Debugging

A two-hour outage caused by a harmless-looking rule insertion into the wrong chain position, and what I learned about nftables evaluation

Tail call optimization, manual trampolines, and a crash that took me three days to trace to the optimizer

Dynamic linking on ELF is a two-step dance through the PLT and the GOT, and once you see it you cannot unsee it

A nil deref in a background worker crashed our whole service because Go's panic model doesn't care that you spawned a goroutine to handle errors safely

Give bisect a script that exits 0 for good and non-zero for bad. It'll do the rest.

A hash table that benchmarked beautifully in isolation was five times slower under realistic load, and L2 cache misses explained why

Undefined symbols, multiple definitions, and the weekend I finally understood how --as-needed and --no-undefined interact

I was sure one version of a hot loop was faster; I was wrong; it was the CPU making me look smart

Different tool, adjacent niche. Handy when the bug lives in libc-level behavior, not syscalls.

strace -k shows the stack that led to each syscall, not just the syscall itself.

Attaching perf to a JVM produces garbage unless you tell perf where the JIT-compiled symbols are.

Shipping a Go binary that loaded fine on Linux but segfaulted on macOS led me down a rabbit hole of executable file formats

pprof.Labels lets you tag goroutines and filter flamegraphs by tag.

MONITOR prints every command the server handles. Very tempting. Very bad for prod.

A CPU profile pointed at a line with a simple map lookup, and pprof's disasm view sent me down a real rabbit hole