i386: handle_BUG(): don't print garbage if debug info unavailable

handle_BUG() tries to print file and line number even when they're not available (CONFIG_DEBUG_BUGVERBOSE is not set.) Change this to print a message stating info is unavailable instead of printing a misleading message.

Signed-off-by Chuck Ebbert <[email protected]>

---

Compile tested only, with/without CONFIG_DEBUG_BUGVERBOSE.

 arch/i386/kernel/traps.c |   20 +++++++++++++-------
 1 files changed, 13 insertions(+), 7 deletions(-)

arch/i386/kernel/traps.c +11 -5

@@ -324,13 +324,14 @@ void show_registers(struct pt_regs *regs
 
 static void handle_BUG(struct pt_regs *regs)
 {
+	unsigned long eip = regs->eip;
 	unsigned short ud2;
+
+#ifdef CONFIG_DEBUG_BUGVERBOSE
 	unsigned short line;
 	char *file;
 	char c;
-	unsigned long eip;
-
-	eip = regs->eip;
+#endif
 
 	if (eip < PAGE_OFFSET)
 		goto no_bug;

@@ -338,21 +339,26 @@ static void handle_BUG(struct pt_regs *r
 		goto no_bug;
 	if (ud2 != 0x0b0f)
 		goto no_bug;
+	printk(KERN_EMERG "------------[ cut here ]------------\n");
+
+#ifdef CONFIG_DEBUG_BUGVERBOSE
 	if (__get_user(line, (unsigned short __user *)(eip + 2)))
-		goto bug;
+		goto no_info;
 	if (__get_user(file, (char * __user *)(eip + 4)) ||
 		(unsigned long)file < PAGE_OFFSET || __get_user(c, file))
 		file = "<bad filename>";
 
-	printk(KERN_EMERG "------------[ cut here ]------------\n");
 	printk(KERN_EMERG "kernel BUG at %s:%d!\n", file, line);
+#else
+	goto no_info;
+#endif
 

I think we can do it a lot more tidily.

static void handle_BUG(struct pt_regs *regs)

{
	unsigned long eip = regs->eip;
	unsigned short ud2;

	if (eip < PAGE_OFFSET)
		return;
	if (__get_user(ud2, (unsigned short __user *)eip))
		return;
	if (ud2 != 0x0b0f)
		return;

	printk(KERN_EMERG "------------[ cut here ]------------\n");

#ifdef CONFIG_DEBUG_BUGVERBOSE
	do {
		unsigned short line;
		char *file;
		char c;

		if (__get_user(line, (unsigned short __user *)(eip + 2)))
			break;
		if (__get_user(file, (char * __user *)(eip + 4)) ||
		    (unsigned long)file < PAGE_OFFSET || __get_user(c, file))
			file = "<bad filename>";

		printk(KERN_EMERG "kernel BUG at %s:%d!\n", file, line);
		return;
	} while (0);
#endif
	printk(KERN_EMERG "Kernel BUG at [verbose debug info unavailable]\n");
}

OK?

OK but you don't need a do/while(0) here.

Quoted 2 lines · Nick Piggin

OK but you don't need a do/while(0) here.

Actually, the way Andrew wrote it, it _is_ needed. It does two things:

- it's the block scope that allows the private variables
- if the "get_user()" fails, the "break" means that you don't have to have a goto.

That said, I think it's wrong to use "__get_user()", which can hang on the MM semaphore if something is bogus. We should probably mark us as being "in_atomic()" to make sure that the page fault handler, if it is entered, will not try to get the semaphore or page anything in.

This?