Remove std_detect_file_io and std_detect_dlsym_getauxval features

They were introduced back when std_detect was a standalone crate
published to crates.io. The motivation for std_detect_dlsym_getauxval
was to allow using getauxval without dlopen when statically linking
musl, which we now unconditionally do for musl. And for
std_detect_file_io to allow no_std usage, which std_detect now supports
even with that feature enabled as it directly uses libc. This also
prevents accidentally disabling runtime feature detection when using
cargo build -Zbuild-std -Zbuild-std-features=

library/std/Cargo.toml

@@ -128,10 +128,6 @@ debug_refcell = ["core/debug_refcell"]
 
 llvm_enzyme = ["core/llvm_enzyme"]
 
-# Enable std_detect features:
-std_detect_file_io = ["std_detect/std_detect_file_io"]
-std_detect_dlsym_getauxval = ["std_detect/std_detect_dlsym_getauxval"]
-
 # Enable using raw-dylib for Windows imports.
 # This will eventually be the default.
 windows_raw_dylib = ["windows-targets/windows_raw_dylib"]

library/std_detect/Cargo.toml

@@ -25,10 +25,7 @@ core = { version = "1.0.0", package = 'rustc-std-workspace-core' }
 alloc = { version = "1.0.0", package = 'rustc-std-workspace-alloc' }
 
 [target.'cfg(not(windows))'.dependencies]
-libc = { version = "0.2.0", optional = true, default-features = false }
+libc = { version = "0.2.0", default-features = false }
 
 [features]
-default = []
-std_detect_file_io = [ "libc" ]
-std_detect_dlsym_getauxval = [ "libc" ]
-std_detect_env_override = [ "libc" ]
+std_detect_env_override = []

library/std_detect/README.md

@@ -21,32 +21,6 @@ run-time feature detection support than the one offered by Rust's standard
 library. We intend to make `std_detect` more flexible and configurable in this
 regard to better serve the needs of `#[no_std]` targets.
 
-# Features
-
-* `std_detect_dlsym_getauxval` (enabled by default, requires `libc`): Enable to
-use `libc::dlsym` to query whether [`getauxval`] is linked into the binary. When
-this is not the case, this feature allows other fallback methods to perform
-run-time feature detection. When this feature is disabled, `std_detect` assumes
-that [`getauxval`] is linked to the binary. If that is not the case the behavior
-is undefined.
-
-  Note: This feature is ignored on `*-linux-{gnu,musl,ohos}*` and `*-android*` targets
-  because we can safely assume `getauxval` is linked to the binary.
-  * `*-linux-gnu*` targets ([since Rust 1.64](https://blog.rust-lang.org/2022/08/01/Increasing-glibc-kernel-requirements.html))
-    have glibc requirements higher than [glibc 2.16 that added `getauxval`](https://sourceware.org/legacy-ml/libc-announce/2012/msg00000.html).
-  * `*-linux-musl*` targets ([at least since Rust 1.15](https://github.com/rust-lang/rust/blob/1.15.0/src/ci/docker/x86_64-musl/build-musl.sh#L15))
-    use musl newer than [musl 1.1.0 that added `getauxval`](https://git.musl-libc.org/cgit/musl/tree/WHATSNEW?h=v1.1.0#n1197)
-  * `*-linux-ohos*` targets use a [fork of musl 1.2](https://gitee.com/openharmony/docs/blob/master/en/application-dev/reference/native-lib/musl.md)
-  * `*-android*` targets ([since Rust 1.68](https://blog.rust-lang.org/2023/01/09/android-ndk-update-r25.html))
-    have the minimum supported API level higher than [Android 4.3 (API level 18) that added `getauxval`](https://github.com/aosp-mirror/platform_bionic/blob/d3ebc2f7c49a9893b114124d4a6b315f3a328764/libc/include/sys/auxv.h#L49).
-
-* `std_detect_file_io` (enabled by default, requires `std`): Enable to perform run-time feature
-detection using file APIs (e.g. `/proc/self/auxv`, etc.) if other more performant
-methods fail. This feature requires `libstd` as a dependency, preventing the
-crate from working on applications in which `std` is not available.
-
-[`getauxval`]: https://man7.org/linux/man-pages/man3/getauxval.3.html
-
 # Platform support
 
