JIT: make Wasm frames that call a finally unwindable

[lewing]

On Wasm, genCallFinally calls the finally funclet but did not mark the calling function as needing an unwindable frame. genCallInstruction and genEmitHelperCall both call ensureCurrentFuncIsUnwindable(); genCallFinally was the only call emitter that did not.

When the callfinally is a method's only call, the prolog never stores the R2R function table index at $fp[0]. If the finally throws, unwinding out of the funclet reads a stale value from that slot. GetWasmVirtualIPFromFunctionTableIndex returns 0, the walk treats the caller as non-R2R, and the exception is reported as unhandled instead of reaching the caller's catch. A GC stack walk while the finally runs goes through the same broken frame.

This hits b51875, where the finally never returns. It also hits a finally that returns but is not cloned onto the normal path, for example under MinOpts.

Change

genCallFinally now calls ensureCurrentFuncIsUnwindable(). The prolog is generated after block codegen, so the flag takes effect. fgWasmVirtualIP already creates the function-index local for any method with a BBJ_CALLFINALLY. Funclets that call a finally were already unwindable.

No new test: b51875 and the JIT/Methodical runners already cover this under browser-wasm R2R (see below).

Validation

browser-wasm, Checked, src/tests/run.sh wasm checked --runcrossgen2tests, comparing the JIT with and without this fix (the JIT sources otherwise match):

Tests	Without fix	With fix
--tree=JIT/Regression --runner-filter=Regression_8 (b51875)	Unhandled exception. System.Exception, runner aborts	13/13 pass, including b51875.AA.TestEntryPoint
--tree=JIT/Methodical (6 runners)	All 6 runners crash within their first 4 tests (corrupted state after the failed unwind)	All 6 complete: 1968 total, 1924 passed, 22 failed, 22 skipped

The 22 JIT/Methodical failures are out-of-process explicit/* tests (refloc_*, refarg_box_f8, rotate_u2), which fail on an assertion in the out-of-process runner. There is no baseline for them because every runner crashed before reaching them without the fix. This change only affects codegen for calls to a finally.

JIT disassembly confirms the main method prolog now stores the function index.

Not run: Regression_PdbOnly_r_2, which contains the other copy of b51875.

Resolves #134975

Note

This PR description was generated with GitHub Copilot.

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