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cf28e5cc9d
when compiling f(a, b, c), we do something like: *(SP+0) = eval(a) *(SP+8) = eval(b) *(SP+16) = eval(c) call f If one of those evaluations is later determined to unconditionally panic (say eval(b) in this example), then the call is deadcode eliminated. But any previous argument write (*(SP+0)=... here) is still around. Becuase we only compute the size of the outarg area for calls which are still around at the end of optimization, the space needed for *(SP+0)=v is not accounted for and thus the outarg area may be too small. The fix is to make sure that we evaluate any potentially panicing operation before we write any of the args to the stack. It turns out that fix is pretty easy, as we already have such a mechanism available for function args. We just need to extend it to possibly panicing args as well. The resulting code (if b and c can panic, but a can't) is: tmpb = eval(b) *(SP+16) = eval(c) *(SP+0) = eval(a) *(SP+8) = tmpb call f This change tickled a bug in how we find the arguments for intrinsic calls, so that latent bug is fixed up as well. Update #16760. Change-Id: I0bf5edf370220f82bc036cf2085ecc24f356d166 Reviewed-on: https://go-review.googlesource.com/32551 Reviewed-by: Cherry Zhang <cherryyz@google.com>
43 lines
795 B
Go
43 lines
795 B
Go
// run
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// Copyright 2016 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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// Make sure we don't start marshaling (writing to the stack)
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// arguments until those arguments are evaluated and known
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// not to unconditinally panic. If they unconditionally panic,
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// we write some args but never do the call. That messes up
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// the logic which decides how big the argout section needs to be.
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package main
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type W interface {
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Write([]byte)
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}
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type F func(W)
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func foo(f F) {
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defer func() {
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if r := recover(); r != nil {
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usestack(1000)
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}
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}()
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f(nil)
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}
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func main() {
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foo(func(w W) {
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var x []string
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w.Write([]byte(x[5]))
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})
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}
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func usestack(n int) {
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if n == 0 {
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return
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}
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usestack(n - 1)
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}
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