 * All `x86`/`x86_64` targets are supported on all platforms by querying the

library/std_detect/src/detect/mod.rs

@@ -47,21 +47,21 @@
         #[path = "os/x86.rs"]
         mod os;
     }
-    all(any(target_os = "linux", target_os = "android"), feature = "libc") => {
+    any(target_os = "linux", target_os = "android") => {
         #[cfg(any(target_arch = "riscv32", target_arch = "riscv64"))]
         #[path = "os/riscv.rs"]
         mod riscv;
         #[path = "os/linux/mod.rs"]
         mod os;
     }
-    all(target_os = "freebsd", feature = "libc") => {
+    target_os = "freebsd" => {
         #[cfg(target_arch = "aarch64")]
         #[path = "os/aarch64.rs"]
         mod aarch64;
         #[path = "os/freebsd/mod.rs"]
         mod os;
     }
-    all(target_os = "openbsd", feature = "libc") => {
+    target_os = "openbsd" => {
         #[allow(dead_code)] // we don't use code that calls the mrs instruction.
         #[cfg(target_arch = "aarch64")]
         #[path = "os/aarch64.rs"]
@@ -73,7 +73,7 @@
         #[path = "os/windows/aarch64.rs"]
         mod os;
     }
-    all(target_vendor = "apple", target_arch = "aarch64", feature = "libc") => {
+    all(target_vendor = "apple", target_arch = "aarch64") => {
         #[path = "os/darwin/aarch64.rs"]
         mod os;
     }

library/std_detect/src/detect/os/linux/aarch64/tests.rs

@@ -1,6 +1,5 @@
 use super::*;
 
-#[cfg(feature = "std_detect_file_io")]
 mod auxv_from_file {
     use super::auxvec::auxv_from_file;
     use super::*;

library/std_detect/src/detect/os/linux/auxvec.rs

@@ -44,20 +44,16 @@ pub(crate) struct AuxVec {
 ///
 /// There is no perfect way of reading the auxiliary vector.
 ///
-/// - If the `std_detect_dlsym_getauxval` cargo feature is enabled, this will use
-///   `getauxval` if its linked to the binary, and otherwise proceed to a fallback implementation.
-///   When `std_detect_dlsym_getauxval` is disabled, this will assume that `getauxval` is
-///   linked to the binary - if that is not the case the behavior is undefined.
-/// - Otherwise, if the `std_detect_file_io` cargo feature is enabled, it will
+/// - If [`getauxval`] is linked to the binary we use it, and otherwise it will
 ///   try to read `/proc/self/auxv`.
 /// - If that fails, this function returns an error.
 ///
 /// Note that run-time feature detection is not invoked for features that can
 /// be detected at compile-time.
 ///
-///  Note: The `std_detect_dlsym_getauxval` cargo feature is ignored on
-/// `*-linux-{gnu,musl,ohos}*` and `*-android*` targets because we can safely assume `getauxval`
-/// is linked to the binary.
+///  Note: We always directly use `getauxval` on `*-linux-{gnu,musl,ohos}*` and
+/// `*-android*` targets rather than `dlsym` it because we can safely assume
+/// `getauxval` is linked to the binary.
 /// - `*-linux-gnu*` targets ([since Rust 1.64](https://blog.rust-lang.org/2022/08/01/Increasing-glibc-kernel-requirements.html))
 ///   have glibc requirements higher than [glibc 2.16 that added `getauxval`](https://sourceware.org/legacy-ml/libc-announce/2012/msg00000.html).
 /// - `*-linux-musl*` targets ([at least since Rust 1.15](https://github.com/rust-lang/rust/blob/1.15.0/src/ci/docker/x86_64-musl/build-musl.sh#L15))
@@ -71,6 +67,7 @@ pub(crate) struct AuxVec {
 ///
 /// [auxvec_h]: https://github.com/torvalds/linux/blob/master/include/uapi/linux/auxvec.h
 /// [auxv_docs]: https://docs.rs/auxv/0.3.3/auxv/
+/// [`getauxval`]: https://man7.org/linux/man-pages/man3/getauxval.3.html
 pub(crate) fn auxv() -> Result<AuxVec, ()> {
     // Try to call a getauxval function.
     if let Ok(hwcap) = getauxval(AT_HWCAP) {
@@ -115,16 +112,9 @@ pub(crate) fn auxv() -> Result<AuxVec, ()> {
         let _ = hwcap;
     }
 
-    #[cfg(feature = "std_detect_file_io")]
-    {
-        // If calling getauxval fails, try to read the auxiliary vector from
-        // its file:
-        auxv_from_file("/proc/self/auxv").map_err(|_| ())
-    }
-    #[cfg(not(feature = "std_detect_file_io"))]
-    {
-        Err(())
-    }
+    // If calling getauxval fails, try to read the auxiliary vector from
+    // its file:
+    auxv_from_file("/proc/self/auxv").map_err(|_| ())
 }
 
