Merge patch series "riscv: Dump faulting instructions in oops handler"

Björn Töpel <bjorn@kernel.org> says:

From: Björn Töpel <bjorn@rivosinc.com>

RISC-V does not dump faulting instructions in the oops handler. This
series adds "Code:" dumps to the oops output together with
scripts/decodecode support.

* b4-shazam-merge:
  scripts/decodecode: Add support for RISC-V
  riscv: Add instruction dump to RISC-V splats

Link: https://lore.kernel.org/r/20230119074738.708301-1-bjorn@kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

Author: palmer-dabbelt

arch/riscv/kernel/traps.c

@@ -29,6 +29,27 @@ int show_unhandled_signals = 1;
 
 static DEFINE_SPINLOCK(die_lock);
 
+static void dump_kernel_instr(const char *loglvl, struct pt_regs *regs)
+{
+	char str[sizeof("0000 ") * 12 + 2 + 1], *p = str;
+	const u16 *insns = (u16 *)instruction_pointer(regs);
+	long bad;
+	u16 val;
+	int i;
+
+	for (i = -10; i < 2; i++) {
+		bad = get_kernel_nofault(val, &insns[i]);
+		if (!bad) {
+			p += sprintf(p, i == 0 ? "(%04hx) " : "%04hx ", val);
+		} else {
+			printk("%sCode: Unable to access instruction at 0x%px.\n",
+			       loglvl, &insns[i]);
+			return;
+		}
+	}
+	printk("%sCode: %s\n", loglvl, str);
+}
+
 void die(struct pt_regs *regs, const char *str)
 {
 	static int die_counter;
@@ -44,8 +65,10 @@ void die(struct pt_regs *regs, const char *str)
 
 	pr_emerg("%s [#%d]\n", str, ++die_counter);
 	print_modules();
-	if (regs)
+	if (regs) {
 		show_regs(regs);
+		dump_kernel_instr(KERN_EMERG, regs);
+	}
 
 	cause = regs ? regs->cause : -1;
 	ret = notify_die(DIE_OOPS, str, regs, 0, cause, SIGSEGV);

scripts/decodecode

@@ -93,6 +93,11 @@ disas() {
 		${CROSS_COMPILE}strip $t.o
 	fi
 
+	if [ "$ARCH" = "riscv" ]; then
+		OBJDUMPFLAGS="-M no-aliases --section=.text -D"
+		${CROSS_COMPILE}strip $t.o
+	fi
+
 	if [ $pc_sub -ne 0 ]; then
 		if [ $PC ]; then
 			adj_vma=$(( $PC - $pc_sub ))
@@ -126,8 +131,13 @@ get_substr_opcode_bytes_num()
 	do
 		substr+="$opc"
 
+		opcode="$substr"
+		if [ "$ARCH" = "riscv" ]; then
+			opcode=$(echo $opcode | tr ' ' '\n' | tac | tr -d '\n')
+		fi
+
 		# return if opcode bytes do not match @opline anymore
-		if ! echo $opline | grep -q "$substr";
+		if ! echo $opline | grep -q "$opcode";
 		then
 			break
 		fi