…oid truncation When generating stacks, the runtime automatically expands inline functions to inline all inline frames in the stack. However, due to the stack size limit, the final frame may be truncated in the middle of several inline frames at the same location. As-is, we assume that the final frame is a normal function, and emit and cache a Location for it. If we later receive a complete stack frame, we will first use the cached Location for the inlined function and then generate a new Location for the "caller" frame, in violation of the pprof requirement to merge inlined functions into the same Location. As a result, we: 1. Nondeterministically may generate a profile with the different stacks combined or split, depending on which is encountered first. This is particularly problematic when performing a diff of profiles. 2. When split stacks are generated, we lose the inlining information. We avoid both of these problems by performing a second expansion of the last stack frame to recover additional inline frames that may have been lost. This expansion is a bit simpler than the one done by the runtime because we don't have to handle skipping, and we know that the last emitted frame is not an elided wrapper, since it by definition is already included in the stack. Fixes #37447 Change-Id: If3ca2af25b21d252cf457cc867dd932f107d4c61 Reviewed-on: https://go-review.googlesource.com/c/go/+/221577 Run-TryBot: Michael Pratt <mpratt@google.com> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Heschi Kreinick <heschi@google.com> Reviewed-by: Keith Randall <khr@golang.org> Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com> (cherry picked from commit fadbf74) Reviewed-on: https://go-review.googlesource.com/c/go/+/222762

runtime/pprof: inline frames may not use combined location [1.14 backport] #37447

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