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Fix dlfilter filtering out trace errors #265

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merged 2 commits into from
Nov 16, 2022
Merged

Fix dlfilter filtering out trace errors #265

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4d45ced
Make dlfilter backend less aggressive about filtering out errors
Xyene Nov 14, 2022
bb9733f
Revert "Disable dlfilter by default"
Xyene Nov 14, 2022
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6 changes: 2 additions & 4 deletions core/env_vars.ml
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Original file line number Diff line number Diff line change
Expand Up @@ -21,10 +21,8 @@ let debug = Option.is_some (Unix.getenv "MAGIC_TRACE_DEBUG")
features of magic-trace. *)
let experimental = Option.is_some (Unix.getenv "MAGIC_TRACE_EXPERIMENTAL")

(* magic-trace's dlfilter integration is busted right now, see #246. Also:

When tracing the kernel on certain systems, perf only has root access when
(* When tracing the kernel on certain systems, perf only has root access when
being run with a specific set of flags. Since this does not include
[--dlfilter], this environment variable allows the user to forcibly disable
filtering. *)
let no_dlfilter = Option.is_none (Unix.getenv "MAGIC_TRACE_ENABLE_DLFILTER")
let no_dlfilter = Option.is_some (Unix.getenv "MAGIC_TRACE_NO_DLFILTER")
8 changes: 6 additions & 2 deletions src/perf_dlfilter.c
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Expand Up @@ -13,10 +13,14 @@ int filter_event_early(void *data, const struct perf_dlfilter_sample *sample,
perf_dlfilter_fns.resolve_ip(ctx);
const struct perf_dlfilter_al *resolved_addr =
perf_dlfilter_fns.resolve_addr(ctx);
if (!resolved_ip || !resolved_ip->sym || !resolved_addr ||
!resolved_addr->sym ||

// Only filter out events we for sure don't want. It's better to be less aggressive than
// too aggressive, as being too aggressive will lead to broken traces, while being not
// aggressive enough just makes things slower.
if (resolved_ip && resolved_ip->sym && resolved_addr && resolved_addr->sym &&
strcmp(resolved_ip->sym, resolved_addr->sym) == 0) {
return 1;
}

return 0;
}