 /// Tries to read the `key` from the auxiliary vector by calling the
@@ -132,14 +122,16 @@ pub(crate) fn auxv() -> Result<AuxVec, ()> {
 fn getauxval(key: usize) -> Result<usize, ()> {
     type F = unsafe extern "C" fn(libc::c_ulong) -> libc::c_ulong;
     cfg_select! {
-        all(
-            feature = "std_detect_dlsym_getauxval",
-            not(all(
+        any(
+            all(
                 target_os = "linux",
                 any(target_env = "gnu", target_env = "musl", target_env = "ohos"),
-            )),
-            not(target_os = "android"),
+            ),
+            target_os = "android",
         ) => {
+            let ffi_getauxval: F = libc::getauxval;
+        }
+        _ => {
             let ffi_getauxval: F = unsafe {
                 let ptr = libc::dlsym(libc::RTLD_DEFAULT, c"getauxval".as_ptr());
                 if ptr.is_null() {
@@ -148,23 +140,18 @@ fn getauxval(key: usize) -> Result<usize, ()> {
                 core::mem::transmute(ptr)
             };
         }
-        _ => {
-            let ffi_getauxval: F = libc::getauxval;
-        }
     }
     Ok(unsafe { ffi_getauxval(key as libc::c_ulong) as usize })
 }
 
 /// Tries to read the auxiliary vector from the `file`. If this fails, this
 /// function returns `Err`.
-#[cfg(feature = "std_detect_file_io")]
 pub(super) fn auxv_from_file(file: &str) -> Result<AuxVec, alloc::string::String> {
     let file = super::read_file(file)?;
     auxv_from_file_bytes(&file)
 }
 
 /// Read auxiliary vector from a slice of bytes.
-#[cfg(feature = "std_detect_file_io")]
 pub(super) fn auxv_from_file_bytes(bytes: &[u8]) -> Result<AuxVec, alloc::string::String> {
     // See <https://github.com/torvalds/linux/blob/v5.15/include/uapi/linux/auxvec.h>.
     //
@@ -181,7 +168,6 @@ pub(super) fn auxv_from_file_bytes(bytes: &[u8]) -> Result<AuxVec, alloc::string
 
 /// Tries to interpret the `buffer` as an auxiliary vector. If that fails, this
 /// function returns `Err`.
-#[cfg(feature = "std_detect_file_io")]
 fn auxv_from_buf(buf: &[usize]) -> Result<AuxVec, alloc::string::String> {
     // Targets with only AT_HWCAP:
     #[cfg(any(

library/std_detect/src/detect/os/linux/auxvec/tests.rs

@@ -41,7 +41,6 @@ fn auxv_dump() {
     }
 }
 
-#[cfg(feature = "std_detect_file_io")]
 cfg_select! {
     target_arch = "arm" => {
         // The tests below can be executed under qemu, where we do not have access to the test
@@ -86,7 +85,6 @@ fn linux_no_hwcap2_aarch64() {
 }
 
 #[test]
-#[cfg(feature = "std_detect_file_io")]
 fn auxv_dump_procfs() {
     if let Ok(auxvec) = auxv_from_file("/proc/self/auxv") {
         println!("{:?}", auxvec);
@@ -103,7 +101,6 @@ fn auxv_dump_procfs() {
     target_arch = "s390x",
 ))]
 #[test]
-#[cfg(feature = "std_detect_file_io")]
 fn auxv_crate_procfs() {
     if let Ok(procfs_auxv) = auxv_from_file("/proc/self/auxv") {
         assert_eq!(auxv().unwrap(), procfs_auxv);

library/std_detect/src/detect/os/linux/mod.rs

@@ -1,11 +1,9 @@
 //! Run-time feature detection on Linux
-//!
-#[cfg(feature = "std_detect_file_io")]
+
 use alloc::vec::Vec;
 
 mod auxvec;
 
-#[cfg(feature = "std_detect_file_io")]
 fn read_file(orig_path: &str) -> Result<Vec<u8>, alloc::string::String> {
     use alloc::format;
 

library/std_detect/src/lib.rs

@@ -27,8 +27,7 @@
 extern crate std;
 
 // rust-lang/rust#83888: removing `extern crate` gives an error that `vec_spare>
-#[cfg_attr(feature = "std_detect_file_io", allow(unused_extern_crates))]
-#[cfg(feature = "std_detect_file_io")]
+#[allow(unused_extern_crates)]
 extern crate alloc;
 
 #[doc(hidden)]

library/sysroot/Cargo.toml

@@ -20,7 +20,7 @@ test = { path = "../test", public = true }
 
 # Forward features to the `std` crate as necessary
 [features]
-default = ["std_detect_file_io", "std_detect_dlsym_getauxval", "panic-unwind"]
+default = ["panic-unwind"]
 backtrace = ["std/backtrace"]
 backtrace-trace-only = ["std/backtrace-trace-only"]
 compiler-builtins-c = ["std/compiler-builtins-c"]
@@ -32,7 +32,5 @@ system-llvm-libunwind = ["std/system-llvm-libunwind"]
 optimize_for_size = ["std/optimize_for_size"]
 panic-unwind = ["std/panic-unwind"]
 profiler = ["dep:profiler_builtins"]
-std_detect_file_io = ["std/std_detect_file_io"]
-std_detect_dlsym_getauxval = ["std/std_detect_dlsym_getauxval"]
 windows_raw_dylib = ["std/windows_raw_dylib"]
 llvm_enzyme = ["std/llvm_enzyme"]