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Bug #1: Issue 5406 identified an interesting case: defer iface.M() may end up calling a wrapper that copies an indirect receiver from the iface value and then calls the real M method. That's two calls down, not just one, and so recover() == nil always in the real M method, even during a panic. [For the purposes of this entire discussion, a wrapper's implementation is a function containing an ordinary call, not the optimized tail call form that is somtimes possible. The tail call does not create a second frame, so it is already handled correctly.] Fix this bug by introducing g->panicwrap, which counts the number of bytes on current stack segment that are due to wrapper calls that should not count against the recover check. All wrapper functions must now adjust g->panicwrap up on entry and back down on exit. This adds slightly to their expense; on the x86 it is a single instruction at entry and exit; on the ARM it is three. However, the alternative is to make a call to recover depend on being able to walk the stack, which I very much want to avoid. We have enough problems walking the stack for garbage collection and profiling. Also, if performance is critical in a specific case, it is already faster to use a pointer receiver and avoid this kind of wrapper entirely. Bug #2: The old code, which did not consider the possibility of two calls, already contained a check to see if the call had split its stack and so the panic-created segment was one behind the current segment. In the wrapper case, both of the two calls might split their stacks, so the panic-created segment can be two behind the current segment. Fix this by propagating the Stktop.panic flag forward during stack splits instead of looking backward during recover. Fixes #5406. R=golang-dev, iant CC=golang-dev https://golang.org/cl/13367052
28 lines
917 B
ArmAsm
28 lines
917 B
ArmAsm
// Copyright 2012 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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#include "../../cmd/ld/textflag.h"
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// makeFuncStub is the code half of the function returned by MakeFunc.
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// See the comment on the declaration of makeFuncStub in makefunc.go
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// for more details.
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// No argsize here, gc generates argsize info at call site.
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TEXT ·makeFuncStub(SB),(NOSPLIT|WRAPPER),$8
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MOVL DX, 0(SP)
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LEAL argframe+0(FP), CX
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MOVL CX, 4(SP)
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CALL ·callReflect(SB)
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RET
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// methodValueCall is the code half of the function returned by makeMethodValue.
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// See the comment on the declaration of methodValueCall in makefunc.go
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// for more details.
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// No argsize here, gc generates argsize info at call site.
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TEXT ·methodValueCall(SB),(NOSPLIT|WRAPPER),$8
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MOVL DX, 0(SP)
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LEAL argframe+0(FP), CX
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MOVL CX, 4(SP)
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CALL ·callMethod(SB)
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RET
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