diff options
author | Austin Clements <austin@google.com> | 2020-11-11 15:33:39 -0500 |
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committer | Austin Clements <austin@google.com> | 2020-11-13 15:15:15 +0000 |
commit | f423d616b15302730c1b737a3b22afca315a7fbe (patch) | |
tree | 3b920dec7950a8e483710eeed9b84d06bcb125a1 | |
parent | 35455fff0ebb7dd1b8e698f245a823ef8c711ac9 (diff) | |
download | go-f423d616b15302730c1b737a3b22afca315a7fbe.tar.gz go-f423d616b15302730c1b737a3b22afca315a7fbe.zip |
cmd/cgo: fix initialization of empty argument types
CL 258938 changed the way C to Go calls work such that they now
construct a C struct on the C side for the arguments and space for the
results. Any pointers in the result space must be zeroed, so we just
zero the whole struct.
However, C makes it surprisingly hard to robustly zero any struct
type. We had used a "{0}" initializer, which works in the vast
majority of cases, but fails if the type is empty or effectively
empty.
This CL fixes this by changing how the cgo tool zero-initializes the
argument struct to be more robust.
Fixes #42495.
Change-Id: Id1749b9d751e59eb7a02a9d44fec0698a2bf63cd
Reviewed-on: https://go-review.googlesource.com/c/go/+/269337
Trust: Austin Clements <austin@google.com>
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
-rw-r--r-- | misc/cgo/test/issue42495.go | 15 | ||||
-rw-r--r-- | src/cmd/cgo/out.go | 10 |
2 files changed, 24 insertions, 1 deletions
diff --git a/misc/cgo/test/issue42495.go b/misc/cgo/test/issue42495.go new file mode 100644 index 0000000000..509a67d9a3 --- /dev/null +++ b/misc/cgo/test/issue42495.go @@ -0,0 +1,15 @@ +// Copyright 2020 The Go Authors. All rights reserved. +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +package cgotest + +// typedef struct { } T42495A; +// typedef struct { int x[0]; } T42495B; +import "C" + +//export Issue42495A +func Issue42495A(C.T42495A) {} + +//export Issue42495B +func Issue42495B(C.T42495B) {} diff --git a/src/cmd/cgo/out.go b/src/cmd/cgo/out.go index 81b28e24e4..bb963799f6 100644 --- a/src/cmd/cgo/out.go +++ b/src/cmd/cgo/out.go @@ -985,7 +985,15 @@ func (p *Package) writeExports(fgo2, fm, fgcc, fgcch io.Writer) { // The results part of the argument structure must be // initialized to 0 so the write barriers generated by // the assignments to these fields in Go are safe. - fmt.Fprintf(fgcc, "\t%s %v _cgo_a = {0};\n", ctype, p.packedAttribute()) + // + // We use a local static variable to get the zeroed + // value of the argument type. This avoids including + // string.h for memset, and is also robust to C++ + // types with constructors. Both GCC and LLVM optimize + // this into just zeroing _cgo_a. + fmt.Fprintf(fgcc, "\ttypedef %s %v _cgo_argtype;\n", ctype, p.packedAttribute()) + fmt.Fprintf(fgcc, "\tstatic _cgo_argtype _cgo_zero;\n") + fmt.Fprintf(fgcc, "\t_cgo_argtype _cgo_a = _cgo_zero;\n") if gccResult != "void" && (len(fntype.Results.List) > 1 || len(fntype.Results.List[0].Names) > 1) { fmt.Fprintf(fgcc, "\t%s r;\n", gccResult) } |