Change stack walking to stop at a precise fp #9420
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Prior to this commit entry trampolines into wasm would record their stack pointer at the time of the function call to wasm and then this stack pointer was used to halt the stack walking process. The problem with this though is that due to the `tail` ABI it's possible that the callee will update the caller's stack pointer temporarily. This means that the recorded stack pointer at the time the trampoline called wasm may differ from the callee's idea of what the stack pointer is when a backtrace happens. To handle this condition when stack walking the frame pointer instead of the stack pointer is now recorded when wasm is invoked. This frame pointer is a trusted value as it's managed by Cranelift itself. This additionally enables the stop condition for frame walking to be a precise "it must be this value" condition. Put together this commit fixes an issue where when `return_call` is used it's possible for the initial few frames of the stack to get lost in stack traces. After this the frame pointer chain should always be precisely walked in its entirety, even in the face of different numbers of arguments and parameters as `return_call` instructions are executed.
This commit extends the preexisting `stacks` fuzzer with a few new features: * `return_call` instructions are now generated * functions may have both params/results to exercise logic around stack adjustments and how that might affect a stack trace
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Prior to this commit entry trampolines into wasm would record their
stack pointer at the time of the function call to wasm and then this
stack pointer was used to halt the stack walking process. The problem
with this though is that due to the
tailABI it's possible that thecallee will update the caller's stack pointer temporarily. This means
that the recorded stack pointer at the time the trampoline called wasm
may differ from the callee's idea of what the stack pointer is when a
backtrace happens.
To handle this condition when stack walking the frame pointer instead of
the stack pointer is now recorded when wasm is invoked. This frame
pointer is a trusted value as it's managed by Cranelift itself. This
additionally enables the stop condition for frame walking to be a
precise "it must be this value" condition.
Put together this commit fixes an issue where when
return_callis usedit's possible for the initial few frames of the stack to get lost in
stack traces. After this the frame pointer chain should always be
precisely walked in its entirety, even in the face of different numbers
of arguments and parameters as
return_callinstructions are executed.