Re: [RFC PATCH v2 08/11] ptwrite uprobes: Support instruction punning
From: sashiko-bot@kernel.org
Date: 2026-09-17 23:27:02
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linux-perf-users
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! -- Sashiko AI review · https://sashiko.dev/#/patchset/20260917230127.924985-2-ak@kernel.org?part=8