Re: [PATCH] Linux Kernel Markers

[Helge Hafting]

S. P. Prasanna wrote:
> > Yes, that's simple. but slower, as you have a double jump. Probably
> > a damned sight faster than int3 though.
> >
> > M.
> >     
>
> The advantage of using int3 over jmp to launch the instrumented
> module is that int3 (or breakpoint in most architectures) is an
> atomic operation to insert.
>   
Yes, 5 bytes is not an atomic write except on 64-bit. So a race is possible.

How about this workaround:
1. Overwrite the start of the function with a hlt, which is atomic.
2. Write that 5-byte jump after the hlt.
3. Overwrite the hlt with nop so things will work
4. interrupt any cpus that got stuck on the hlt - or just wait for the 
timer.

Helge Hafting

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/