Depend on glibc 2.17 and use getauxval unconditionally.

Author: sunfishcode

README.md

@@ -160,6 +160,14 @@ oldest Linux version supported by:
 The specifics of this policy may change in the future, but we intend it to
 always reflect “very old” Linux versions.
 
+## Minimum glibc Version
+
+On glibc platforms, rustix requires at least glibc 2.17. This is at most the
+oldest glibc version supported by:
+ - [any current Rust target]
+The specifics of this policy may change in the future, but we intend it to
+always reflect “very old” glibc versions.
+
 [MSRV]: #minimum-supported-rust-version-msrv
 [Rust 1.63]: https://blog.rust-lang.org/2022/08/11/Rust-1.63.0.html
 [any current Rust target]: https://doc.rust-lang.org/nightly/rustc/platform-support.html

src/backend/libc/param/auxv.rs

@@ -5,12 +5,9 @@ use crate::backend::c;
 ))]
 use crate::ffi::CStr;
 
-// `getauxval` wasn't supported in glibc until 2.16.
-#[cfg(any(
-    all(target_os = "android", target_pointer_width = "64"),
-    target_os = "linux",
-))]
-weak!(fn getauxval(c::c_ulong) -> *mut c::c_void);
+extern "C" {
+    fn getauxval(type_: c::c_ulong) -> *mut c::c_void;
+}
 
 #[inline]
 pub(crate) fn page_size() -> usize {
@@ -29,14 +26,10 @@ pub(crate) fn clock_ticks_per_second() -> u64 {
 ))]
 #[inline]
 pub(crate) fn linux_hwcap() -> (usize, usize) {
-    if let Some(libc_getauxval) = getauxval.get() {
-        unsafe {
-            let hwcap = libc_getauxval(c::AT_HWCAP) as usize;
-            let hwcap2 = libc_getauxval(c::AT_HWCAP2) as usize;
-            (hwcap, hwcap2)
-        }
-    } else {
-        (0, 0)
+    unsafe {
+        let hwcap = getauxval(c::AT_HWCAP) as usize;
+        let hwcap2 = getauxval(c::AT_HWCAP2) as usize;
+        (hwcap, hwcap2)
     }
 }
 
@@ -61,9 +54,5 @@ pub(crate) fn linux_minsigstksz() -> usize {
 ))]
 #[inline]
 pub(crate) fn linux_execfn() -> &'static CStr {
-    if let Some(libc_getauxval) = getauxval.get() {
-        unsafe { CStr::from_ptr(libc_getauxval(c::AT_EXECFN).cast()) }
-    } else {
-        cstr!("")
-    }
+    unsafe { CStr::from_ptr(getauxval(c::AT_EXECFN).cast()) }
 }

src/backend/linux_raw/param/auxv.rs

@@ -224,7 +224,7 @@ pub(crate) fn vsyscall() -> *const c::c_void {
 
     if vsyscall.is_null() {
         #[cold]
-        fn compute_vsyscall() -> *const c::c_void {
+        fn compute_vsyscall() -> *mut c::c_void {
             init_auxv();
             VSYSCALL.load(Relaxed)
         }
@@ -253,7 +253,7 @@ static PHNUM: AtomicUsize = AtomicUsize::new(0);
 static ENTRY: AtomicUsize = AtomicUsize::new(0);
 #[cfg(feature = "runtime")]
 static RANDOM: AtomicPtr<[u8; 16]> = AtomicPtr::new(null_mut());
-#[cfg(feature = "x86")]
+#[cfg(target_arch = "x86")]
 static VSYSCALL: AtomicPtr<c::c_void> = AtomicPtr::new(null_mut());
 
 const PR_GET_AUXV: c::c_int = 0x4155_5856;

src/backend/linux_raw/param/libc_auxv.rs

@@ -17,14 +17,6 @@ use {
     core::sync::atomic::Ordering::Relaxed,
 };
 
