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Rohan Kumar 2023-04-17 00:07:50 -07:00
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content/notes/clang-supports-wiping-call-used-registers.md
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---
title: "Clang supports wiping call-used registers"
date: 2023-04-17T00:01:52-07:00
syndicatedCopies:
- title: 'The Fediverse'
url: 'https://pleroma.envs.net/notice/AUjf1wCr0xk0yCVpKK'
---
Here's a compiler flag that slipped my notice: [Clear Linux has `-fzero-call-used-regs=used` in its `CFLAGS`](https://github.com/clearlinux/autospec/blob/46c9d3a49c51235efef62280deb9136f2ee9b203/autospec/specfiles.py#L542) for security-sensitive x86_64 packages, wiping call-used registers on return to protect against ROP exploits. In my benchmarks, there was almost no perf difference between `skip`, `used-gpr` and `used` which is surprising; I thought that this would really hurt instruction cache optimization.