */
+
+
+/* These symbols match the OpenOCD "cortex_m3 vector_catch" bit names. */
+enum vc_case {
+	hard_err,
+	int_err,
+	bus_err,
+	state_err,
+	chk_err,
+	nocp_err,
+	mm_err,
+	reset,
+};
+
+/* REVISIT come up with a way to avoid recompiling, maybe:
+ *  - write it in RAM before starting
+ *  - compiled-in BKPT, manual patch of r0, then resume
+ *  - ...
+ */
+
+#ifndef VC_ID
+#warning "no VC_ID ... using reset"
+#define VC_ID reset
+#endif
+
+int main(void) __attribute__ ((externally_visible, noreturn));
+
+/*
+ * Trigger various Cortex-M3 faults to verify that OpenOCD behaves OK
+ * in terms of its vector_catch handling.
+ *
+ * Fault handling should be left entirely up to the application code
+ * UNLESS a "vector_catch" command tells OpenOCD to intercept a fault.
+ *
+ * See ARMv7-M architecure spec table B1-9 for the list of faults and
+ * their mappings to the vector catch bits.
+ */
+int main(void)
+{
+	/* One test case for each vector catch bit.  We're not doing
+	 * hardware testing; so it doesn't matter when some DEMCR bits
+	 * could apply in multiple ways.
+	 */
+	switch (VC_ID) {
+
+	/* "cortex_m3 vector_catch hard_err" */
+	case hard_err:
+		/* FORCED - Fault escalation */
+
+		/* FIXME code this */
+		break;
+
+	/* "cortex_m3 vector_catch int_err" */
+	case int_err:
+		/* STKERR -- Exception stack BusFault */
+
+		/* FIXME code this */
+		break;
+
+	/* "cortex_m3 vector_catch bus_err" */
+	case bus_err:
+		/* PRECISERR -- precise data bus read
+		 * Here we assume a Cortex-M3 with 512 MBytes SRAM is very
+		 * unlikely, so the last SRAM byte isn't a valid address.
+		 */
+		__asm__ volatile(
+			"mov r0, #0x3fffffff\n"
+			"ldrb r0, [r0]\n"
+			);
+		break;
+
+	/* "cortex_m3 vector_catch state_err" */
+	case state_err:
+		/* UNDEFINSTR -- architectural undefined instruction */
+		__asm__ volatile(".hword 0xde00");
+		break;
+
+	/* "cortex_m3 vector_catch chk_err" */
+	case chk_err:
+		/* UNALIGNED ldm */
+		__asm__ volatile(
+			"mov r0, #1\n"
+			"ldm r0, {r1, r2}\n"
+			);
+		break;
+
+	/* "cortex_m3 vector_catch nocp_err" */
+	case nocp_err:
+		/* NOCP ... Cortex-M3 has no coprocessors (like CP14 DCC),
+		 * but these instructions are allowed by ARMv7-M.
+		 */
+		__asm__ volatile("mrc p14, 0, r0, c0, c5, 0");
+		break;
+
+	/* "cortex_m3 vector_catch mm_err" */
+	case mm_err:
+		/* IACCVIOL -- instruction fetch from an XN region */
+		__asm__ volatile(
+			"mov r0, #0xe0000000\n"
+			"mov pc, r0\n"
+			);
+		break;
+
+	/* "cortex_m3 vector_catch reset" */
+	case reset:
+		__asm__ volatile(
+			/* r1 = SYSRESETREQ */
+			"mov r1, #0x0004\n"
+			/* r1 |= VECTKEY */
+			"movt r1, #0x05fa\n"
+			/* r0 = &AIRCR */
+			"mov r0, #0xed00\n"
+			"add r0, #0xc\n"
+			"movt r0, #0xe000\n"
+			/* AIRCR = ... */
+			"str r1, [r0, #0]\n"
+			);
+		break;
+	}
+
+	/* don't return */
+	while (1)
+		continue;
+}