add tests

Author: nrvnrvn

src/cmd/link/doc.go

@@ -48,7 +48,7 @@ Flags:
 	-aslr
 		Enable ASLR for buildmode=c-shared on windows (default true).
 	-bindnow
-		Mark ELF object for immediate function binding (default false).
+		Mark a dynamically linked ELF object for immediate function binding (default false).
 	-buildid id
 		Record id as Go toolchain build id.
 	-buildmode mode

src/cmd/link/internal/ld/elf.go

@@ -1056,17 +1056,17 @@ func elfdynhash(ctxt *Link) {
 	}
 
 	s = ldr.CreateSymForUpdate(".dynamic", 0)
+
+	var dtFlags1 elf.DynFlag1
 	if *flagBindNow {
+		dtFlags1 |= elf.DF_1_NOW
 		Elfwritedynent(ctxt.Arch, s, elf.DT_FLAGS, uint64(elf.DF_BIND_NOW))
 	}
-	switch {
-	case ctxt.BuildMode == BuildModePIE && *flagBindNow:
-		Elfwritedynent(ctxt.Arch, s, elf.DT_FLAGS_1, uint64(elf.DF_1_PIE)|uint64(elf.DF_1_NOW))
-	case ctxt.BuildMode == BuildModePIE && !*flagBindNow:
-		Elfwritedynent(ctxt.Arch, s, elf.DT_FLAGS_1, uint64(elf.DF_1_PIE))
-	case ctxt.BuildMode != BuildModePIE && *flagBindNow:
-		Elfwritedynent(ctxt.Arch, s, elf.DT_FLAGS_1, uint64(elf.DF_1_NOW))
+	if ctxt.BuildMode == BuildModePIE {
+		dtFlags1 |= elf.DF_1_PIE
 	}
+	Elfwritedynent(ctxt.Arch, s, elf.DT_FLAGS_1, uint64(dtFlags1))
+
 	elfverneed = nfile
 	if elfverneed != 0 {
 		elfWriteDynEntSym(ctxt, s, elf.DT_VERNEED, gnuVersionR.Sym())

src/cmd/link/internal/ld/elf_test.go

@@ -8,6 +8,7 @@ package ld
 
 import (
 	"debug/elf"
+	"fmt"
 	"internal/testenv"
 	"os"
 	"path/filepath"
@@ -182,3 +183,108 @@ func main() {
 		}
 	}
 }
+
+func TestElfBindNow(t *testing.T) {
+	t.Parallel()
+	testenv.MustHaveGoBuild(t)
+	testenv.MustInternalLink(t, false)
+
+	const prog = `package main; import _ "net"; func main() {}`
+
+	tests := []struct {
+		name          string
+		args          []string
+		wantDf1Now    bool
+		wantDf1Pie    bool
+		wantDfBindNow bool
+	}{
+		{name: "default"},
+		{
+			name:       "pie",
+			args:       []string{"-buildmode=pie"},
+			wantDf1Pie: true,
+		},
+		{
+			name:          "bindnow",
+			args:          []string{"-ldflags", "-bindnow"},
+			wantDf1Now:    true,
+			wantDfBindNow: true,
+		},
+		{
+			name:          "bindnow-pie",
+			args:          []string{"-buildmode=pie", "-ldflags", "-bindnow"},
+			wantDf1Now:    true,
+			wantDf1Pie:    true,
+			wantDfBindNow: true,
+		},
+	}
+
+	gotDynFlag := func(flags []uint64, dynFlag uint64) bool {
+		for _, flag := range flags {
+			if gotFlag := dynFlag&flag != 0; gotFlag {
+				return true
+			}
+		}
+
+		return false
+	}
+
+	for _, test := range tests {
+		t.Run(
+			test.name, func(t *testing.T) {
+				var (
+					gotDfBindNow, gotDf1Now, gotDf1Pie bool
+
+					dir     = t.TempDir()
+					src     = filepath.Join(dir, fmt.Sprintf("elf_%s.go", test.name))
+					binFile = filepath.Join(dir, test.name)
+				)
+
+				if err := os.WriteFile(src, []byte(prog), 0666); err != nil {
+					t.Fatal(err)
+				}
+
+				cmdArgs := append([]string{"build", "-o", binFile}, append(test.args, src)...)
+				cmd := testenv.Command(t, testenv.GoToolPath(t), cmdArgs...)
+
+				if out, err := cmd.CombinedOutput(); err != nil {
+					t.Fatalf("%v: %v:\n%s", cmd.Args, err, out)
+				}
+
+				fi, err := os.Open(binFile)
+				if err != nil {
+					t.Fatalf("failed to open built file: %v", err)
+				}
+				defer fi.Close()
+
+				elfFile, err := elf.NewFile(fi)
+				if err != nil {
+					t.Skip("The system may not support ELF, skipped.")
+				}
+				defer elfFile.Close()
+
+				flags, err := elfFile.DynValue(elf.DT_FLAGS)
+				if err != nil {
+					t.Fatalf("failed to get DT_FLAGS: %v", err)
+				}
+
+				flags1, err := elfFile.DynValue(elf.DT_FLAGS_1)
+				if err != nil {
+					t.Fatalf("failed to get DT_FLAGS_1: %v", err)
+				}
+
+				if gotDfBindNow = gotDynFlag(flags, uint64(elf.DF_BIND_NOW)); gotDfBindNow != test.wantDfBindNow {
+					t.Fatalf("DT_FLAGS BIND_NOW flag is %v, want: %v", gotDfBindNow, test.wantDfBindNow)
+				}
+
+				if gotDf1Now = gotDynFlag(flags1, uint64(elf.DF_1_NOW)); gotDf1Now != test.wantDf1Now {
+					t.Fatalf("DT_FLAGS_1 DF_1_NOW flag is %v, want: %v", gotDf1Now, test.wantDf1Now)
+				}
+
+				if gotDf1Pie = gotDynFlag(flags1, uint64(elf.DF_1_PIE)); gotDf1Pie != test.wantDf1Pie {
+					t.Fatalf("DT_FLAGS_1 DF_1_PIE flag is %v, want: %v", gotDf1Pie, test.wantDf1Pie)
+				}
+			},
+		)
+	}
+}

src/cmd/link/internal/ld/lib.go

@@ -1600,7 +1600,9 @@ func (ctxt *Link) hostlink() {
 
 	var altLinker string
 	if ctxt.IsELF && (ctxt.DynlinkingGo() || *flagBindNow) {
-		// We force all symbol resolution to be done at program startup
+		// For ELF targets, when producing dynamically linked Go code
+		// or when immediate binding is explicitly requested,
+		// we force all symbol resolution to be done at program startup
 		// because lazy PLT resolution can use large amounts of stack at
 		// times we cannot allow it to do so.
 		argv = append(argv, "-Wl,-z,now")

src/cmd/link/internal/ld/main.go

@@ -63,7 +63,7 @@ func init() {
 // Flags used by the linker. The exported flags are used by the architecture-specific packages.
 var (
 	flagBuildid = flag.String("buildid", "", "record `id` as Go toolchain build id")
-	flagBindNow = flag.Bool("bindnow", false, "mark ELF object for immediate function binding")
+	flagBindNow = flag.Bool("bindnow", false, "mark a dynamically linked ELF object for immediate function binding")
 
 	flagOutfile    = flag.String("o", "", "write output to `file`")
 	flagPluginPath = flag.String("pluginpath", "", "full path name for plugin")