On Wed, 22 Jul 2009, Krzysztof Oledzki wrote:
On Tue, 21 Jul 2009, Linus Torvalds wrote:
On Tue, 21 Jul 2009, Linus Torvalds wrote:
Anyway, I bet we can work around the compiler bug by just changing the
type of "i" from "unsigned char" to be a plain "int".
IOW, like this.
Linus
---
drivers/video/fbmon.c | 4 ++--
1 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/video/fbmon.c b/drivers/video/fbmon.c
index 5c1a2c0..af4a15c 100644
--- a/drivers/video/fbmon.c
+++ b/drivers/video/fbmon.c
@@ -256,8 +256,8 @@ static void fix_edid(unsigned char *edid, int fix)
static int edid_checksum(unsigned char *edid)
{
- unsigned char i, csum = 0, all_null = 0;
- int err = 0, fix = check_edid(edid);
+ unsigned csum = 0, all_null = 0;
+ int i, err = 0, fix = check_edid(edid);
if (fix)
fix_edid(edid, fix);
Wow! You guys rock! ;)
Indeed, this simple change is enough to make my kernel bootable. However, there is still something wrong. My console is now 80x30 instead of 128x48:
-Console: switching to colour frame buffer device 128x48
+Console: switching to colour frame buffer device 80x30
So, it looks like the loop may be still miscompiled.
The kernel is here:
http://noc.axelspringer.pl/no-strict-overflow-vs-wrapv/vmlinux-fno-strict-overflow-fixed.bz2
OK, by adding a simple debug printk I'm now sure that the problem is indeed in the loop:
--- linux-2.6.27.27-a/drivers/video/fbmon.c 2009-07-20 05:45:22.000000000 +0200
+++ linux-2.6.27.27-b/drivers/video/fbmon.c 2009-07-22 09:45:34.000000000 +0200
@@ -272,6 +272,8 @@
err = 1;
}
+ printk("edid_checksum debug: csum=%u, all_null=%u, err=%d\n", csum, all_null, err);
+
return err;
}
Here is a diff between a good and a bad kernel:
-edid_checksum debug: csum=0, all_null=255, err=1
-edid_checksum debug: csum=0, all_null=255, err=1
-Console: switching to colour frame buffer device 128x48
+edid_checksum debug: csum=6400, all_null=255, err=0
+Console: switching to colour frame buffer device 80x30
In the good one the function is called twice and it returns err=1 (==OK). In the bad kernel it returns 0 because csum!=0x00 (==6400).