-// `getauxval` wasn't supported in glibc until 2.16. Also this lets us use
-// `*mut` as the return type to preserve strict provenance.
-#[cfg(not(feature = "runtime"))]
-weak!(fn getauxval(c::c_ulong) -> *mut c::c_void);
-
-// With the "runtime" feature, go ahead and depend on `getauxval` existing so
-// that we never fail.
-#[cfg(feature = "runtime")]
 extern "C" {
     fn getauxval(type_: c::c_ulong) -> *mut c::c_void;
 }
@@ -99,18 +91,6 @@ pub(crate) fn clock_ticks_per_second() -> u64 {
 #[cfg(feature = "param")]
 #[inline]
 pub(crate) fn linux_hwcap() -> (usize, usize) {
-    #[cfg(not(feature = "runtime"))]
-    unsafe {
-        if let Some(libc_getauxval) = getauxval.get() {
-            let hwcap = libc_getauxval(AT_HWCAP) as usize;
-            let hwcap2 = libc_getauxval(AT_HWCAP2) as usize;
-            (hwcap, hwcap2)
-        } else {
-            (0, 0)
-        }
-    }
-
-    #[cfg(feature = "runtime")]
     unsafe {
         let hwcap = getauxval(AT_HWCAP) as usize;
         let hwcap2 = getauxval(AT_HWCAP2) as usize;
@@ -140,19 +120,7 @@ pub(crate) fn linux_minsigstksz() -> usize {
 #[cfg(feature = "param")]
 #[inline]
 pub(crate) fn linux_execfn() -> &'static CStr {
-    #[cfg(not(feature = "runtime"))]
-    unsafe {
-        if let Some(libc_getauxval) = getauxval.get() {
-            CStr::from_ptr(libc_getauxval(AT_EXECFN).cast())
-        } else {
-            cstr!("")
-        }
-    }
-
-    #[cfg(feature = "runtime")]
-    unsafe {
-        CStr::from_ptr(getauxval(AT_EXECFN).cast())
-    }
+    unsafe { CStr::from_ptr(getauxval(AT_EXECFN).cast()) }
 }
 
 #[cfg(feature = "runtime")]
@@ -176,19 +144,7 @@ pub(crate) fn exe_phdrs() -> (*const c::c_void, usize, usize) {
 /// if we don't see it, this function returns a null pointer.
 #[inline]
 pub(in super::super) fn sysinfo_ehdr() -> *const Elf_Ehdr {
-    #[cfg(not(feature = "runtime"))]
-    unsafe {
-        if let Some(libc_getauxval) = getauxval.get() {
-            libc_getauxval(AT_SYSINFO_EHDR) as *const Elf_Ehdr
-        } else {
-            null()
-        }
-    }
-
-    #[cfg(feature = "runtime")]
-    unsafe {
-        getauxval(AT_SYSINFO_EHDR) as *const Elf_Ehdr
-    }
+    unsafe { getauxval(AT_SYSINFO_EHDR) as *const Elf_Ehdr }
 }
 
 #[cfg(feature = "runtime")]
@@ -214,7 +170,7 @@ pub(crate) fn vsyscall() -> *const c_void {
     if vsyscall.is_null() {
         #[cold]
         fn compute_vsyscall() -> *mut c_void {
-            let vsyscall = unsafe { getauxval(AT_SYSINFO) } as *mut c_void;
+            let vsyscall = unsafe { getauxval(AT_SYSINFO) as *mut c_void };
             VSYSCALL.store(vsyscall, Relaxed);
             vsyscall
         }

src/lib.rs

@@ -157,15 +157,9 @@ pub(crate) mod check_types;
 #[macro_use]
 pub(crate) mod bitcast;
 
-// linux_raw: Weak symbols are used by the use-libc-auxv feature for
-// glibc 2.15 support.
-//
-// libc: Weak symbols are used to call various functions available in some
-// versions of libc and not others.
-#[cfg(any(
-    all(linux_raw, feature = "use-libc-auxv"),
-    all(libc, not(any(windows, target_os = "espidf", target_os = "wasi")))
-))]
+// Weak symbols are used to call various functions available in some versions
+// of libc and not others.
+#[cfg(all(libc, not(any(windows, target_os = "espidf", target_os = "wasi"))))]
 #[macro_use]
 mod weak;
 

tests/param/auxv.rs

@@ -27,17 +27,17 @@ fn test_clock_ticks_per_second() {
 ))]
 #[test]
 fn test_linux_hwcap() {
-    weak!(fn getauxval(libc::c_ulong) -> libc::c_ulong);
+    extern "C" {
+        fn getauxval(type_: c::c_ulong) -> *mut c::c_void;
+    }
 
-    if let Some(libc_getauxval) = getauxval.get() {
-        let (_hwcap, hwcap2) = linux_hwcap();
+    let (_hwcap, hwcap2) = linux_hwcap();
 
-        // glibc seems to return a different value than `LD_SHOW_AUXV=1` reports.
-        #[cfg(not(target_env = "gnu"))]
-        assert_eq!(_hwcap, unsafe { libc_getauxval(libc::AT_HWCAP) } as usize);
+    // glibc seems to return a different value than `LD_SHOW_AUXV=1` reports.
+    #[cfg(not(target_env = "gnu"))]
+    assert_eq!(_hwcap, unsafe { getauxval(libc::AT_HWCAP) } as usize);
 
-        assert_eq!(hwcap2, unsafe { libc_getauxval(libc::AT_HWCAP2) } as usize);
-    }
+    assert_eq!(hwcap2, unsafe { getauxval(libc::AT_HWCAP2) } as usize);
 }
 
 #[cfg(any(