93 lines
3.6 KiB
Plaintext
93 lines
3.6 KiB
Plaintext
|
[Sat Mar 2 10:32:33 PST 1996 KERNEL_BUG-HOWTO lm@sgi.com (Larry McVoy)]
|
||
|
|
|
||
|
|
This is how to track down a bug if you know nothing about kernel hacking.
|
||
|
|
It's a brute force approach but it works pretty well.
|
||
|
|
|
||
|
|
You need:
|
||
|
|
|
||
|
|
. A reproducible bug - it has to happen predictably (sorry)
|
||
|
|
. All the kernel tar files from a revision that worked to the
|
||
|
|
revision that doesn't
|
||
|
|
|
||
|
|
You will then do:
|
||
|
|
|
||
|
|
. Rebuild a revision that you believe works, install, and verify that.
|
||
|
|
. Do a binary search over the kernels to figure out which one
|
||
|
|
introduced the bug. I.e., suppose 1.3.28 didn't have the bug, but
|
||
|
|
you know that 1.3.69 does. Pick a kernel in the middle and build
|
||
|
|
that, like 1.3.50. Build & test; if it works, pick the mid point
|
||
|
|
between .50 and .69, else the mid point between .28 and .50.
|
||
|
|
. You'll narrow it down to the kernel that introduced the bug. You
|
||
|
|
can probably do better than this but it gets tricky.
|
||
|
|
|
||
|
|
. Narrow it down to a subdirectory
|
||
|
|
|
||
|
|
- Copy kernel that works into "test". Let's say that 3.62 works,
|
||
|
|
but 3.63 doesn't. So you diff -r those two kernels and come
|
||
|
|
up with a list of directories that changed. For each of those
|
||
|
|
directories:
|
||
|
|
|
||
|
|
Copy the non-working directory next to the working directory
|
||
|
|
as "dir.63".
|
||
|
|
One directory at time, try moving the working directory to
|
||
|
|
"dir.62" and mv dir.63 dir"time, try
|
||
|
|
|
||
|
|
mv dir dir.62
|
||
|
|
mv dir.63 dir
|
||
|
|
find dir -name '*.[oa]' -print | xargs rm -f
|
||
|
|
|
||
|
|
And then rebuild and retest. Assuming that all related
|
||
|
|
changes were contained in the sub directory, this should
|
||
|
|
isolate the change to a directory.
|
||
|
|
|
||
|
|
Problems: changes in header files may have occurred; I've
|
||
|
|
found in my case that they were self explanatory - you may
|
||
|
|
or may not want to give up when that happens.
|
||
|
|
|
||
|
|
. Narrow it down to a file
|
||
|
|
|
||
|
|
- You can apply the same technique to each file in the directory,
|
||
|
|
hoping that the changes in that file are self contained.
|
||
|
|
|
||
|
|
. Narrow it down to a routine
|
||
|
|
|
||
|
|
- You can take the old file and the new file and manually create
|
||
|
|
a merged file that has
|
||
|
|
|
||
|
|
#ifdef VER62
|
||
|
|
routine()
|
||
|
|
{
|
||
|
|
...
|
||
|
|
}
|
||
|
|
#else
|
||
|
|
routine()
|
||
|
|
{
|
||
|
|
...
|
||
|
|
}
|
||
|
|
#endif
|
||
|
|
|
||
|
|
And then walk through that file, one routine at a time and
|
||
|
|
prefix it with
|
||
|
|
|
||
|
|
#define VER62
|
||
|
|
/* both routines here */
|
||
|
|
#undef VER62
|
||
|
|
|
||
|
|
Then recompile, retest, move the ifdefs until you find the one
|
||
|
|
that makes the difference.
|
||
|
|
|
||
|
|
Finally, you take all the info that you have, kernel revisions, bug
|
||
|
|
description, the extent to which you have narrowed it down, and pass
|
||
|
|
that off to whomever you believe is the maintainer of that section.
|
||
|
|
A post to linux.dev.kernel isn't such a bad idea if you've done some
|
||
|
|
work to narrow it down.
|
||
|
|
|
||
|
|
If you get it down to a routine, you'll probably get a fix in 24 hours.
|
||
|
|
|
||
|
|
My apologies to Linus and the other kernel hackers for describing this
|
||
|
|
brute force approach, it's hardly what a kernel hacker would do. However,
|
||
|
|
it does work and it lets non-hackers help fix bugs. And it is cool
|
||
|
|
because Linux snapshots will let you do this - something that you can't
|
||
|
|
do with vendor supplied releases.
|
||
|
|
|