soong: Add crt_pad_segment to .so's

crt_pad_segment adds a NOTE to the ELF which is used by the binoic
loader to determine whether it should pad segments when mapping them
into the virtual address space, such that there are no gaps between
mappings of consecutive segments. This avoids an increase in
unreclaimable kernel slab memory usage for VMAs on devices where the
runtime-page-size > elf-segment-p_align.

Since -fandroid-pad-segment [1] respects -nostdlib used in android
platform builds, soong must link in crt_pad_segment to platform shared
libraries.

For simplicity, link crt_pad_segment everywhere that crtend_so is
applicable, ignoring nocrt property, as there is no other reason
to track these separately.

Example:

❯ readelf -WS /system/lib64/libc++.so [Output simplified]

...
Section Headers:
  [Nr] Name              Type            Address          Off    Size   ES Flg Lk Inf Al
...
  [ 2] .note.android.pad_segment NOTE            0000000000000288 000288 000018 00   A  0   0  4
...

[1] https://github.com/llvm/llvm-project/pull/77244

Bug: 316403210
Test: readelf -WS <lib>.so
Change-Id: Icc06611376cfd5ee4de7281b4134f9f8ffe7ca60
Signed-off-by: Kalesh Singh <kaleshsingh@google.com>

apex/apex_test.go

@@ -1455,6 +1455,7 @@ func TestRuntimeApexShouldInstallHwasanIfLibcDependsOnIt(t *testing.T) {
 			name: "libc",
 			no_libcrt: true,
 			nocrt: true,
+			no_crt_pad_segment: true,
 			stl: "none",
 			system_shared_libs: [],
 			stubs: { versions: ["1"] },
@@ -1469,6 +1470,7 @@ func TestRuntimeApexShouldInstallHwasanIfLibcDependsOnIt(t *testing.T) {
 			name: "libclang_rt.hwasan",
 			no_libcrt: true,
 			nocrt: true,
+			no_crt_pad_segment: true,
 			stl: "none",
 			system_shared_libs: [],
 			srcs: [""],
@@ -1511,6 +1513,7 @@ func TestRuntimeApexShouldInstallHwasanIfHwaddressSanitized(t *testing.T) {
 			name: "libc",
 			no_libcrt: true,
 			nocrt: true,
+			no_crt_pad_segment: true,
 			stl: "none",
 			system_shared_libs: [],
 			stubs: { versions: ["1"] },
@@ -1521,6 +1524,7 @@ func TestRuntimeApexShouldInstallHwasanIfHwaddressSanitized(t *testing.T) {
 			name: "libclang_rt.hwasan",
 			no_libcrt: true,
 			nocrt: true,
+			no_crt_pad_segment: true,
 			stl: "none",
 			system_shared_libs: [],
 			srcs: [""],

cc/config/bionic.go

@@ -24,6 +24,7 @@ var (
 	bionicCrtBeginStaticBinary, bionicCrtEndStaticBinary   = []string{"crtbegin_static"}, []string{"crtend_android"}
 	bionicCrtBeginSharedBinary, bionicCrtEndSharedBinary   = []string{"crtbegin_dynamic"}, []string{"crtend_android"}
 	bionicCrtBeginSharedLibrary, bionicCrtEndSharedLibrary = []string{"crtbegin_so"}, []string{"crtend_so"}
+	bionicCrtPadSegmentSharedLibrary                       = []string{"crt_pad_segment"}
 )
 
 func (toolchainBionic) Bionic() bool { return true }
@@ -36,9 +37,10 @@ func (toolchainBionic) ExecutableSuffix() string { return "" }
 
