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fix: SIGSEGV in getauxval — override broken CRT stub with dlsym wrapper

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compiler-rt's init_have_lse_atomics calls getauxval(AT_HWCAP) at
library load time. The static getauxval from the CRT reads from
__libc_auxv which is NULL in shared libraries → SIGSEGV at 0x0.

Fix: compile getauxval_fix.c that provides a getauxval() which uses
dlsym(RTLD_DEFAULT) to find the real bionic getauxval at runtime.
Also switch to libc++_shared.so (bundled in APK) to avoid pulling
in static libc stubs.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
This commit is contained in:
Claude
2026-04-05 08:39:57 +00:00
parent f6d51fce61
commit 9098e28a1f
4 changed files with 57 additions and 9 deletions
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39
crates/wzp-android/build.rs
View File

@@ -4,6 +4,12 @@ fn main() {
let target = std::env::var("TARGET").unwrap_or_default();
if target.contains("android") {
// Compile a getauxval override FIRST so it takes precedence over the
// broken static stub from compiler-rt/CRT that crashes in shared libs.
cc::Build::new()
.file("cpp/getauxval_fix.c")
.compile("getauxval_fix");
let oboe_dir = fetch_oboe();
match oboe_dir {
Some(oboe_path) => {
@@ -13,7 +19,7 @@ fn main() {
build
.cpp(true)
.std("c++17")
.cpp_link_stdlib(None)
.cpp_link_stdlib(Some("c++_shared"))
.include("cpp")
.include(oboe_path.join("include"))
.include(oboe_path.join("src"))
@@ -31,17 +37,22 @@ fn main() {
cc::Build::new()
.cpp(true)
.std("c++17")
.cpp_link_stdlib(None)
.cpp_link_stdlib(Some("c++_shared"))
.file("cpp/oboe_stub.cpp")
.include("cpp")
.compile("oboe_bridge");
}
}
// Android NDK splits the static C++ runtime into two archives:
// libc++_static.a — STL (containers, strings, algorithms)
// libc++abi.a — ABI (RTTI, exceptions, typeinfo vtables)
// Both are required; cc crate's cpp_link_stdlib only handles the first.
// Use libc++_shared.so (dynamic) instead of static linking.
//
// Static libc++ pulls in getauxval.o from libc.a, which has a
// stub that reads from __libc_auxv (only initialized for executables,
// not shared libs). This causes SIGSEGV when ring/cpufeatures calls
// getauxval at load time. Using the shared library avoids this.
//
// libc++_shared.so must be bundled in the APK alongside libwzp_android.so.
// build.rs copies it to jniLibs/ automatically.
if let Ok(ndk) = std::env::var("ANDROID_NDK_HOME") {
let arch = if target.contains("aarch64") {
"aarch64-linux-android"
@@ -54,9 +65,21 @@ fn main() {
};
let lib_dir = format!("{ndk}/toolchains/llvm/prebuilt/linux-x86_64/sysroot/usr/lib/{arch}");
println!("cargo:rustc-link-search=native={lib_dir}");
// Copy libc++_shared.so next to libwzp_android.so
let shared_so = format!("{lib_dir}/libc++_shared.so");
let shared_path = std::path::Path::new(&shared_so);
if shared_path.exists() {
// Output to the jniLibs directory (one level up from OUT_DIR)
let out_dir = std::env::var("OUT_DIR").unwrap();
// Also copy to a known location that Gradle cargoNdkBuild uses
let jni_dir = format!("{}/../../../jniLibs/arm64-v8a", out_dir);
let _ = std::fs::create_dir_all(&jni_dir);
let _ = std::fs::copy(shared_path, format!("{jni_dir}/libc++_shared.so"));
println!("cargo:warning=Copied libc++_shared.so to jniLibs");
}
}
println!("cargo:rustc-link-lib=static=c++_static");
println!("cargo:rustc-link-lib=static=c++abi");
println!("cargo:rustc-link-lib=c++_shared");
// Oboe needs liblog and libOpenSLES from Android
println!("cargo:rustc-link-lib=log");