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https://github.com/golang/go
synced 2024-11-17 08:54:41 -07:00
fbdaa96563
The old code ignored the field alignment, and only looked at the field offset: if the field offset required padding, cgo added padding. But while that approach works for Go (at least with the gc toolchain) it doesn't work for C code using packed structs. With a packed struct the added padding may leave the struct at a misaligned position, and the inserted alignment, which cgo is not considering, may introduce additional, unexpected, padding. Padding that ignores alignment is not a good idea when the struct is not packed, and Go structs are never packed. So don't ignore alignment. Fixes #28896 Change-Id: Ie50ea15fa6dc35557497097be9fecfecb11efd8a Reviewed-on: https://go-review.googlesource.com/c/150602 Run-TryBot: Ian Lance Taylor <iant@golang.org> Reviewed-by: Bryan C. Mills <bcmills@google.com>
84 lines
1.4 KiB
Go
84 lines
1.4 KiB
Go
// Copyright 2018 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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// cgo was incorrectly adding padding after a packed struct.
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package cgotest
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/*
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#include <stddef.h>
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#include <stdint.h>
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#include <stdlib.h>
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typedef struct {
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void *f1;
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uint32_t f2;
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} __attribute__((__packed__)) innerPacked;
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typedef struct {
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innerPacked g1;
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uint64_t g2;
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} outerPacked;
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typedef struct {
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void *f1;
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uint32_t f2;
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} innerUnpacked;
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typedef struct {
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innerUnpacked g1;
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uint64_t g2;
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} outerUnpacked;
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size_t offset(int x) {
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switch (x) {
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case 0:
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return offsetof(innerPacked, f2);
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case 1:
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return offsetof(outerPacked, g2);
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case 2:
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return offsetof(innerUnpacked, f2);
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case 3:
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return offsetof(outerUnpacked, g2);
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default:
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abort();
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}
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}
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*/
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import "C"
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import (
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"testing"
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"unsafe"
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)
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func offset(i int) uintptr {
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var pi C.innerPacked
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var po C.outerPacked
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var ui C.innerUnpacked
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var uo C.outerUnpacked
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switch i {
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case 0:
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return unsafe.Offsetof(pi.f2)
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case 1:
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return unsafe.Offsetof(po.g2)
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case 2:
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return unsafe.Offsetof(ui.f2)
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case 3:
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return unsafe.Offsetof(uo.g2)
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default:
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panic("can't happen")
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}
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}
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func test28896(t *testing.T) {
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for i := 0; i < 4; i++ {
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c := uintptr(C.offset(C.int(i)))
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g := offset(i)
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if c != g {
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t.Errorf("%d: C: %d != Go %d", i, c, g)
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}
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}
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}
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