internal/platform: add a function to report whether default builds are PIE

This consolidates a condition that was previously repeated (in
different approximations) in several different places in the code.

For #58807.

Change-Id: Idd308759f6262b1f5c61f79022965612319edf94
Reviewed-on: https://go-review.googlesource.com/c/go/+/475457
Run-TryBot: Bryan Mills <[email protected]>
Auto-Submit: Bryan Mills <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Cherry Mui <[email protected]>

Author: Bryan C. Mills

src/cmd/go/internal/work/init.go

@@ -229,30 +229,16 @@ func buildModeInit() {
 		}
 		ldBuildmode = "c-shared"
 	case "default":
-		switch cfg.Goos {
-		case "android":
-			codegenArg = "-shared"
-			ldBuildmode = "pie"
-		case "windows":
-			if cfg.BuildRace {
-				ldBuildmode = "exe"
+		ldBuildmode = "exe"
+		if platform.DefaultPIE(cfg.Goos, cfg.Goarch) {
+			if cfg.Goos == "windows" && cfg.BuildRace {
+				// PIE is not supported with -race on windows; see https://go.dev/cl/416174.
 			} else {
 				ldBuildmode = "pie"
+				if cfg.Goos != "windows" && !gccgo {
+					codegenArg = "-shared"
+				}
 			}
-		case "ios":
-			codegenArg = "-shared"
-			ldBuildmode = "pie"
-		case "darwin":
-			switch cfg.Goarch {
-			case "arm64":
-				codegenArg = "-shared"
-			}
-			fallthrough
-		default:
-			ldBuildmode = "exe"
-		}
-		if gccgo {
-			codegenArg = ""
 		}
 	case "exe":
 		pkgsFilter = pkgsMain

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

@@ -8,6 +8,7 @@ import (
 	"debug/dwarf"
 	"debug/pe"
 	"fmt"
+	"internal/platform"
 	"internal/testenv"
 	"io"
 	"os"
@@ -891,12 +892,6 @@ func TestRuntimeTypeAttrInternal(t *testing.T) {
 		t.Skip("skipping on plan9; no DWARF symbol table in executables")
 	}
 
-	// TODO(#58807): factor this condition out into a function in
-	// internal/platform so that it won't get out of sync with cmd/link.
-	if runtime.GOOS == "android" || runtime.GOOS == "windows" {
-		t.Skipf("skipping on %s; test is incompatible with relocatable binaries", runtime.GOOS)
-	}
-
 	testRuntimeTypeAttr(t, "-ldflags=-linkmode=internal")
 }
 
@@ -914,10 +909,6 @@ func TestRuntimeTypeAttrExternal(t *testing.T) {
 		t.Skip("-linkmode=external not supported on ppc64")
 	}
 
-	if runtime.GOOS == "windows" {
-		t.Skip("skipping on windows; test is incompatible with relocatable binaries")
-	}
-
 	testRuntimeTypeAttr(t, "-ldflags=-linkmode=external")
 }
 
@@ -985,9 +976,7 @@ func main() {
 		t.Fatalf("*main.X DIE had no runtime type attr. DIE: %v", dies[0])
 	}
 
-	// TODO(#58807): factor this condition out into a function in
-	// internal/platform so that it won't get out of sync with cmd/link.
-	if (runtime.GOOS == "darwin" && runtime.GOARCH == "arm64") || runtime.GOOS == "android" {
+	if platform.DefaultPIE(runtime.GOOS, runtime.GOARCH) {
 		return // everything is PIE, addresses are relocated
 	}
 	if rtAttr.(uint64)+types.Addr != addr {

src/cmd/nm/nm_test.go

@@ -6,6 +6,7 @@ package main
 
 import (
 	"internal/obscuretestdata"
+	"internal/platform"
 	"internal/testenv"
 	"os"
 	"path/filepath"
@@ -165,20 +166,10 @@ func testGoExec(t *testing.T, iscgo, isexternallinker bool) {
 				return true
 			}
 		}
-		// Code is always relocated if the default buildmode is PIE.
-		//
-		// TODO(#58807): factor this condition out into a function in
-		// internal/platform so that it won't get out of sync with cmd/go and
-		// cmd/link.
-		if runtime.GOOS == "android" {
+		if platform.DefaultPIE(runtime.GOOS, runtime.GOARCH) {
+			// Code is always relocated if the default buildmode is PIE.
 			return true
 		}
-		if runtime.GOOS == "windows" {
-			return true
-		}
-		if runtime.GOOS == "darwin" && runtime.GOARCH == "arm64" {
-			return true // On darwin/arm64 everything is PIE
-		}
 		return false
 	}
 

src/cmd/pprof/pprof_test.go

@@ -74,12 +74,10 @@ func mustHaveDisasm(t *testing.T) {
 		t.Skipf("skipping on %s, issue 15255", runtime.GOARCH)
 	}
 
-	// Skip PIE platforms, pprof can't disassemble PIE.
-	//
-	// TODO(#58807): factor this condition out into a function in
-	// internal/platform so that it won't get out of sync with cmd/go and
-	// cmd/link.
-	if (runtime.GOOS == "darwin" && runtime.GOARCH == "arm64") || runtime.GOOS == "android" {
+	// pprof can only disassemble PIE on some platforms.
+	// Skip the ones it can't handle yet.
+	if (runtime.GOOS == "darwin" && runtime.GOARCH == "arm64") ||
+		(runtime.GOOS == "android" && runtime.GOARCH == "arm") {
 		t.Skipf("skipping on %s/%s, issue 46639", runtime.GOOS, runtime.GOARCH)
 	}
 }

src/internal/platform/supported.go

@@ -217,3 +217,17 @@ func InternalLinkPIESupported(goos, goarch string) bool {
 	}
 	return false
 }
+
+// DefaultPIE reports whether goos/goarch produces a PIE binary when using the
+// "default" buildmode.
+func DefaultPIE(goos, goarch string) bool {
+	switch goos {
+	case "android", "ios":
+		return true
+	case "windows":
+		return true // but switches back to "exe" if -race is enabled
+	case "darwin":
+		return goarch == "arm64"
+	}
+	return false
+}