commit 4f919b63bcb065a11b687e4f9409ca2a359edc86
author Ryan Savitski <rsavitski@google.com> Sun Feb 27 16:36:46 2022 +0000
committer Ryan Savitski <rsavitski@google.com> Sun Feb 27 16:42:20 2022 +0000
tree b4427ed12f6150a4c912b1ffd67acbfadf2752fa
parent 23a2d49e1465799beaa2cdd34f5eb2e833e08d3d

profile_module: omit packets referencing invalid callstack internings

This came up with an older (Android R) trace with a ring buffer holding
the perf_sample packets. The first N perf_sample packets were
referencing internings that were overwritten by the buffer wrapping. The
rest of the packets were fully well-formed since the tracing config
requested periodic incremental state clears, so the profiler stopped
referencing the old internings later in the packet sequence.

Newer traced_perf builds use SEQ_NEEDS_INCREMENTAL_STATE sequence flag,
which avoids this case as the pre-incremental-reset packets don't reach
the profile module parsing stage.

Distinguishing this case from counter-only profiles ended up being
a bit tricky since those still reference a valid-but-empty callstack
with zero frames. I chose to depend on the fact that the implementation
always ends up setting the empty callstack's interning id to "1", as
it is also the sentinel root node in the interning trie.

Alternatively, we could make the stack_profile_tracker identify the
zero-frame callstack's id dynamically, but that's not necessary at this
point.

Change-Id: I4cc4efc1284672c40f9fe194c9744cb7607de354
Bug: 218988616