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{
  "commit": "5fb8d6f4fe2b120981f4800fdb085c19882fa899",
  "tree": "9593c19d44bc7a2a4686fc2164885f98b57f1875",
  "parents": [
    "1f1abaeafbc4881c3e7eba0e194b241d91f51643"
  ],
  "author": {
    "name": "David Reveman",
    "email": "reveman@meta.com",
    "time": "Tue Mar 10 18:45:48 2026 -0700"
  },
  "committer": {
    "name": "David Reveman",
    "email": "reveman@meta.com",
    "time": "Wed Mar 11 11:19:09 2026 -0400"
  },
  "message": "EXPERIMENT: Add nongnu.org libunwind as alternative unwinding backend\n\nNOT FOR REVIEW\n\nAdd optional support for nongnu.org libunwind as an alternative to\nAndroid\u0027s libunwindstack for DWARF-based stack unwinding in both\ntraced_perf and heapprofd. Selected at build time via the GN flag\nenable_perfetto_libunwind.\n\nlibunwindstack pulls in several vendored Android dependencies\n(android-libprocinfo, android-libbase, bionic kernel UAPI headers)\nmaking it difficult to use perfetto\u0027s profiling tools on non-Android\nplatforms. With this change, setting enable_perfetto_libunwind\u003dtrue\nbuilds everything without any libunwindstack dependency.\n\nThe refactoring introduces:\n\n- An UnwindBackend interface with two implementations:\n  LibunwindstackBackend (wrapping existing logic) and LibunwindBackend\n  (using libunwind\u0027s remote API with custom accessors for sampled\n  stack overlays and /proc/pid/mem).\n- Backend-agnostic types (UnwindFrame, UnwindErrorCode, RegisterData)\n  replacing direct use of unwindstack types throughout the pipeline.\n- Perfetto-owned register capture (regs_common.h, regs_local.h, .S)\n  so the heapprofd client no longer depends on libunwindstack for\n  AsmGetRegs, ArchEnum, or register constants.\n- Wire protocol updated to use Perfetto-owned types, maintaining ABI\n  compatibility with existing register layouts.\n- Bookkeeping simplified to use UnwindFrame directly, removing the\n  intermediate unwindstack::FrameData conversion layer.\n\nAlso fixes nongnu libunwind\u0027s Gget_proc_info_in_range.c which\nincorrectly dereferenced a remote .eh_frame_hdr address as a local\npointer, causing crashes during remote unwinding.\n\nlibunwind v1.8.0 is vendored via tools/install-build-deps and built\nfrom source with UNW_REMOTE_ONLY (no local unwinding assembly).\nPre-baked config headers live in buildtools/nongnu_libunwind_config/.\n\nOn non-Android Linux standalone builds, enable_perfetto_libunwind\ndefaults to true.\n",
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