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runtime: badmorestackg0 is never called on wasm #63953

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mauri870 opened this issue Nov 5, 2023 · 2 comments · Fixed by ferrmin/go#697
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runtime: badmorestackg0 is never called on wasm #63953

mauri870 opened this issue Nov 5, 2023 · 2 comments · Fixed by ferrmin/go#697
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arch-wasm WebAssembly issues compiler/runtime Issues related to the Go compiler and/or runtime. FrozenDueToAge

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mauri870 commented Nov 5, 2023

While investigating crash stack on wasm, i found that badmorestackg0 is behind a condition that is never true.

go/src/runtime/asm_wasm.s

Lines 217 to 230 in d72f454

TEXT runtime·morestack(SB), NOSPLIT, $0-0
// R1 = g.m
MOVD g_m(g), R1
// R2 = g0
MOVD m_g0(R1), R2
// Cannot grow scheduler stack (m->g0).
Get g
Get R1
I64Eq
If
CALLNORESUME runtime·badmorestackg0(SB)
End

As you can see above, it is comparing g == R1, R1 being g.m. We should be comparing it to g0, which is stored in R2.

It is also present in 1.20 and 1.21, but I'm not sure if we need to backport this given that it is not a significant issue.
@mauri870 mauri870 added arch-wasm WebAssembly issues compiler/runtime Issues related to the Go compiler and/or runtime. labels Nov 5, 2023
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mauri870 commented Nov 5, 2023

Original behavior:

RuntimeError: memory access out of bounds
    at runtime.morestack (wasm://wasm/0370d90e:wasm-function[1436]:0x134e6f)
    at runtime.morestack_noctxt (wasm://wasm/0370d90e:wasm-function[1437]:0x134eab)
    at runtime.newstack (wasm://wasm/0370d90e:wasm-function[977]:0xe4596)
    at runtime.morestack (wasm://wasm/0370d90e:wasm-function[1436]:0x134e8d)
    at runtime.morestack_noctxt (wasm://wasm/0370d90e:wasm-function[1437]:0x134eab)
    at runtime.newstack (wasm://wasm/0370d90e:wasm-function[977]:0xe4596)
    at runtime.morestack (wasm://wasm/0370d90e:wasm-function[1436]:0x134e8d)
    at runtime.morestack_noctxt (wasm://wasm/0370d90e:wasm-function[1437]:0x134eab)
    at runtime.newstack (wasm://wasm/0370d90e:wasm-function[977]:0xe4596)
    at runtime.morestack (wasm://wasm/0370d90e:wasm-function[1436]:0x134e8d)

With the fix applied:

RuntimeError: memory access out of bounds
    at runtime.morestack (wasm://wasm/0370d90e:wasm-function[1436]:0x134e6f)
    at runtime.morestack_noctxt (wasm://wasm/0370d90e:wasm-function[1437]:0x134eab)
    at runtime.write1 (wasm://wasm/0370d90e:wasm-function[662]:0x9c78f)
    at runtime.write (wasm://wasm/0370d90e:wasm-function[1056]:0xfbefc)
    at runtime.badmorestackg0 (wasm://wasm/0370d90e:wasm-function[766]:0xad590)
    at runtime.morestack (wasm://wasm/0370d90e:wasm-function[1436]:0x134df1)
    at runtime.morestack_noctxt (wasm://wasm/0370d90e:wasm-function[1437]:0x134eab)
    at runtime.write1 (wasm://wasm/0370d90e:wasm-function[662]:0x9c78f)
    at runtime.write (wasm://wasm/0370d90e:wasm-function[1056]:0xfbefc)
    at runtime.badmorestackg0 (wasm://wasm/0370d90e:wasm-function[766]:0xad590)

@mauri870 mauri870 mentioned this issue Nov 5, 2023
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Change https://go.dev/cl/539840 mentions this issue: runtime: fix badmorestackg0 never called on wasm

@mauri870 mauri870 self-assigned this Nov 5, 2023
@ferrmin ferrmin mentioned this issue Nov 6, 2023
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