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Due to some recent optimizations related to the compare instruction, DS-form load instructions started to be used to load 8-byte go.strings. This can cause link time errors if the go.string is not aligned to 4 bytes. For DS-form instructions, the value in the offset field must be a multiple of 4. If the offset is known at the time the rules are processed, a DS-form load will not be chosen. But for go.strings, the offset is not known at that time, but a relocation is generated indicating that the linker should fill in the DS relocation. When the linker tries to fill in the relocation, if the offset is not aligned properly, a link error will occur. To fix this, when loading a go.string using MOVDload, the full address of the go.string is generated and loaded into the base register. Then the go.string is loaded with a 0 offset field. Added a testcase that reproduces this problem. Fixes #24799 Change-Id: I6a154e8e1cba64eae290be0fbcb608b75884ecdd Reviewed-on: https://go-review.googlesource.com/107855 Run-TryBot: Lynn Boger <laboger@linux.vnet.ibm.com> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: David Chase <drchase@google.com>
59 lines
1.4 KiB
Go
59 lines
1.4 KiB
Go
// run
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// 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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// Loads of 8 byte go.strings cannot use DS relocation
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// in case the alignment is not a multiple of 4.
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package main
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import (
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"fmt"
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)
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type Level string
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// The following are all go.strings. A link time error can
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// occur if an 8 byte load is used to load a go.string that is
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// not aligned to 4 bytes due to the type of relocation that
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// is generated for the instruction. A fix was made to avoid
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// generating an instruction with DS relocation for go.strings
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// since their alignment is not known until link time.
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// This problem only affects go.string since other types have
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// correct alignment.
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const (
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LevelBad Level = "badvals"
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LevelNone Level = "No"
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LevelMetadata Level = "Metadata"
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LevelRequest Level = "Request"
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LevelRequestResponse Level = "RequestResponse"
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)
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func ordLevel(l Level) int {
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switch l {
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case LevelMetadata:
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return 1
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case LevelRequest:
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return 2
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case LevelRequestResponse:
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return 3
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default:
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return 0
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}
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}
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//go:noinline
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func test(l Level) {
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if ordLevel(l) < ordLevel(LevelMetadata) {
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fmt.Printf("OK\n")
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}
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}
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func main() {
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test(LevelMetadata)
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}
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