 func (toolchainBionic) AvailableLibraries() []string { return nil }
 
-func (toolchainBionic) CrtBeginStaticBinary() []string  { return bionicCrtBeginStaticBinary }
+func (toolchainBionic) CrtBeginStaticBinary() []string       { return bionicCrtBeginStaticBinary }
-func (toolchainBionic) CrtBeginSharedBinary() []string  { return bionicCrtBeginSharedBinary }
+func (toolchainBionic) CrtBeginSharedBinary() []string       { return bionicCrtBeginSharedBinary }
-func (toolchainBionic) CrtBeginSharedLibrary() []string { return bionicCrtBeginSharedLibrary }
+func (toolchainBionic) CrtBeginSharedLibrary() []string      { return bionicCrtBeginSharedLibrary }
-func (toolchainBionic) CrtEndStaticBinary() []string    { return bionicCrtEndStaticBinary }
+func (toolchainBionic) CrtEndStaticBinary() []string         { return bionicCrtEndStaticBinary }
-func (toolchainBionic) CrtEndSharedBinary() []string    { return bionicCrtEndSharedBinary }
+func (toolchainBionic) CrtEndSharedBinary() []string         { return bionicCrtEndSharedBinary }
-func (toolchainBionic) CrtEndSharedLibrary() []string   { return bionicCrtEndSharedLibrary }
+func (toolchainBionic) CrtEndSharedLibrary() []string        { return bionicCrtEndSharedLibrary }
+func (toolchainBionic) CrtPadSegmentSharedLibrary() []string { return bionicCrtPadSegmentSharedLibrary }

cc/config/toolchain.go

@@ -100,6 +100,7 @@ type Toolchain interface {
 	CrtEndStaticBinary() []string
 	CrtEndSharedBinary() []string
 	CrtEndSharedLibrary() []string
+	CrtPadSegmentSharedLibrary() []string
 
 	// DefaultSharedLibraries returns the list of shared libraries that will be added to all
 	// targets unless they explicitly specify system_shared_libs.
@@ -155,12 +156,13 @@ func (toolchainBase) LibclangRuntimeLibraryArch() string {
 
 type toolchainNoCrt struct{}
 
-func (toolchainNoCrt) CrtBeginStaticBinary() []string  { return nil }
+func (toolchainNoCrt) CrtBeginStaticBinary() []string       { return nil }
-func (toolchainNoCrt) CrtBeginSharedBinary() []string  { return nil }
+func (toolchainNoCrt) CrtBeginSharedBinary() []string       { return nil }
-func (toolchainNoCrt) CrtBeginSharedLibrary() []string { return nil }
+func (toolchainNoCrt) CrtBeginSharedLibrary() []string      { return nil }
-func (toolchainNoCrt) CrtEndStaticBinary() []string    { return nil }
+func (toolchainNoCrt) CrtEndStaticBinary() []string         { return nil }
-func (toolchainNoCrt) CrtEndSharedBinary() []string    { return nil }
+func (toolchainNoCrt) CrtEndSharedBinary() []string         { return nil }
-func (toolchainNoCrt) CrtEndSharedLibrary() []string   { return nil }
+func (toolchainNoCrt) CrtEndSharedLibrary() []string        { return nil }
+func (toolchainNoCrt) CrtPadSegmentSharedLibrary() []string { return nil }
 
 func (toolchainBase) DefaultSharedLibraries() []string {
 	return nil

cc/config/x86_linux_host.go

@@ -328,12 +328,13 @@ type toolchainMusl struct {
 
 func (toolchainMusl) Musl() bool { return true }
 
-func (toolchainMusl) CrtBeginStaticBinary() []string  { return muslCrtBeginStaticBinary }
+func (toolchainMusl) CrtBeginStaticBinary() []string       { return muslCrtBeginStaticBinary }
-func (toolchainMusl) CrtBeginSharedBinary() []string  { return muslCrtBeginSharedBinary }
+func (toolchainMusl) CrtBeginSharedBinary() []string       { return muslCrtBeginSharedBinary }
-func (toolchainMusl) CrtBeginSharedLibrary() []string { return muslCrtBeginSharedLibrary }
+func (toolchainMusl) CrtBeginSharedLibrary() []string      { return muslCrtBeginSharedLibrary }
-func (toolchainMusl) CrtEndStaticBinary() []string    { return muslCrtEndStaticBinary }
+func (toolchainMusl) CrtEndStaticBinary() []string         { return muslCrtEndStaticBinary }
-func (toolchainMusl) CrtEndSharedBinary() []string    { return muslCrtEndSharedBinary }
+func (toolchainMusl) CrtEndSharedBinary() []string         { return muslCrtEndSharedBinary }
-func (toolchainMusl) CrtEndSharedLibrary() []string   { return muslCrtEndSharedLibrary }
+func (toolchainMusl) CrtEndSharedLibrary() []string        { return muslCrtEndSharedLibrary }
+func (toolchainMusl) CrtPadSegmentSharedLibrary() []string { return nil }
 
