• Austin Clements's avatar
    [release-branch.go1.7] runtime: fix getArgInfo for deferred reflection calls · efdb1813
    Austin Clements authored
    Fixes #18333 (backport)
    
    getArgInfo for reflect.makeFuncStub and reflect.methodValueCall is
    necessarily special. These have dynamically determined argument maps
    that are stored in their context (that is, their *funcval). These
    functions are written to store this context at 0(SP) when called, and
    getArgInfo retrieves it from there.
    
    This technique works if getArgInfo is passed an active call frame for
    one of these functions. However, getArgInfo is also used in
    tracebackdefers, where the "call" is not a true call with an active
    stack frame, but a deferred call. In this situation, getArgInfo
    currently crashes because tracebackdefers passes a frame with sp set
    to 0. However, the entire approach used by getArgInfo is flawed in
    this situation because the wrapper has not actually executed, and
    hence hasn't saved this metadata to any stack frame.
    
    In the defer case, we know the *funcval from the _defer itself, so we
    can fix this by teaching getArgInfo to use the *funcval context
    directly when its available, and otherwise get it from the active call
    frame.
    
    While we're here, this commit simplifies getArgInfo a bit by making it
    play more nicely with the type system. Rather than decoding the
    *reflect.methodValue that is the wrapper's context as a *[2]uintptr,
    just write out a copy of the reflect.methodValue type in the runtime.
    
    Fixes #16331. Fixes #17471.
    
    Change-Id: I81db4d985179b4a81c68c490cceeccbfc675456a
    Reviewed-on: https://go-review.googlesource.com/31138
    Run-TryBot: Austin Clements <austin@google.com>
    TryBot-Result: Gobot Gobot <gobot@golang.org>
    Reviewed-by: 's avatarKeith Randall <khr@golang.org>
    Reviewed-on: https://go-review.googlesource.com/35638
    Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
    Reviewed-by: 's avatarAustin Clements <austin@google.com>
    efdb1813
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