Add support for easily fuzzing cg_gcc with rustlantis
#688
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UGH, it looks like I anciently included some unrelated changes. |
FractalFir
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Hopefully, should be good to review now. |
antoyo
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May 28, 2025
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Fixed the issues + added a few more detailed comments. Should be OK to review again now. |
antoyo
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May 28, 2025
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Should be all ready for merge now. |
antoyo
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May 28, 2025
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Thanks a lot for the amazing work! |
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This PR adds a new
ycommand:./y.sh fuzz.This command clones the rustlantis repo, and uses it to generate Rust programs to fuzz
cg_gccwith.It takes in 3 optional arguments: search space start(
--start), search space length(--count), and the parallelism(--jobs/-j).By default, the fuzzer will search the first 100 programs(this takes about a minute, and functions as a small test for more obscure semantics of rust, like NaN handling).
The script compiles programs with LLVM debug mode and GCC release mode, and then compares the result of their execution. If a compiler error occurs, or there is a runtime difference between the two backends, a message will be displayed, and the problematic source file will be copied over to either
target/fuzz/compiletime_errorortarget/fuzz/runtime_error.The fuzzer script respects
CG_RUSTFLAGS, which should allow us to test things like software floating point emulation, or 128 bit intiger emulation. We can also enable UB checks.Limitations
rustlantisdoes not support 32 bit systems without patches , so we can't fuzz on 32 bit platforms.Additonally, on platforms not supported by LLVM, we have nothing to compare to. We could compare against debug GCC runs, but that may miss things.
We might consider adding support for cross compilation / emulation, and compare scripts run on x86_64 with scripts run elsewhere.