v8: only remove prefix when mapping is removed #45
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Gandem
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prior to this change we were tracking generation number (i.e. count of SynchronizeMappings call where the object was found) for both mappings and prefixes. if the mapping did not change, we would not re-calculate prefixes for the mapping, hence we would not increase the generation of the prefix object. as such, we would end up cleaning the prefix on the second call of SynchronizeMappings (if mappings did not change), removing the prefix from the ebpf map, and making unwinding fail for PC in the JIT area. to fix this, we only track the generation for mappings. when mappings are removed, we computed all the prefixes associated to those mappings and we remove them. this should be safe because different mappings should have different prefixes.
nsavoire
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Sep 3, 2024
Signed-off-by: Florian Lehner <[email protected]>
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Fix unwinding for JIT code in NodeJS, when
SynchronizeMappingsis called multiple times for the same process.If the first frames being unwinded for a new NodeJS PID are JIT frames, we're going to both:
If the agent has already treated PID processing for the PID start, it will re-trigger PID processing for the unwinding failure, hence call
SynchronizeMappings()twice for the same NodeJS PID with the same mappings.This in turn, will trigger the bug explained in the commit description below: 707fc7b