Fix preservation of the sigaltstack on macOS #2676
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This commit fixes an issue discovered in the wasmtime-go bindings when the Go runtime was crashing on macOS only when running wasm code that trapped. It turns out that our switch to `siglongjmp` from `longjmp` actually broke macOS! This breakage happens because all subsequent signals after the first signal are all delivered on the main stack, not the sigaltstack, even if the sigaltstack is configured. This causes the Go runtime to crash since it expects to run on the sigaltstack. The fix in this commit is to actually return from the signal handler to trigger the kernel's updating of the sigaltstack no longer being in use. Before we return, however, we configure the register context to return to to call some custom code which immediately does the unwind we would otherwise have done. This works around the issue on macOS hopefully without adding too many portability problems. Ideally this will all go away as well with bytecodealliance#2632 as well.
peterhuene
approved these changes
Feb 23, 2021
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This commit fixes an issue discovered in the wasmtime-go bindings when
the Go runtime was crashing on macOS only when running wasm code that
trapped. It turns out that our switch to
siglongjmpfromlongjmpactually broke macOS! This breakage happens because all subsequent
signals after the first signal are all delivered on the main stack, not
the sigaltstack, even if the sigaltstack is configured. This causes the
Go runtime to crash since it expects to run on the sigaltstack.
The fix in this commit is to actually return from the signal handler to
trigger the kernel's updating of the sigaltstack no longer being in use.
Before we return, however, we configure the register context to return
to to call some custom code which immediately does the unwind we would
otherwise have done. This works around the issue on macOS hopefully
without adding too many portability problems. Ideally this will all go
away as well with #2632 as well.