 func (toolchainMusl) DefaultSharedLibraries() []string { return MuslDefaultSharedLibraries }
 

cc/library.go

@@ -974,6 +974,10 @@ func (library *libraryDecorator) linkerDeps(ctx DepsContext, deps Deps) Deps {
 		if library.baseLinker.Properties.crt() {
 			deps.CrtBegin = append(deps.CrtBegin, ctx.toolchain().CrtBeginSharedLibrary()...)
 			deps.CrtEnd = append(deps.CrtEnd, ctx.toolchain().CrtEndSharedLibrary()...)
+
+		}
+		if library.baseLinker.Properties.crtPadSegment() {
+			deps.CrtEnd = append(deps.CrtEnd, ctx.toolchain().CrtPadSegmentSharedLibrary()...)
 		}
 		deps.WholeStaticLibs = append(deps.WholeStaticLibs, library.SharedProperties.Shared.Whole_static_libs...)
 		deps.StaticLibs = append(deps.StaticLibs, library.SharedProperties.Shared.Static_libs...)

cc/linker.go

@@ -91,6 +91,10 @@ type BaseLinkerProperties struct {
 	// compiling crt or libc.
 	Nocrt *bool `android:"arch_variant"`
 
+	// don't link in crt_pad_segment. This flag is currently only used internal to
+	// soong for testing and for vndk prebuilt shared libraries.
+	No_crt_pad_segment *bool `android:"arch_variant"`
+
 	// deprecated and ignored because lld makes it unnecessary. See b/189475744.
 	Group_static_libs *bool `android:"arch_variant"`
 
@@ -253,6 +257,10 @@ func (blp *BaseLinkerProperties) libCrt() bool {
 	return blp.No_libcrt == nil || !*blp.No_libcrt
 }
 
+func (blp *BaseLinkerProperties) crtPadSegment() bool {
+	return blp.No_crt_pad_segment == nil || !*blp.No_crt_pad_segment
+}
+
 func NewBaseLinker(sanitize *sanitize) *baseLinker {
 	return &baseLinker{sanitize: sanitize}
 }

cc/testing.go

@@ -77,6 +77,7 @@ func commonDefaultModules() string {
 			no_libcrt: true,
 			sdk_version: "minimum",
 			nocrt: true,
+			no_crt_pad_segment: true,
 			system_shared_libs: [],
 			stl: "none",
 			check_elf_files: false,
@@ -384,6 +385,11 @@ func commonDefaultModules() string {
 			objs: ["crtbrand"],
 		}
 
+		cc_object {
+			name: "crt_pad_segment",
+			defaults: ["crt_defaults"],
+		}
+
 		cc_object {
 			name: "crtbrand",
 			defaults: ["crt_defaults"],

