Strip libgcc to only keep fallback symbols

We use libgcc as fallback for symbols not present in libclang_rt
builtins, however we didn't know what exact symbols were being used,
some may not be intended to fallback.

Create libgcc_stripped, which only contains unwind symbols from libgcc.

Bug: 29275768
Test: bionic-unit-tests
Change-Id: I98df02ead7f6cca4e76ec92d4f880de4e03f5b5c
Merged-In: I5b349fa6138e51663bf3b67109b880b4356da8e8
(cherry picked from commit acee27cd72)

cc/builder.go

@@ -255,6 +255,7 @@ type builderFlags struct {
 	groupStaticLibs bool
 
 	stripKeepSymbols       bool
+	stripKeepSymbolsList   string
 	stripKeepMiniDebugInfo bool
 	stripAddGnuDebuglink   bool
 	stripUseGnuStrip       bool
@@ -823,6 +824,9 @@ func TransformStrip(ctx android.ModuleContext, inputFile android.Path,
 	if flags.stripKeepSymbols {
 		args += " --keep-symbols"
 	}
+	if flags.stripKeepSymbolsList != "" {
+		args += " -k" + flags.stripKeepSymbolsList
+	}
 	if flags.stripUseGnuStrip {
 		args += " --use-gnu-strip"
 	}

cc/cc_test.go

@@ -1833,13 +1833,13 @@ func TestStaticLibDepExport(t *testing.T) {
 	// Check the shared version of lib2.
 	variant := "android_arm64_armv8-a_core_shared"
 	module := ctx.ModuleForTests("lib2", variant).Module().(*Module)
-	checkStaticLibs(t, []string{"lib1", "libclang_rt.builtins-aarch64-android", "libatomic", "libgcc"}, module)
+	checkStaticLibs(t, []string{"lib1", "libclang_rt.builtins-aarch64-android", "libatomic", "libgcc_stripped"}, module)
 
 	// Check the static version of lib2.
 	variant = "android_arm64_armv8-a_core_static"
 	module = ctx.ModuleForTests("lib2", variant).Module().(*Module)
 	// libc++_static is linked additionally.
-	checkStaticLibs(t, []string{"lib1", "libc++_static", "libclang_rt.builtins-aarch64-android", "libatomic", "libgcc"}, module)
+	checkStaticLibs(t, []string{"lib1", "libc++_static", "libclang_rt.builtins-aarch64-android", "libatomic", "libgcc_stripped"}, module)
 }
 
 var compilerFlagsTestCases = []struct {

cc/linker.go

@@ -228,10 +228,10 @@ func (linker *baseLinker) linkerDeps(ctx DepsContext, deps Deps) Deps {
 		// libclang_rt.builtins, libgcc and libatomic have to be last on the command line
 		if !Bool(linker.Properties.No_libcrt) {
 			deps.LateStaticLibs = append(deps.LateStaticLibs, config.BuiltinsRuntimeLibrary(ctx.toolchain()))
-		}
-
-		deps.LateStaticLibs = append(deps.LateStaticLibs, "libatomic")
-		if !Bool(linker.Properties.No_libgcc) {
+			deps.LateStaticLibs = append(deps.LateStaticLibs, "libatomic")
+			deps.LateStaticLibs = append(deps.LateStaticLibs, "libgcc_stripped")
+		} else if !Bool(linker.Properties.No_libgcc) {
+			deps.LateStaticLibs = append(deps.LateStaticLibs, "libatomic")
 			deps.LateStaticLibs = append(deps.LateStaticLibs, "libgcc")
 		}
 

cc/strip.go

@@ -15,15 +15,19 @@
 package cc
 
 import (
+	"strings"
+
 	"android/soong/android"
 )
 
 type StripProperties struct {
 	Strip struct {
-		None         *bool
-		All          *bool
-		Keep_symbols *bool
-	}
+		None              *bool    `android:"arch_variant"`
+		All               *bool    `android:"arch_variant"`
+		Keep_symbols      *bool    `android:"arch_variant"`
+		Keep_symbols_list []string `android:"arch_variant"`
+		Use_gnu_strip     *bool    `android:"arch_variant"`
+	} `android:"arch_variant"`
 }
 
 type stripper struct {
@@ -42,9 +46,14 @@ func (stripper *stripper) strip(ctx ModuleContext, in android.Path, out android.
 	} else {
 		if Bool(stripper.StripProperties.Strip.Keep_symbols) {
 			flags.stripKeepSymbols = true
+		} else if len(stripper.StripProperties.Strip.Keep_symbols_list) > 0 {
+			flags.stripKeepSymbolsList = strings.Join(stripper.StripProperties.Strip.Keep_symbols_list, ",")
 		} else if !Bool(stripper.StripProperties.Strip.All) {
 			flags.stripKeepMiniDebugInfo = true
 		}
+		if Bool(stripper.StripProperties.Strip.Use_gnu_strip) {
+			flags.stripUseGnuStrip = true
+		}
 		if ctx.Config().Debuggable() && !flags.stripKeepMiniDebugInfo {
 			flags.stripAddGnuDebuglink = true
 		}

cc/testing.go

@@ -69,6 +69,13 @@ func GatherRequiredDepsForTest(os android.OsType) string {
 			src: "",
 		}
 
+		toolchain_library {
+			name: "libgcc_stripped",
+			vendor_available: true,
+			recovery_available: true,
+			src: "",
+		}
+
 		cc_library {
 			name: "libc",
 			no_libgcc: true,

cc/toolchain_library.go

@@ -34,6 +34,8 @@ type toolchainLibraryProperties struct {
 type toolchainLibraryDecorator struct {
 	*libraryDecorator
 
+	stripper
+
 	Properties toolchainLibraryProperties
 }
 
@@ -45,7 +47,7 @@ func (*toolchainLibraryDecorator) linkerDeps(ctx DepsContext, deps Deps) Deps {
 func (library *toolchainLibraryDecorator) linkerProps() []interface{} {
 	var props []interface{}
 	props = append(props, library.libraryDecorator.linkerProps()...)
-	return append(props, &library.Properties)
+	return append(props, &library.Properties, &library.stripper.StripProperties)
 }
 
 func ToolchainLibraryFactory() android.Module {
@@ -75,7 +77,17 @@ func (library *toolchainLibraryDecorator) link(ctx ModuleContext,
 		return android.PathForSource(ctx, "")
 	}
 
-	return android.PathForSource(ctx, *library.Properties.Src)
+	srcPath := android.PathForSource(ctx, *library.Properties.Src)
+
+	if library.stripper.StripProperties.Strip.Keep_symbols_list != nil {
+		fileName := ctx.ModuleName() + staticLibraryExtension
+		outputFile := android.PathForModuleOut(ctx, fileName)
+		buildFlags := flagsToBuilderFlags(flags)
+		library.stripper.strip(ctx, srcPath, outputFile, buildFlags)
+		return outputFile
+	}
+
+	return srcPath
 }
 
 func (library *toolchainLibraryDecorator) nativeCoverage() bool {