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cmd/cgo: use preprocessor macros to avoid prolog redefinitions

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Avoid redefinition errors when a Go file uses a cgo comment to
There is no particularly good reason to do this, but there is also no
particularly good reason that it should fail.

Fixes #27019

Change-Id: Icd6f8197a89be4ee6b03ddae675667998a8b4189
Reviewed-on: https://go-review.googlesource.com/c/152079
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
This commit is contained in:
Ian Lance Taylor 2018-11-30 14:21:33 -08:00
parent c042fedbc8
commit f70bd91435
6 changed files with 130 additions and 1 deletions
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23
src/cmd/cgo/out.go
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@ -1555,6 +1555,7 @@ const builtinProlog = `
/* Define intgo when compiling with GCC. */
typedef ptrdiff_t intgo;
#define GO_CGO_GOSTRING_TYPEDEF
typedef struct { const char *p; intgo n; } _GoString_;
typedef struct { char *p; intgo n; intgo c; } _GoBytes_;
_GoString_ GoString(char *p);
@ -1806,15 +1807,20 @@ void localCgoCheckResult(Eface val) {
// because _cgo_export.h defines GoString as a struct while builtinProlog
// defines it as a function. We don't change this to avoid unnecessarily
// breaking existing code.
// The test of GO_CGO_GOSTRING_TYPEDEF avoids a duplicate definition
// error if a Go file with a cgo comment #include's the export header
// generated by a different package.
const builtinExportProlog = `
#line 1 "cgo-builtin-prolog"
#line 1 "cgo-builtin-export-prolog"
#include <stddef.h> /* for ptrdiff_t below */
#ifndef GO_CGO_EXPORT_PROLOGUE_H
#define GO_CGO_EXPORT_PROLOGUE_H
#ifndef GO_CGO_GOSTRING_TYPEDEF
typedef struct { const char *p; ptrdiff_t n; } _GoString_;
#endif
#endif
`
@ -1823,6 +1829,19 @@ func (p *Package) gccExportHeaderProlog() string {
return strings.Replace(gccExportHeaderProlog, "GOINTBITS", fmt.Sprint(8*p.IntSize), -1)
}
// gccExportHeaderProlog is written to the exported header, after the
// import "C" comment preamble but before the generated declarations
// of exported functions. This permits the generated declarations to
// use the type names that appear in goTypes, above.
//
// The test of GO_CGO_GOSTRING_TYPEDEF avoids a duplicate definition
// error if a Go file with a cgo comment #include's the export header
// generated by a different package. Unfortunately GoString means two
// different things: in this prolog it means a C name for the Go type,
// while in the prolog written into the start of the C code generated
// from a cgo-using Go file it means the C.GoString function. There is
// no way to resolve this conflict, but it also doesn't make much
// difference, as Go code never wants to refer to the latter meaning.
const gccExportHeaderProlog = `
/* Start of boilerplate cgo prologue. */
#line 1 "cgo-gcc-export-header-prolog"
@ -1852,7 +1871,9 @@ typedef double _Complex GoComplex128;
*/
typedef char _check_for_GOINTBITS_bit_pointer_matching_GoInt[sizeof(void*)==GOINTBITS/8 ? 1:-1];
#ifndef GO_CGO_GOSTRING_TYPEDEF
typedef _GoString_ GoString;
#endif
typedef void *GoMap;
typedef void *GoChan;
typedef struct { void *t; void *v; } GoInterface;