diff options
Diffstat (limited to 'src/cmd')
| -rw-r--r-- | src/cmd/compile/internal/base/flag.go | 1 | ||||
| -rw-r--r-- | src/cmd/compile/internal/liveness/plive.go | 165 | ||||
| -rw-r--r-- | src/cmd/compile/internal/test/clobberdead_test.go | 47 |
3 files changed, 210 insertions, 3 deletions
diff --git a/src/cmd/compile/internal/base/flag.go b/src/cmd/compile/internal/base/flag.go index ade17fc0cd..1087f97d07 100644 --- a/src/cmd/compile/internal/base/flag.go +++ b/src/cmd/compile/internal/base/flag.go @@ -90,6 +90,7 @@ type CmdFlags struct { BuildID string "help:\"record `id` as the build id in the export metadata\"" CPUProfile string "help:\"write cpu profile to `file`\"" Complete bool "help:\"compiling complete package (no C or assembly)\"" + ClobberDead bool "help:\"clobber dead stack slots (for debugging)\"" Dwarf bool "help:\"generate DWARF symbols\"" DwarfBASEntries *bool "help:\"use base address selection entries in DWARF\"" // &Ctxt.UseBASEntries, set below DwarfLocationLists *bool "help:\"add location lists to DWARF in optimized mode\"" // &Ctxt.Flag_locationlists, set below diff --git a/src/cmd/compile/internal/liveness/plive.go b/src/cmd/compile/internal/liveness/plive.go index f3fbb8b9b1..c09a8401f7 100644 --- a/src/cmd/compile/internal/liveness/plive.go +++ b/src/cmd/compile/internal/liveness/plive.go @@ -16,7 +16,9 @@ package liveness import ( "crypto/md5" + "crypto/sha1" "fmt" + "os" "sort" "strings" @@ -30,6 +32,7 @@ import ( "cmd/compile/internal/types" "cmd/internal/obj" "cmd/internal/objabi" + "cmd/internal/src" ) // OpVarDef is an annotation for the liveness analysis, marking a place @@ -123,9 +126,9 @@ type liveness struct { unsafePoints bitvec.BitVec // An array with a bit vector for each safe point in the - // current Block during Liveness.epilogue. Indexed in Value + // current Block during liveness.epilogue. Indexed in Value // order for that block. Additionally, for the entry block - // livevars[0] is the entry bitmap. Liveness.compact moves + // livevars[0] is the entry bitmap. liveness.compact moves // these to stackMaps. livevars []bitvec.BitVec @@ -136,6 +139,8 @@ type liveness struct { stackMaps []bitvec.BitVec cache progeffectscache + + doClobber bool // Whether to clobber dead stack slots in this function. } // Map maps from *ssa.Value to LivenessIndex. @@ -387,6 +392,9 @@ func newliveness(fn *ir.Func, f *ssa.Func, vars []*ir.Name, idx map[*ir.Name]int lv.livenessMap.reset() lv.markUnsafePoints() + + lv.enableClobber() + return lv } @@ -820,6 +828,10 @@ func (lv *liveness) epilogue() { live.Or(*live, liveout) } + if lv.doClobber { + lv.clobber(b) + } + // The liveness maps for this block are now complete. Compact them. lv.compact(b) } @@ -873,7 +885,7 @@ func (lv *liveness) compact(b *ssa.Block) { } for _, v := range b.Values { hasStackMap := lv.hasStackMap(v) - isUnsafePoint := lv.allUnsafe || lv.unsafePoints.Get(int32(v.ID)) + isUnsafePoint := lv.allUnsafe || v.Op != ssa.OpClobber && lv.unsafePoints.Get(int32(v.ID)) idx := objw.LivenessIndex{StackMapIndex: objw.StackMapDontCare, IsUnsafePoint: isUnsafePoint} if hasStackMap { idx.StackMapIndex = lv.stackMapSet.add(lv.livevars[pos]) @@ -888,6 +900,153 @@ func (lv *liveness) compact(b *ssa.Block) { lv.livevars = lv.livevars[:0] } +func (lv *liveness) enableClobber() { + // The clobberdead experiment inserts code to clobber pointer slots in all + // the dead variables (locals and args) at every synchronous safepoint. + if !base.Flag.ClobberDead { + return + } + if lv.fn.Pragma&ir.CgoUnsafeArgs != 0 { + // C or assembly code uses the exact frame layout. Don't clobber. + return + } + if len(lv.vars) > 10000 || len(lv.f.Blocks) > 10000 { + // Be careful to avoid doing too much work. + // Bail if >10000 variables or >10000 blocks. + // Otherwise, giant functions make this experiment generate too much code. + return + } + if lv.f.Name == "forkAndExecInChild" || lv.f.Name == "wbBufFlush" { + // forkAndExecInChild calls vfork on some platforms. + // The code we add here clobbers parts of the stack in the child. + // When the parent resumes, it is using the same stack frame. But the + // child has clobbered stack variables that the parent needs. Boom! + // In particular, the sys argument gets clobbered. + // + // runtime.wbBufFlush must not modify its arguments. See the comments + // in runtime/mwbbuf.go:wbBufFlush. + return + } + if h := os.Getenv("GOCLOBBERDEADHASH"); h != "" { + // Clobber only functions where the hash of the function name matches a pattern. + // Useful for binary searching for a miscompiled function. + hstr := "" + for _, b := range sha1.Sum([]byte(lv.f.Name)) { + hstr += fmt.Sprintf("%08b", b) + } + if !strings.HasSuffix(hstr, h) { + return + } + fmt.Printf("\t\t\tCLOBBERDEAD %s\n", lv.f.Name) + } + lv.doClobber = true +} + +// Inserts code to clobber pointer slots in all the dead variables (locals and args) +// at every synchronous safepoint in b. +func (lv *liveness) clobber(b *ssa.Block) { + // Copy block's values to a temporary. + oldSched := append([]*ssa.Value{}, b.Values...) + b.Values = b.Values[:0] + idx := 0 + + // Clobber pointer slots in all dead variables at entry. + if b == lv.f.Entry { + for len(oldSched) > 0 && len(oldSched[0].Args) == 0 { + // Skip argless ops. We need to skip at least + // the lowered ClosurePtr op, because it + // really wants to be first. This will also + // skip ops like InitMem and SP, which are ok. + b.Values = append(b.Values, oldSched[0]) + oldSched = oldSched[1:] + } + clobber(lv, b, lv.livevars[0]) + idx++ + } + + // Copy values into schedule, adding clobbering around safepoints. + for _, v := range oldSched { + if !lv.hasStackMap(v) { + b.Values = append(b.Values, v) + continue + } + clobber(lv, b, lv.livevars[idx]) + b.Values = append(b.Values, v) + idx++ + } +} + +// clobber generates code to clobber pointer slots in all dead variables +// (those not marked in live). Clobbering instructions are added to the end +// of b.Values. +func clobber(lv *liveness, b *ssa.Block, live bitvec.BitVec) { + for i, n := range lv.vars { + if !live.Get(int32(i)) && !n.Addrtaken() { + // Don't clobber stack objects (address-taken). They are + // tracked dynamically. + clobberVar(b, n) + } + } +} + +// clobberVar generates code to trash the pointers in v. +// Clobbering instructions are added to the end of b.Values. +func clobberVar(b *ssa.Block, v *ir.Name) { + clobberWalk(b, v, 0, v.Type()) +} + +// b = block to which we append instructions +// v = variable +// offset = offset of (sub-portion of) variable to clobber (in bytes) +// t = type of sub-portion of v. +func clobberWalk(b *ssa.Block, v *ir.Name, offset int64, t *types.Type) { + if !t.HasPointers() { + return + } + switch t.Kind() { + case types.TPTR, + types.TUNSAFEPTR, + types.TFUNC, + types.TCHAN, + types.TMAP: + clobberPtr(b, v, offset) + + case types.TSTRING: + // struct { byte *str; int len; } + clobberPtr(b, v, offset) + + case types.TINTER: + // struct { Itab *tab; void *data; } + // or, when isnilinter(t)==true: + // struct { Type *type; void *data; } + clobberPtr(b, v, offset) + clobberPtr(b, v, offset+int64(types.PtrSize)) + + case types.TSLICE: + // struct { byte *array; int len; int cap; } + clobberPtr(b, v, offset) + + case types.TARRAY: + for i := int64(0); i < t.NumElem(); i++ { + clobberWalk(b, v, offset+i*t.Elem().Size(), t.Elem()) + } + + case types.TSTRUCT: + for _, t1 := range t.Fields().Slice() { + clobberWalk(b, v, offset+t1.Offset, t1.Type) + } + + default: + base.Fatalf("clobberWalk: unexpected type, %v", t) + } +} + +// clobberPtr generates a clobber of the pointer at offset offset in v. +// The clobber instruction is added at the end of b. +func clobberPtr(b *ssa.Block, v *ir.Name, offset int64) { + b.NewValue0IA(src.NoXPos, ssa.OpClobber, types.TypeVoid, offset, v) +} + func (lv *liveness) showlive(v *ssa.Value, live bitvec.BitVec) { if base.Flag.Live == 0 || ir.FuncName(lv.fn) == "init" || strings.HasPrefix(ir.FuncName(lv.fn), ".") { return diff --git a/src/cmd/compile/internal/test/clobberdead_test.go b/src/cmd/compile/internal/test/clobberdead_test.go new file mode 100644 index 0000000000..3e2aadcbf5 --- /dev/null +++ b/src/cmd/compile/internal/test/clobberdead_test.go @@ -0,0 +1,47 @@ +// Copyright 2021 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 test + +import ( + "internal/testenv" + "io/ioutil" + "os/exec" + "path/filepath" + "testing" +) + +const helloSrc = ` +package main +import "fmt" +func main() { fmt.Println("hello") } +` + +func TestClobberDead(t *testing.T) { + // Test that clobberdead mode generates correct program. + + if testing.Short() { + // This test rebuilds the runtime with a special flag, which + // takes a while. + t.Skip("skip in short mode") + } + testenv.MustHaveGoRun(t) + t.Parallel() + + tmpdir := t.TempDir() + src := filepath.Join(tmpdir, "x.go") + err := ioutil.WriteFile(src, []byte(helloSrc), 0644) + if err != nil { + t.Fatalf("write file failed: %v", err) + } + + cmd := exec.Command(testenv.GoToolPath(t), "run", "-gcflags=all=-clobberdead", src) + out, err := cmd.CombinedOutput() + if err != nil { + t.Fatalf("go run failed: %v\n%s", err, out) + } + if string(out) != "hello\n" { + t.Errorf("wrong output: got %q, want %q", out, "hello\n") + } +} |