tarantool / luajit / 37769463606

88%

tarantool/master: 88%

Build Type

push

github

Committed by ligurio

Commit Message

Optionally return PC position in jit.util.tracesnap().

Suggested by Sergey Bronnikov.

(cherry picked from commit 8e6520a7a)

The optional `getpos` argument is needed for ljopt [1], a tool that
verifies the correctness of LuaJIT optimizations by translating the
recorded IR into SMT-LIB and checking the formulas with an SMT solver.
Traces often lack sufficient information for accurate modeling, so
ljopt extracts the address of the bytecode pointed to by the snapshot
directly from LuaJIT during execution.

The LuaJIT internal API includes the function `jit.util.tracesnap(tr,
sn)`. In principle, this function could be extended to return the
program counter (pc). This patch does exactly that: an optional third
argument is added, and when it is truthy the second value returned by
`jit.util.tracesnap()` is the PC position of the snapshot in the
bytecode of the function where the trace starts.

Also, the patch adds a test that records a root loop trace and
checks that the returned position is the `FORL` jump target (the
loop entry), that no position is returned without the optional
argument or with a false value, and that every snapshot of the
trace reports a valid bytecode offset.

1. https://github.com/ligurio/ljopt

Sergey Bronnikov:
* added the description and the test for the feature

Coverage Stats

12784 of 15771 branches covered (81.06%)

Branch coverage included in aggregate %.

6 of 6 new or added lines in 1 file covered. (100.0%)

11 existing lines in 3 files now uncovered.

21953 of 23565 relevant lines covered (93.16%)

3854444.62 hits per line