cc/vendor_snapshot_test.go

@@ -341,6 +341,7 @@ func TestVendorSnapshotUse(t *testing.T) {
 		vendor: true,
 		nocrt: true,
 		no_libcrt: true,
+		no_crt_pad_segment: true,
 		stl: "none",
 		system_shared_libs: [],
 		compile_multilib: "64",
@@ -458,6 +459,7 @@ func TestVendorSnapshotUse(t *testing.T) {
 		vendor: true,
 		nocrt: true,
 		no_libcrt: true,
+		no_crt_pad_segment: true,
 		stl: "none",
 		system_shared_libs: [],
 	}
@@ -467,6 +469,7 @@ func TestVendorSnapshotUse(t *testing.T) {
 		vendor: true,
 		nocrt: true,
 		no_libcrt: true,
+		no_crt_pad_segment: true,
 		stl: "none",
 		system_shared_libs: [],
 		shared_libs: ["libvndk", "libvendor_available", "libllndk"],
@@ -487,6 +490,7 @@ func TestVendorSnapshotUse(t *testing.T) {
 		vendor: true,
 		nocrt: true,
 		no_libcrt: true,
+		no_crt_pad_segment: true,
 		stl: "none",
 		system_shared_libs: [],
 		static_libs: ["libvendor"],
@@ -501,6 +505,7 @@ func TestVendorSnapshotUse(t *testing.T) {
 		vendor: true,
 		nocrt: true,
 		no_libcrt: true,
+		no_crt_pad_segment: true,
 		stl: "none",
 		system_shared_libs: [],
 		vndk: {
@@ -597,6 +602,7 @@ func TestVendorSnapshotUse(t *testing.T) {
 		target_arch: "arm64",
 		compile_multilib: "both",
 		vendor: true,
+		no_crt_pad_segment: true,
 		shared_libs: [
 			"libvendor_without_snapshot",
 			"libvendor_available",
@@ -620,6 +626,7 @@ func TestVendorSnapshotUse(t *testing.T) {
 		target_arch: "arm64",
 		compile_multilib: "both",
 		vendor: true,
+		no_crt_pad_segment: true,
 		overrides: ["libvendor"],
 		shared_libs: [
 			"libvendor_without_snapshot",
@@ -657,6 +664,7 @@ func TestVendorSnapshotUse(t *testing.T) {
 		target_arch: "arm64",
 		compile_multilib: "32",
 		vendor: true,
+		no_crt_pad_segment: true,
 		arch: {
 			arm: {
 				src: "lib32.so",
@@ -683,6 +691,7 @@ func TestVendorSnapshotUse(t *testing.T) {
 		target_arch: "arm64",
 		compile_multilib: "64",
 		vendor: true,
+		no_crt_pad_segment: true,
 		arch: {
 			arm64: {
 				src: "lib64.so",
@@ -722,6 +731,7 @@ func TestVendorSnapshotUse(t *testing.T) {
 		target_arch: "arm64",
 		compile_multilib: "both",
 		vendor: true,
+		no_crt_pad_segment: true,
 		arch: {
 			arm64: {
 				src: "libvendor_available.so",

cc/vndk_prebuilt.go

@@ -232,6 +232,7 @@ func vndkPrebuiltSharedLibrary() *Module {
 	prebuilt.properties.Check_elf_files = BoolPtr(false)
 	prebuilt.baseLinker.Properties.No_libcrt = BoolPtr(true)
 	prebuilt.baseLinker.Properties.Nocrt = BoolPtr(true)
+	prebuilt.baseLinker.Properties.No_crt_pad_segment = BoolPtr(true)
 
 	// Prevent default system libs (libc, libm, and libdl) from being linked
 	if prebuilt.baseLinker.Properties.System_shared_libs == nil {

rust/vendor_snapshot_test.go

@@ -553,6 +553,7 @@ func TestVendorSnapshotUse(t *testing.T) {
 		vendor: true,
 		nocrt: true,
 		no_libcrt: true,
+		no_crt_pad_segment: true,
 		stl: "none",
 		system_shared_libs: [],
 	}
@@ -857,6 +858,7 @@ func TestVendorSnapshotUse(t *testing.T) {
 		target_arch: "arm64",
 		compile_multilib: "32",
 		vendor: true,
+		no_crt_pad_segment: true,
 		arch: {
 			arm: {
 				src: "lib32.so",
@@ -870,6 +872,7 @@ func TestVendorSnapshotUse(t *testing.T) {
 		target_arch: "arm64",
 		compile_multilib: "64",
 		vendor: true,
+		no_crt_pad_segment: true,
 		arch: {
 			arm64: {
 				src: "lib64.so",
@@ -882,6 +885,7 @@ func TestVendorSnapshotUse(t *testing.T) {
 		target_arch: "arm64",
 		compile_multilib: "64",
 		vendor: true,
+		no_crt_pad_segment: true,
 		arch: {
 			arm64: {
 				src: "liblog.so",
@@ -913,6 +917,7 @@ func TestVendorSnapshotUse(t *testing.T) {
 		target_arch: "arm64",
 		compile_multilib: "both",
 		vendor: true,
+		no_crt_pad_segment: true,
 		arch: {
 			arm64: {
 				src: "libvendor_available.so",