YJIT: Invoke PosMarker callbacks only with solid positions
Previously, PosMarker callbacks ran even when the assembler failed to assemble its contents due to insufficient space. This was problematic because when Assembler::compile() failed, the callbacks were given positions that have no valid code, contrary to general expectation.
For example, we use a PosMarker callback to record VM instruction boundaries and patch in jumps to exits in case the guest program starts tracing, however, previously, we could record a location near the end of the code block, where there is no space to patch in jumps. I suspect this is the cause of the recent occurrences of rare random failures on GitHub Actions with the invariants.rs:529 "can rewrite existing code" message. --yjit-perf also uses PosMarker and had a similar issue.
Buffer the list of callbacks to fire, and only fire them when all code in the assembler are written out successfully. It's more intuitive this way.
Added by alanwu (Alan Wu) about 2 years ago
YJIT: Invoke PosMarker callbacks only with solid positions
Previously, PosMarker callbacks ran even when the assembler failed to
assemble its contents due to insufficient space. This was problematic
because when Assembler::compile() failed, the callbacks were given
positions that have no valid code, contrary to general expectation.
For example, we use a PosMarker callback to record VM instruction
boundaries and patch in jumps to exits in case the guest program starts
tracing, however, previously, we could record a location near the end of
the code block, where there is no space to patch in jumps. I suspect
this is the cause of the recent occurrences of rare random failures on
GitHub Actions with the invariants.rs:529 "can rewrite existing code"
message.
--yjit-perfalso uses PosMarker and had a similar issue.Buffer the list of callbacks to fire, and only fire them when all code
in the assembler are written out successfully. It's more intuitive this
way.