Rollup merge of #133462 - mustartt:aix-improve-bootstrap-loading, r=jieyouxu

Use ReadCache for archive reading in bootstrap

Address expensive archive reading in bootstrap. This fixes https://github.com/rust-lang/rust/issues/133268

Enable the `std` feature of `object` to use `ReadCache` instead of reading the entire archive file into memory to check for headers. This takes minimal extra time to compile compared to introducing other expensive dependencies to `bootstrap`.

r? jieyouxu

compiler/rustc_metadata/src/creader.rs

@@ -1172,7 +1172,7 @@ fn attempt_load_dylib(path: &Path) -> Result<libloading::Library, libloading::Er
         // the expected format is lib<name>.a(libname.so) for the actual
         // dynamic library
         let library_name = path.file_stem().expect("expect a library name");
-        let mut archive_member = OsString::from("a(");
+        let mut archive_member = std::ffi::OsString::from("a(");
         archive_member.push(library_name);
         archive_member.push(".so)");
         let new_path = path.with_extension(archive_member);

src/bootstrap/Cargo.toml

@@ -47,7 +47,7 @@ fd-lock = "4.0"
 home = "0.5"
 ignore = "0.4"
 libc = "0.2"
-object = { version = "0.36.3", default-features = false, features = ["archive", "coff", "read_core", "unaligned"] }
+object = { version = "0.36.3", default-features = false, features = ["archive", "coff", "read_core", "std", "unaligned"] }
 opener = "0.5"
 semver = "1.0"
 serde = "1.0"

src/bootstrap/src/utils/helpers.rs

@@ -61,18 +61,18 @@ pub fn is_dylib(path: &Path) -> bool {
 }
 
 fn is_aix_shared_archive(path: &Path) -> bool {
-    // FIXME(#133268): reading the entire file as &[u8] into memory seems excessive
-    // look into either mmap it or use the ReadCache
-    let data = match fs::read(path) {
-        Ok(data) => data,
-        Err(_) => return false,
-    };
-    let file = match ArchiveFile::parse(&*data) {
+    let file = match fs::File::open(path) {
         Ok(file) => file,
         Err(_) => return false,
     };
+    let reader = object::ReadCache::new(file);
+    let archive = match ArchiveFile::parse(&reader) {
+        Ok(result) => result,
+        Err(_) => return false,
+    };
 
-    file.members()
+    archive
+        .members()
         .filter_map(Result::ok)
         .any(|entry| String::from_utf8_lossy(entry.name()).contains(".so"))
 }