New patch to review for coreboot: [WIP] arch/riscv: Better trap handling diagnostics

[Jonathan Neuschäfer]

Jonathan Neuschäfer ([e-mail]) just uploaded a new patch set to gerrit, which you can find at https://review.coreboot.org/16016

-gerrit

commit 9bd8814c73599b25f027b6a955dd3a330ff20148
Author: Jonathan Neuschäfer 
Date:   Mon Aug 1 19:42:27 2016 +0200

[WIP] arch/riscv: Better trap handling diagnostics

WIP: By now I should probably move the diagnistic prints into a
    function.

Change-Id: I57032f958c88ea83a420e93b459df4f620799d84
    Signed-off-by: Jonathan Neuschäfer 
---
 src/arch/riscv/trap_handler.c | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/src/arch/riscv/trap_handler.c b/src/arch/riscv/trap_handler.c
index 193be61..afb02de 100644
--- a/src/arch/riscv/trap_handler.c
+++ b/src/arch/riscv/trap_handler.c
@@ -84,11 +84,24 @@ void handle_supervisor_call(trapframe *tf) {
    asm volatile("j supervisor_call_return");
 }

+static const char *mstatus_to_previous_mode(uintptr_t ms)
+{
+	switch (ms & MSTATUS_MPP) {
+		case 0x00000000: return "user";
+		case 0x00000800: return "supervisor";
+		case 0x00001000: return "hypervisor";
+		case 0x00001800: return "machine";
+	}
+
+	return "unknown";
+}
+
 void trap_handler(trapframe *tf) {
    write_csr(mscratch, tf);
    uintptr_t cause;
    void *epc;
    void *badAddr;
+	const char *previous_mode;

// extract cause
    asm("csrr %0, mcause" : "=r"(cause));
@@ -99,6 +112,8 @@ void trap_handler(trapframe *tf) {
    // extract bad address
    asm("csrr %0, mbadaddr" : "=r"(badAddr));

+	previous_mode = mstatus_to_previous_mode(read_csr(mstatus));
+
    switch(cause) {
    	case 0:
    		printk(BIOS_DEBUG, "Trap: Instruction address misaligned\n");
@@ -107,23 +122,28 @@ void trap_handler(trapframe *tf) {
    		printk(BIOS_DEBUG, "Trap: Instruction access fault\n");
    		printk(BIOS_DEBUG, "Bad instruction pc: %p\n", epc);
    		printk(BIOS_DEBUG, "Address: %p\n", badAddr);
+			printk(BIOS_DEBUG, "Previous mode: %s\n", previous_mode);
    		break;
    	case 2:
    		printk(BIOS_DEBUG, "Trap: Illegal instruction\n");
    		printk(BIOS_DEBUG, "Bad instruction pc: %p\n", epc);
    		printk(BIOS_DEBUG, "Address: %p\n", badAddr);
+			printk(BIOS_DEBUG, "Previous mode: %s\n", previous_mode);
    		break;
    	case 3:
    		printk(BIOS_DEBUG, "Trap: Breakpoint\n");
+			printk(BIOS_DEBUG, "Bad instruction pc: %p\n", epc);
    		break;
    	case 4:
    		printk(BIOS_DEBUG, "Trap: Load address misaligned\n");
+			printk(BIOS_DEBUG, "Previous mode: %s\n", previous_mode);
    		handle_misaligned_load(tf);
    		break;
    	case 5:
    		printk(BIOS_DEBUG, "Trap: Load access fault\n");
    		printk(BIOS_DEBUG, "Bad instruction pc: %p\n", epc);
    		printk(BIOS_DEBUG, "Load Address: %p\n", badAddr);
+			printk(BIOS_DEBUG, "Previous mode: %s\n", previous_mode);
    		break;
    	case 6:
    		printk(BIOS_DEBUG, "Trap: Store address misaligned\n");
@@ -135,6 +155,7 @@ void trap_handler(trapframe *tf) {
    		printk(BIOS_DEBUG, "Trap: Store access fault\n");
    		printk(BIOS_DEBUG, "Bad instruction pc: %p\n", epc);
    		printk(BIOS_DEBUG, "Store Address: %p\n", badAddr);
+			printk(BIOS_DEBUG, "Previous mode: %s\n", previous_mode);
    		break;
    	case 8:
    		printk(BIOS_DEBUG, "Trap: Environment call from U-mode\n");