android: use jemalloc on Android (#32273)

This is a fix for the crash issue in 64-bit ARM [#32175][1].

When targeting Android 11 and above, 64-bit ARM platforms
have the 'Tagged Pointer' feature enabled by default which
causes memory allocated using the system allocator to have
a non-zero 'tag' set in the highest byte of heap addresses.

This is incompatible with SpiderMonkey which assumes that
only the bottom 48 bits are set and asserts this at various
points.

Both Servo and Gecko have a similar architecture where
the pointer to a heap allocated DOM struct is encoded as
a JS::Value and stored in the DOM_OBJECT_SLOT (reserved
slot) of the JSObject which reflects the native DOM struct.

As observed in #32175, even Gecko crashes with `jemalloc`
disabled which suggests that support for using the native
system allocator with tagged pointers enabled by default
is not present at the moment.

[1]: #32175

Signed-off-by: Mukilan Thiyagarajan <mukilan@igalia.com>

components/allocator/Cargo.toml

@@ -12,13 +12,13 @@ path = "lib.rs"
 [features]
 use-system-allocator = ["libc"]
 
-[target.'cfg(not(any(windows, target_os = "android",  target_env = "ohos")))'.dependencies]
+[target.'cfg(not(any(windows, target_env = "ohos")))'.dependencies]
 jemallocator = { workspace = true }
 jemalloc-sys = { workspace = true }
 libc = { workspace = true, optional = true }
 
 [target.'cfg(windows)'.dependencies]
 winapi = { workspace = true, features = ["heapapi"] }
 
-[target.'cfg(any(target_os = "android", target_env = "ohos"))'.dependencies]
+[target.'cfg(target_env = "ohos")'.dependencies]
 libc = { workspace = true }

components/allocator/lib.rs

@@ -9,12 +9,7 @@ static ALLOC: Allocator = Allocator;
 
 pub use crate::platform::*;
 
-#[cfg(not(any(
-    windows,
-    target_os = "android",
-    feature = "use-system-allocator",
-    target_env = "ohos"
-)))]
+#[cfg(not(any(windows, feature = "use-system-allocator", target_env = "ohos")))]
 mod platform {
     use std::os::raw::c_void;
 
@@ -37,11 +32,7 @@ mod platform {
 
 #[cfg(all(
     not(windows),
-    any(
-        target_os = "android",
-        feature = "use-system-allocator",
-        target_env = "ohos"
-    )
+    any(feature = "use-system-allocator", target_env = "ohos")
 ))]
 mod platform {
     pub use std::alloc::System as Allocator;

components/profile/Cargo.toml

@@ -23,7 +23,7 @@ task_info = { path = "../../support/rust-task_info" }
 [target.'cfg(target_os = "linux")'.dependencies]
 regex = { workspace = true }
 
-[target.'cfg(not(any(target_os = "windows", target_os = "android")))'.dependencies]
+[target.'cfg(not(target_os = "windows"))'.dependencies]
 libc = { workspace = true }
-[target.'cfg(not(any(target_os = "windows", target_os = "android", target_env = "ohos")))'.dependencies]
+[target.'cfg(not(any(target_os = "windows", target_env = "ohos")))'.dependencies]
 jemalloc-sys = { workspace = true }

components/profile/mem.rs

@@ -387,16 +387,16 @@ impl ReportsForest {
 //---------------------------------------------------------------------------
 
 mod system_reporter {
-    #[cfg(not(any(target_os = "windows", target_os = "android", target_env = "ohos")))]
+    #[cfg(not(any(target_os = "windows", target_env = "ohos")))]
     use std::ffi::CString;
-    #[cfg(not(any(target_os = "windows", target_os = "android", target_env = "ohos")))]
+    #[cfg(not(any(target_os = "windows", target_env = "ohos")))]
     use std::mem::size_of;
-    #[cfg(not(any(target_os = "windows", target_os = "android", target_env = "ohos")))]
+    #[cfg(not(any(target_os = "windows", target_env = "ohos")))]
     use std::ptr::null_mut;
 
     #[cfg(target_os = "linux")]
     use libc::c_int;
-    #[cfg(not(any(target_os = "windows", target_os = "android", target_env = "ohos")))]
+    #[cfg(not(any(target_os = "windows", target_env = "ohos")))]
     use libc::{c_void, size_t};
     use profile_traits::mem::{Report, ReportKind, ReporterRequest};
     use profile_traits::path;
@@ -499,10 +499,10 @@ mod system_reporter {
         None
     }
 
-    #[cfg(not(any(target_os = "windows", target_os = "android", target_env = "ohos")))]
+    #[cfg(not(any(target_os = "windows", target_env = "ohos")))]
     use jemalloc_sys::mallctl;
 
-    #[cfg(not(any(target_os = "windows", target_os = "android", target_env = "ohos")))]
+    #[cfg(not(any(target_os = "windows", target_env = "ohos")))]
     fn jemalloc_stat(value_name: &str) -> Option<usize> {
         // Before we request the measurement of interest, we first send an "epoch"
         // request. Without that jemalloc gives cached statistics(!) which can be
@@ -549,7 +549,7 @@ mod system_reporter {
         Some(value as usize)
     }
 
-    #[cfg(any(target_os = "windows", target_os = "android", target_env = "ohos"))]
+    #[cfg(any(target_os = "windows", target_env = "ohos"))]
     fn jemalloc_stat(_value_name: &str) -> Option<usize> {
         None
     }

ports/jniapi/build.rs

@@ -4,6 +4,7 @@
 
 use std::env;
 use std::fs::File;
+use std::io::Write;
 use std::path::PathBuf;
 
 use gl_generator::{Api, Fallbacks, Profile, Registry};
@@ -35,6 +36,16 @@ fn main() {
         println!("cargo:rustc-link-lib=EGL");
     }
 
+    // FIXME: We need this workaround since jemalloc-sys still links
+    // to libgcc instead of libunwind, but Android NDK 23c and above
+    // don't have libgcc. We can't disable jemalloc for Android as
+    // in 64-bit aarch builds, the system allocator uses tagged
+    // pointers by default which causes the assertions in SM & mozjs
+    // to fail. See https://github.com/servo/servo/issues/32175.
+    let mut libgcc = File::create(dest.join("libgcc.a")).unwrap();
+    libgcc.write_all(b"INPUT(-lunwind)").unwrap();
+    println!("cargo:rustc-link-search=native={}", dest.display());
+
     let mut default_prefs = PathBuf::from(env!("CARGO_MANIFEST_DIR"));
     default_prefs.push("../../resources/prefs.json");
     let prefs: Value = serde_json::from_reader(File::open(&default_prefs).unwrap()).unwrap();