diff --git a/src/cmd/compile/internal/ppc64/ssa.go b/src/cmd/compile/internal/ppc64/ssa.go index 7e470e55b9..e615f207bd 100644 --- a/src/cmd/compile/internal/ppc64/ssa.go +++ b/src/cmd/compile/internal/ppc64/ssa.go @@ -11,6 +11,7 @@ import ( "cmd/internal/obj" "cmd/internal/obj/ppc64" "math" + "strings" ) // iselOp encodes mapping of comparison operations onto ISEL operands @@ -680,7 +681,42 @@ func ssaGenValue(s *gc.SSAGenState, v *ssa.Value) { p.To.Reg = v.Reg() p.To.Type = obj.TYPE_REG - case ssa.OpPPC64MOVDload, ssa.OpPPC64MOVWload, ssa.OpPPC64MOVHload, ssa.OpPPC64MOVWZload, ssa.OpPPC64MOVBZload, ssa.OpPPC64MOVHZload: + case ssa.OpPPC64MOVDload: + + // MOVDload uses a DS instruction which requires the offset value of the data to be a multiple of 4. + // For offsets known at compile time, a MOVDload won't be selected, but in the case of a go.string, + // the offset is not known until link time. If the load of a go.string uses relocation for the + // offset field of the instruction, and if the offset is not aligned to 4, then a link error will occur. + // To avoid this problem, the full address of the go.string is computed and loaded into the base register, + // and that base register is used for the MOVDload using a 0 offset. This problem can only occur with + // go.string types because other types will have proper alignment. + + gostring := false + switch n := v.Aux.(type) { + case *obj.LSym: + gostring = strings.HasPrefix(n.Name, "go.string.") + } + if gostring { + // Generate full addr of the go.string const + // including AuxInt + p := s.Prog(ppc64.AMOVD) + p.From.Type = obj.TYPE_ADDR + p.From.Reg = v.Args[0].Reg() + gc.AddAux(&p.From, v) + p.To.Type = obj.TYPE_REG + p.To.Reg = v.Reg() + // Load go.string using 0 offset + p = s.Prog(v.Op.Asm()) + p.From.Type = obj.TYPE_MEM + p.From.Reg = v.Reg() + p.To.Type = obj.TYPE_REG + p.To.Reg = v.Reg() + break + } + // Not a go.string, generate a normal load + fallthrough + + case ssa.OpPPC64MOVWload, ssa.OpPPC64MOVHload, ssa.OpPPC64MOVWZload, ssa.OpPPC64MOVBZload, ssa.OpPPC64MOVHZload: p := s.Prog(v.Op.Asm()) p.From.Type = obj.TYPE_MEM p.From.Reg = v.Args[0].Reg() diff --git a/test/fixedbugs/issue24799.go b/test/fixedbugs/issue24799.go new file mode 100644 index 0000000000..c805c86dda --- /dev/null +++ b/test/fixedbugs/issue24799.go @@ -0,0 +1,58 @@ +// run + +// Copyright 2018 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. + +// Loads of 8 byte go.strings cannot use DS relocation +// in case the alignment is not a multiple of 4. + +package main + +import ( + "fmt" +) + +type Level string + +// The following are all go.strings. A link time error can +// occur if an 8 byte load is used to load a go.string that is +// not aligned to 4 bytes due to the type of relocation that +// is generated for the instruction. A fix was made to avoid +// generating an instruction with DS relocation for go.strings +// since their alignment is not known until link time. + +// This problem only affects go.string since other types have +// correct alignment. + +const ( + LevelBad Level = "badvals" + LevelNone Level = "No" + LevelMetadata Level = "Metadata" + LevelRequest Level = "Request" + LevelRequestResponse Level = "RequestResponse" +) + +func ordLevel(l Level) int { + switch l { + case LevelMetadata: + return 1 + case LevelRequest: + return 2 + case LevelRequestResponse: + return 3 + default: + return 0 + } +} + +//go:noinline +func test(l Level) { + if ordLevel(l) < ordLevel(LevelMetadata) { + fmt.Printf("OK\n") + } +} + +func main() { + test(LevelMetadata) +}