Re: [RFC PATCH v2 08/11] ptwrite uprobes: Support instruction punning

[sashiko-bot@kernel.org]

> The previous ptwrite instrumentation only worked on 5 byte+ nops because
> it needs to patch in a 5 byte branch.
> 
> However that is somewhat limiting because it means most code cannot
> be probed. Use a simplified variant of the instruction
> punning technique from Chamith et al. "Instruction Punning: Lightweight
> instrumentation for x86-64". Patch only the one-byte branch opcode and
> reuse the existing 4 following bytes in the code as the branch target.
> 
> If someone branches to the remaining bytes they are still executed
> in the original way because they didn't change.
> 
> This requires placing a target trampoline page at the right address. If
> the area is not available or points to kernel space it doesn't work.
> 
> [ ... ]
> The punning technique could be also used with optimized
> uprobes, but this patch only applies it to ptwrite probes.
> 
> Assisted-by: omp:gpt-5.6-luna
> Signed-off-by: Andi Kleen <ak@kernel.org>

Sashiko has reviewed this patch and found no issues. It looks great!

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Sashiko AI review · https://sashiko.dev/#/patchset/20260917230127.924985-2-ak@kernel.org?part=8