APS5_SAMPLE_WORKER=<file> now also writes <file stem>.collapsed.txt: one
"frame;...;frame count" line per distinct stack of queue worker 0, root
first, frames as module+0xRVA, which speedscope.app and flamegraph.pl
open. Walks go up to 64 frames, and nothing allocates while the worker is
suspended.
The libraries are built with -fno-asynchronous-unwind-tables, so most of
their functions have no .pdata entry, only a DWARF record in .ehfram, and a
walk ended at the first such frame. The worker's walk now steps those
frames through their record, with the CIE/FDE decoding and the call frame
instructions of libc's unwinder, which move from Unwind.cpp into its
header unchanged. A module is indexed after the worker resumes, the first
time a walk meets it, and every register the step restores is read inside
the worker's stack. The process sampler (APS5_SAMPLE_THREADS) keeps its 12
frames through .pdata.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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