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runtime: backport CL 31138 #18333

aclements opened this issue Dec 15, 2016 · 2 comments


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commented Dec 15, 2016

If we do a 1.7.5 release, backport CL 31138, which fixes #16331 and #17471.

@aclements aclements added this to the Go1.7.5 milestone Dec 15, 2016


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commented Jan 24, 2017

CL mentions this issue.

gopherbot pushed a commit that referenced this issue Jan 25, 2017

[release-branch.go1.7] runtime: fix getArgInfo for deferred reflectio…
…n calls

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

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
Run-TryBot: Austin Clements <>
TryBot-Result: Gobot Gobot <>
Reviewed-by: Keith Randall <>
Run-TryBot: Brad Fitzpatrick <>
Reviewed-by: Austin Clements <>

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commented Jan 26, 2017

Submitted to 1.7 branch.

@bradfitz bradfitz closed this Jan 26, 2017

@golang golang locked and limited conversation to collaborators Jan 26, 2018

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