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>
diff --git a/cc/config/bionic.go b/cc/config/bionic.go
index a1e3851..ed724f5 100644
--- a/cc/config/bionic.go
+++ b/cc/config/bionic.go
@@ -24,6 +24,7 @@
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) AvailableLibraries() []string { return nil }
-func (toolchainBionic) CrtBeginStaticBinary() []string { return bionicCrtBeginStaticBinary }
-func (toolchainBionic) CrtBeginSharedBinary() []string { return bionicCrtBeginSharedBinary }
-func (toolchainBionic) CrtBeginSharedLibrary() []string { return bionicCrtBeginSharedLibrary }
-func (toolchainBionic) CrtEndStaticBinary() []string { return bionicCrtEndStaticBinary }
-func (toolchainBionic) CrtEndSharedBinary() []string { return bionicCrtEndSharedBinary }
-func (toolchainBionic) CrtEndSharedLibrary() []string { return bionicCrtEndSharedLibrary }
+func (toolchainBionic) CrtBeginStaticBinary() []string { return bionicCrtBeginStaticBinary }
+func (toolchainBionic) CrtBeginSharedBinary() []string { return bionicCrtBeginSharedBinary }
+func (toolchainBionic) CrtBeginSharedLibrary() []string { return bionicCrtBeginSharedLibrary }
+func (toolchainBionic) CrtEndStaticBinary() []string { return bionicCrtEndStaticBinary }
+func (toolchainBionic) CrtEndSharedBinary() []string { return bionicCrtEndSharedBinary }
+func (toolchainBionic) CrtEndSharedLibrary() []string { return bionicCrtEndSharedLibrary }
+func (toolchainBionic) CrtPadSegmentSharedLibrary() []string { return bionicCrtPadSegmentSharedLibrary }
diff --git a/cc/config/toolchain.go b/cc/config/toolchain.go
index 62f75d1..71e98fe 100644
--- a/cc/config/toolchain.go
+++ b/cc/config/toolchain.go
@@ -100,6 +100,7 @@
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 @@
type toolchainNoCrt struct{}
-func (toolchainNoCrt) CrtBeginStaticBinary() []string { return nil }
-func (toolchainNoCrt) CrtBeginSharedBinary() []string { return nil }
-func (toolchainNoCrt) CrtBeginSharedLibrary() []string { return nil }
-func (toolchainNoCrt) CrtEndStaticBinary() []string { return nil }
-func (toolchainNoCrt) CrtEndSharedBinary() []string { return nil }
-func (toolchainNoCrt) CrtEndSharedLibrary() []string { return nil }
+func (toolchainNoCrt) CrtBeginStaticBinary() []string { return nil }
+func (toolchainNoCrt) CrtBeginSharedBinary() []string { return nil }
+func (toolchainNoCrt) CrtBeginSharedLibrary() []string { return nil }
+func (toolchainNoCrt) CrtEndStaticBinary() []string { return nil }
+func (toolchainNoCrt) CrtEndSharedBinary() []string { return nil }
+func (toolchainNoCrt) CrtEndSharedLibrary() []string { return nil }
+func (toolchainNoCrt) CrtPadSegmentSharedLibrary() []string { return nil }
func (toolchainBase) DefaultSharedLibraries() []string {
return nil
diff --git a/cc/config/x86_linux_host.go b/cc/config/x86_linux_host.go
index f95da0b..f497bf9 100644
--- a/cc/config/x86_linux_host.go
+++ b/cc/config/x86_linux_host.go
@@ -328,12 +328,13 @@
func (toolchainMusl) Musl() bool { return true }
-func (toolchainMusl) CrtBeginStaticBinary() []string { return muslCrtBeginStaticBinary }
-func (toolchainMusl) CrtBeginSharedBinary() []string { return muslCrtBeginSharedBinary }
-func (toolchainMusl) CrtBeginSharedLibrary() []string { return muslCrtBeginSharedLibrary }
-func (toolchainMusl) CrtEndStaticBinary() []string { return muslCrtEndStaticBinary }
-func (toolchainMusl) CrtEndSharedBinary() []string { return muslCrtEndSharedBinary }
-func (toolchainMusl) CrtEndSharedLibrary() []string { return muslCrtEndSharedLibrary }
+func (toolchainMusl) CrtBeginStaticBinary() []string { return muslCrtBeginStaticBinary }
+func (toolchainMusl) CrtBeginSharedBinary() []string { return muslCrtBeginSharedBinary }
+func (toolchainMusl) CrtBeginSharedLibrary() []string { return muslCrtBeginSharedLibrary }
+func (toolchainMusl) CrtEndStaticBinary() []string { return muslCrtEndStaticBinary }
+func (toolchainMusl) CrtEndSharedBinary() []string { return muslCrtEndSharedBinary }
+func (toolchainMusl) CrtEndSharedLibrary() []string { return muslCrtEndSharedLibrary }
+func (toolchainMusl) CrtPadSegmentSharedLibrary() []string { return nil }
func (toolchainMusl) DefaultSharedLibraries() []string { return MuslDefaultSharedLibraries }
diff --git a/cc/library.go b/cc/library.go
index 4b6ac59..d091261 100644
--- a/cc/library.go
+++ b/cc/library.go
@@ -974,6 +974,10 @@
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...)
