bpf tracing multi-link supporting

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" summary

Implements a global trampoline that uses an rhashtable to map target function addresses to metadata (BPF programs, cookie, arg count), letting one BPF program attach to many functions instead of cloning per-function instances. Built with rhashtable plus naked functions and C on x86_64, it cuts large-scale attach time from tens of minutes to under 1 second for 50k functions. Limits: no static args over six, no jump model, per-call hash lookup adds runtime overhead (bench shows ~25% hit in one case) and falls back to per-function trampolines when needed.

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" chapters (12)

1. 0:00Introduction and overview
2. 1:50BPF trampoline basics
3. 3:43Limitations of current tracing
4. 5:09Ftrace and trampoline attachment
5. 8:40Single ftrace object optimization
6. 9:03BPF multi-link concept
7. 12:40Function metadata design
8. 15:16Attachment during loading time
9. 17:02BPF global link implementation
10. 19:30Modifying trampoline updates
11. 21:20Performance and issues
12. 25:24Q&A discussion