Re: [PATCH] Linux Kernel Markers

Helge Hafting
2006-09-20T09:43:21Z

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