diff --git a/cc/linker.go b/cc/linker.go
index 85c128e..2c50db2 100644
--- a/cc/linker.go
+++ b/cc/linker.go
@@ -91,6 +91,10 @@
// 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 @@
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}
}
diff --git a/cc/testing.go b/cc/testing.go
index bac41e7..9c2900c 100644
--- a/cc/testing.go
+++ b/cc/testing.go
@@ -77,6 +77,7 @@
no_libcrt: true,
sdk_version: "minimum",
nocrt: true,
+ no_crt_pad_segment: true,
system_shared_libs: [],
stl: "none",
check_elf_files: false,
@@ -385,6 +386,11 @@
}
cc_object {
+ name: "crt_pad_segment",
+ defaults: ["crt_defaults"],
+ }
+
+ cc_object {
name: "crtbrand",
defaults: ["crt_defaults"],
srcs: ["crtbrand.c"],
diff --git a/cc/vendor_snapshot_test.go b/cc/vendor_snapshot_test.go
index 890a533..0a55431 100644
--- a/cc/vendor_snapshot_test.go
+++ b/cc/vendor_snapshot_test.go
@@ -341,6 +341,7 @@
vendor: true,
nocrt: true,
no_libcrt: true,
+ no_crt_pad_segment: true,
stl: "none",
system_shared_libs: [],
compile_multilib: "64",
@@ -458,6 +459,7 @@
vendor: true,
nocrt: true,
no_libcrt: true,
+ no_crt_pad_segment: true,
stl: "none",
system_shared_libs: [],
}
@@ -467,6 +469,7 @@
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 @@
vendor: true,
nocrt: true,
no_libcrt: true,
+ no_crt_pad_segment: true,
stl: "none",
system_shared_libs: [],
static_libs: ["libvendor"],
@@ -501,6 +505,7 @@
vendor: true,
nocrt: true,
no_libcrt: true,
+ no_crt_pad_segment: true,
stl: "none",
system_shared_libs: [],
vndk: {
@@ -597,6 +602,7 @@
target_arch: "arm64",
compile_multilib: "both",
vendor: true,
+ no_crt_pad_segment: true,
shared_libs: [
"libvendor_without_snapshot",
"libvendor_available",
@@ -620,6 +626,7 @@
target_arch: "arm64",
compile_multilib: "both",
vendor: true,
+ no_crt_pad_segment: true,
overrides: ["libvendor"],
shared_libs: [
"libvendor_without_snapshot",
@@ -657,6 +664,7 @@
target_arch: "arm64",
compile_multilib: "32",
vendor: true,
+ no_crt_pad_segment: true,
arch: {
arm: {
src: "lib32.so",
@@ -683,6 +691,7 @@
target_arch: "arm64",
compile_multilib: "64",
vendor: true,
+ no_crt_pad_segment: true,
arch: {
arm64: {
src: "lib64.so",
@@ -722,6 +731,7 @@
target_arch: "arm64",
compile_multilib: "both",
vendor: true,
+ no_crt_pad_segment: true,
arch: {
arm64: {
src: "libvendor_available.so",
diff --git a/cc/vndk_prebuilt.go b/cc/vndk_prebuilt.go
index eb1790f..62870b8 100644
--- a/cc/vndk_prebuilt.go
+++ b/cc/vndk_prebuilt.go
@@ -232,6 +232,7 @@
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 {