Handle srem properly when avoid_div_traps is false.
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The codegen for div/rem ops has two modes, depending on the `avoid_div_traps` flag: it can either do all checks for trapping conditions explicitly, and use explicit trap instructions, then use a hardware divide instruction that will not trap (`avoid_div_traps == true`); or it can run in a mode where a hardware FP fault on the divide instruction implies a Wasm trap (`avoid_div_traps == false`). Wasmtime uses the former while Lucet (for example) uses the latter. It turns out that because we run all our spec tests run under Wasmtime, we missed a spec corner case that fails in the latter: INT_MIN % -1 == 0 per the spec, but causes a trap with the x86 signed divide/remainder instruction. Hence, in Lucet, this specific remainder computation would incorrectly result in a Wasm trap. This PR fixes the issue by just forcing use of the explicit-checks implementation for `srem` even when `avoid_div_traps` is false.
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Mar 25, 2021
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The codegen for div/rem ops has two modes, depending on the
avoid_div_trapsflag: it can either do all checks for trappingconditions explicitly, and use explicit trap instructions, then use a
hardware divide instruction that will not trap (
avoid_div_traps == true);or it can run in a mode where a hardware FP fault on the divide
instruction implies a Wasm trap (
avoid_div_traps == false). Wasmtimeuses the former while Lucet (for example) uses the latter.
It turns out that because we run all our spec tests run under Wasmtime,
we missed a spec corner case that fails in the latter: INT_MIN % -1 == 0
per the spec, but causes a trap with the x86 signed divide/remainder
instruction. Hence, in Lucet, this specific remainder computation would
incorrectly result in a Wasm trap.
This PR fixes the issue by just forcing use of the explicit-checks
implementation for
sremeven whenavoid_div_trapsis false.