lkml.org 
[lkml]   [2006]   [Sep]   [19]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] Linux Kernel Markers
* Martin Bligh (mbligh@google.com) wrote:
> How about we combine all three ideas together ...
>
> 1. Load modified copy of the function in question.
> 2. overwrite the first instruction of the routine with an int3 that
> does what you say (atomically)
> 3. Then overwrite the second instruction with a jump that's faster
> 4. Now atomically overwrite the int3 with a nop, and let the jump
> take over.
>

Very good idea.. However, overwriting the second instruction with a jump could
be dangerous on preemptible and SMP kernels, because we never know if a thread
has an IP in any of its contexts that would return exactly at the middle of the
jump. I think it would be doable to overwrite a 5+ bytes instruction with a NOP
non-atomically in all cases, but as the instructions nin the prologue seems to
be smaller :

prologue on x86
0: 55 push %ebp
1: 89 e5 mov %esp,%ebp
epilogue on x86
3: 5d pop %ebp
4: c3 ret

Then is can be a problem. Ideas are welcome.

Mathieu


OpenPGP public key: http://krystal.dyndns.org:8080/key/compudj.gpg
Key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2006-09-19 19:57    [W:0.529 / U:0.012 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site