x86/cpu.c: unhandled page fault: print pre-fault stack

Do basic manual unwinding and print raw stack addresses, with a
suggested invocation of addr2line to pretty-print the result.

arch/arm64/kernel/cpu.c

@@ -1205,6 +1205,10 @@ void ihk_mc_delay_us(int us)
 	arch_delay(us);
 }
 
+void arch_print_stack()
+{
+}
+
 void arch_show_interrupt_context(const void *reg)
 {
 	const struct pt_regs *regs = (struct pt_regs *)reg;

arch/x86/kernel/cpu.c

@@ -1490,6 +1490,69 @@ void arch_show_extended_context(void)
 	}
 }
 
+struct stack {
+	struct stack *rbp;
+	unsigned long eip;
+};
+
+/* KPRINTF_LOCAL_BUF_LEN is 1024, useless to go further */
+#define STACK_BUF_LEN (1024-sizeof("[  0]: "))
+static void __print_stack(struct stack *rbp, unsigned long first) {
+	char buf[STACK_BUF_LEN];
+	size_t len;
+
+	/* Build string in buffer to output a single line */
+	len = snprintf(buf, STACK_BUF_LEN,
+		       "addr2line -e smp-x86/kernel/mckernel.img -fpia");
+
+	if (first)
+		len += snprintf(buf + len, STACK_BUF_LEN - len,
+				" %#16lx", first);
+
+	while ((unsigned long)rbp > 0xffff880000000000 &&
+			STACK_BUF_LEN - len > sizeof(" 0x0123456789abcdef")) {
+		len += snprintf(buf + len, STACK_BUF_LEN - len,
+				" %#16lx", rbp->eip);
+		rbp = rbp->rbp;
+	}
+	__kprintf("%s\n", buf);
+}
+
+void arch_print_pre_interrupt_stack(const struct x86_basic_regs *regs) {
+	struct stack *rbp;
+
+	/* only for kernel stack */
+	if (regs->error & PF_USER)
+		return;
+
+	__kprintf("Pre-interrupt stack trace:\n");
+
+	/* interrupt stack heuristics:
+	 * - the first entry looks like it is always garbage, so skip.
+	 * (that is done by taking regs->rsp instead of &regs->rsp)
+	 * - that still looks sometimes wrong. For now, if it is not
+	 * within 64k of itself, look for the next entry that matches.
+	 */
+
+	rbp = (struct stack*)regs->rsp;
+
+	while ((uintptr_t)rbp > (uintptr_t)rbp->rbp
+			|| (uintptr_t)rbp + 0x10000 < (uintptr_t)rbp->rbp)
+		rbp = (struct stack *)(((uintptr_t *)rbp) + 1);
+
+	__print_stack(rbp, regs->rip);
+}
+
+void arch_print_stack() {
+	struct stack *rbp;
+
+	__kprintf("Approximative stack trace:\n");
+
+	asm("mov %%rbp, %0" : "=r"(rbp) );
+
+	__print_stack(rbp, 0);
+}
+
 /*@
   @ requires \valid(reg);
   @ assigns \nothing;
@@ -1521,6 +1584,8 @@ void arch_show_interrupt_context(const void *reg)
 
 	arch_show_extended_context();
 
+	arch_print_pre_interrupt_stack(regs);
+
 	kprintf_unlock(irqflags);
 }
 

lib/abort.c

@@ -5,6 +5,7 @@
 
 extern struct cpu_local_var *clv;
 extern void eventfd(int type);
+extern void arch_print_stack();
 
 void panic(const char *msg)
 {
@@ -16,7 +17,9 @@ void panic(const char *msg)
 	}
 	cpu_disable_interrupt();
 
-	kprintf(msg);
+	kprintf("%s\n", msg);
+
+	arch_print_stack();
 
 	while (1) {
 		cpu_halt();