fix: missing backtrace when using std::backtrace::Backtrace on Android

Author: fengys1996

library/Cargo.lock

@@ -42,9 +42,9 @@ checksum = "5c6cb57a04249c6480766f7f7cef5467412af1490f8d1e243141daddada3264f"
 
 [[package]]
 name = "cc"
-version = "1.0.99"
+version = "1.1.10"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "96c51067fd44124faa7f870b4b1c969379ad32b2ba805aa959430ceaa384f695"
+checksum = "e9e8aabfac534be767c909e0690571677d49f41bd8465ae876fe043d52ba5292"
 
 [[package]]
 name = "cfg-if"
@@ -318,6 +318,7 @@ version = "0.0.0"
 dependencies = [
  "addr2line",
  "alloc",
+ "cc",
  "cfg-if",
  "compiler_builtins",
  "core",

library/std/Cargo.toml

@@ -147,3 +147,6 @@ check-cfg = [
     # of declared features, we therefor expect any feature cfg
     'cfg(feature, values(any()))',
 ]
+
+[build-dependencies]
+cc = { version = "1.1.10" }

library/std/build.rs

@@ -1,4 +1,5 @@
 use std::env;
+use std::path::Path;
 
 fn main() {
     println!("cargo:rerun-if-changed=build.rs");
@@ -20,7 +21,6 @@ fn main() {
 
     println!("cargo:rustc-check-cfg=cfg(restricted_std)");
     if target_os == "linux"
-        || target_os == "android"
         || target_os == "netbsd"
         || target_os == "dragonfly"
         || target_os == "openbsd"
@@ -58,6 +58,9 @@ fn main() {
         || env::var("RUSTC_BOOTSTRAP_SYNTHETIC_TARGET").is_ok()
     {
         // These platforms don't have any special requirements.
+    } else if target_os == "android" {
+        // If ANDROID_API >= 21, enable `dl_iterate_phdr` feature.
+        build_android();
     } else {
         // This is for Cargo's build-std support, to mark std as unstable for
         // typically no_std platforms.
@@ -183,3 +186,45 @@ fn main() {
         println!("cargo:rustc-cfg=reliable_f128_math");
     }
 }
+
+fn build_android() {
+    // Used to detect the value of the `__ANDROID_API__`
+    // builtin #define
+    const MARKER: &str = "BACKTRACE_RS_ANDROID_APIVERSION";
+    const ANDROID_API_C: &str = "
+BACKTRACE_RS_ANDROID_APIVERSION __ANDROID_API__
+";
+
+    // Create `android-api.c` on demand.
+    let out_dir = env::var_os("OUT_DIR").unwrap();
+    let android_api_c = Path::new(&out_dir).join("android-api.c");
+    std::fs::write(&android_api_c, ANDROID_API_C).unwrap();
+
+    let expansion = match cc::Build::new().file(&android_api_c).try_expand() {
+        Ok(result) => result,
+        Err(e) => {
+            eprintln!("warning: android version detection failed while running C compiler: {e}");
+            return;
+        }
+    };
+    let expansion = match std::str::from_utf8(&expansion) {
+        Ok(s) => s,
+        Err(_) => return,
+    };
+    eprintln!("expanded android version detection:\n{expansion}");
+    let i = match expansion.find(MARKER) {
+        Some(i) => i,
+        None => return,
+    };
+    let version = match expansion[i + MARKER.len() + 1..].split_whitespace().next() {
+        Some(s) => s,
+        None => return,
+    };
+    let version = match version.parse::<u32>() {
+        Ok(n) => n,
+        Err(_) => return,
+    };
+    if version >= 21 {
+        println!("cargo:rustc-cfg=feature=\"dl_iterate_phdr\"");
+    }
+}