Messages in this thread | | | Date | Wed, 20 Sep 2006 11:39:55 +0200 | From | Helge Hafting <> | Subject | Re: [PATCH] Linux Kernel Markers |
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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
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