[PATCH] i386: add option to show more code in oops reports

Sometimes developers need to see more object code in an oops report,
e.g. when kernel may be corrupted at runtime.

Add the "code_bytes" option for this.
Signed-off-by: Chuck Ebbert <cebbert@redhat.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Documentation/kernel-parameters.txt

@@ -364,6 +364,11 @@ and is between 256 and 4096 characters. It is defined in the file
 			clocksource is not available, it defaults to PIT.
 			Format: { pit | tsc | cyclone | pmtmr }
 
+	code_bytes	[IA32] How many bytes of object code to print in an
+			oops report.
+			Range: 0 - 8192
+			Default: 64
+
 	disable_8254_timer
 	enable_8254_timer
 			[IA32/X86_64] Disable/Enable interrupt 0 timer routing

arch/i386/kernel/traps.c

@@ -94,6 +94,7 @@ asmlinkage void spurious_interrupt_bug(void);
 asmlinkage void machine_check(void);
 
 int kstack_depth_to_print = 24;
+static unsigned int code_bytes = 64;
 ATOMIC_NOTIFIER_HEAD(i386die_chain);
 
 int register_die_notifier(struct notifier_block *nb)
@@ -325,7 +326,8 @@ void show_registers(struct pt_regs *regs)
 	 */
 	if (in_kernel) {
 		u8 *eip;
-		int code_bytes = 64;
+		unsigned int code_prologue = code_bytes * 43 / 64;
+		unsigned int code_len = code_bytes;
 		unsigned char c;
 
 		printk("\n" KERN_EMERG "Stack: ");
@@ -333,14 +335,14 @@ void show_registers(struct pt_regs *regs)
 
 		printk(KERN_EMERG "Code: ");
 
-		eip = (u8 *)regs->eip - 43;
+		eip = (u8 *)regs->eip - code_prologue;
 		if (eip < (u8 *)PAGE_OFFSET ||
 			probe_kernel_address(eip, c)) {
 			/* try starting at EIP */
 			eip = (u8 *)regs->eip;
-			code_bytes = 32;
+			code_len = code_len - code_prologue + 1;
 		}
-		for (i = 0; i < code_bytes; i++, eip++) {
+		for (i = 0; i < code_len; i++, eip++) {
 			if (eip < (u8 *)PAGE_OFFSET ||
 				probe_kernel_address(eip, c)) {
 				printk(" Bad EIP value.");
@@ -1192,3 +1194,13 @@ static int __init kstack_setup(char *s)
 	return 1;
 }
 __setup("kstack=", kstack_setup);
+
+static int __init code_bytes_setup(char *s)
+{
+	code_bytes = simple_strtoul(s, NULL, 0);
+	if (code_bytes > 8192)
+		code_bytes = 8192;
+
+	return 1;
+}
+__setup("code_bytes=", code_bytes_setup);