Set up mapid -> mapfd relocation - #1861
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danobi
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May 27, 2021 20:16
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looks good :) |
Setup code for relocation helper. The relocator will fixup each probe's bytecode with information better available at runtime (as opposed to during codegen).
We will need every map to have an ID in order to relocate map ID -> map FD in BPF_PSUEDO_MAP_FD loads.
Before it could return Some(nullptr) if the map wasn't actually present
This commit relocates map id -> map fd. This is desirable for multiple reasons: 1) Codegen should be independent as possible from runtime state such as which FD a map gets. The more independent it is, the easier it is to test codegen b/c we won't have to mock as much stuff out or configure the testing environment as much. 2) This is necessary to enable ahead of time compile bpftrace scripts as a map FD is not guaranteed to be the same value on another host. Thus, the runtime must relocate map ID -> map FD at load time.
This is no longer necessary as the mapid is placed into bytecode now. This is nicer b/c now tests can't forget to set next_mapfd_ = 1 before running the test.
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This PR begins the work on ahead-of-time (AOT) compiled bpftrace
scripts. More details on AOT are available here.
Details on relocation are in individual commit messages.
Checklist
docs/reference_guide.mdCHANGELOG.md