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diff --git a/src/tools/rustfmt/tests/target/cfg_if/detect/os/linux/auxvec.rs b/src/tools/rustfmt/tests/target/cfg_if/detect/os/linux/auxvec.rs
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+++ b/src/tools/rustfmt/tests/target/cfg_if/detect/os/linux/auxvec.rs
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+//! Parses ELF auxiliary vectors.
+#![cfg_attr(not(target_arch = "aarch64"), allow(dead_code))]
+
+#[cfg(feature = "std_detect_file_io")]
+use crate::{fs::File, io::Read};
+
+/// Key to access the CPU Hardware capabilities bitfield.
+pub(crate) const AT_HWCAP: usize = 16;
+/// Key to access the CPU Hardware capabilities 2 bitfield.
+#[cfg(any(target_arch = "arm", target_arch = "powerpc64"))]
+pub(crate) const AT_HWCAP2: usize = 26;
+
+/// Cache HWCAP bitfields of the ELF Auxiliary Vector.
+///
+/// If an entry cannot be read all the bits in the bitfield are set to zero.
+/// This should be interpreted as all the features being disabled.
+#[derive(Debug, Copy, Clone)]
+pub(crate) struct AuxVec {
+    pub hwcap: usize,
+    #[cfg(any(target_arch = "arm", target_arch = "powerpc64"))]
+    pub hwcap2: usize,
+}
+
+/// ELF Auxiliary Vector
+///
+/// The auxiliary vector is a memory region in a running ELF program's stack
+/// composed of (key: usize, value: usize) pairs.
+///
+/// The keys used in the aux vector are platform dependent. For Linux, they are
+/// defined in [linux/auxvec.h][auxvec_h]. The hardware capabilities of a given
+/// CPU can be queried with the  `AT_HWCAP` and `AT_HWCAP2` keys.
+///
+/// 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
+///   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. Also note that if this function returns an
+/// error, cpuinfo still can (and will) be used to try to perform run-time
+/// feature detecton on some platforms.
+///
+/// For more information about when `getauxval` is available check the great
+/// [`auxv` crate documentation][auxv_docs].
+///
+/// [auxvec_h]: https://github.com/torvalds/linux/blob/master/include/uapi/linux/auxvec.h
+/// [auxv_docs]: https://docs.rs/auxv/0.3.3/auxv/
+pub(crate) fn auxv() -> Result<AuxVec, ()> {
+    #[cfg(feature = "std_detect_dlsym_getauxval")]
+    {
+        // Try to call a dynamically-linked getauxval function.
+        if let Ok(hwcap) = getauxval(AT_HWCAP) {
+            // Targets with only AT_HWCAP:
+            #[cfg(any(target_arch = "aarch64", target_arch = "mips", target_arch = "mips64"))]
+            {
+                if hwcap != 0 {
+                    return Ok(AuxVec { hwcap });
+                }
+            }
+
+            // Targets with AT_HWCAP and AT_HWCAP2:
+            #[cfg(any(target_arch = "arm", target_arch = "powerpc64"))]
+            {
+                if let Ok(hwcap2) = getauxval(AT_HWCAP2) {
+                    if hwcap != 0 && hwcap2 != 0 {
+                        return Ok(AuxVec { hwcap, hwcap2 });
+                    }
+                }
+            }
+            drop(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")
+        }
+        #[cfg(not(feature = "std_detect_file_io"))]
+        {
+            Err(())
+        }
+    }
+
+    #[cfg(not(feature = "std_detect_dlsym_getauxval"))]
+    {
+        let hwcap = unsafe { ffi_getauxval(AT_HWCAP) };
+
+        // Targets with only AT_HWCAP:
+        #[cfg(any(target_arch = "aarch64", target_arch = "mips", target_arch = "mips64"))]
+        {
+            if hwcap != 0 {
+                return Ok(AuxVec { hwcap });
+            }
+        }
+
+        // Targets with AT_HWCAP and AT_HWCAP2:
+        #[cfg(any(target_arch = "arm", target_arch = "powerpc64"))]
+        {
+            let hwcap2 = unsafe { ffi_getauxval(AT_HWCAP2) };
+            if hwcap != 0 && hwcap2 != 0 {
+                return Ok(AuxVec { hwcap, hwcap2 });
+            }
+        }
+    }
+}
+
+/// Tries to read the `key` from the auxiliary vector by calling the
+/// dynamically-linked `getauxval` function. If the function is not linked,
+/// this function return `Err`.
+#[cfg(feature = "std_detect_dlsym_getauxval")]
+fn getauxval(key: usize) -> Result<usize, ()> {
+    use libc;
+    pub type F = unsafe extern "C" fn(usize) -> usize;
+    unsafe {
+        let ptr = libc::dlsym(libc::RTLD_DEFAULT, "getauxval\0".as_ptr() as *const _);
+        if ptr.is_null() {
+            return Err(());
+        }
+
+        let ffi_getauxval: F = mem::transmute(ptr);
+        Ok(ffi_getauxval(key))
+    }
+}
+
+/// Tries to read the auxiliary vector from the `file`. If this fails, this
+/// function returns `Err`.
+#[cfg(feature = "std_detect_file_io")]
+fn auxv_from_file(file: &str) -> Result<AuxVec, ()> {
+    let mut file = File::open(file).map_err(|_| ())?;
+
+    // See <https://github.com/torvalds/linux/blob/v3.19/include/uapi/linux/auxvec.h>.
+    //
+    // The auxiliary vector contains at most 32 (key,value) fields: from
+    // `AT_EXECFN = 31` to `AT_NULL = 0`. That is, a buffer of
+    // 2*32 `usize` elements is enough to read the whole vector.
+    let mut buf = [0_usize; 64];
+    {
+        let raw: &mut [u8; 64 * mem::size_of::<usize>()] = unsafe { mem::transmute(&mut buf) };
+        file.read(raw).map_err(|_| ())?;
+    }
+    auxv_from_buf(&buf)
+}
+
+/// 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; 64]) -> Result<AuxVec, ()> {
+    // Targets with only AT_HWCAP:
+    #[cfg(any(target_arch = "aarch64", target_arch = "mips", target_arch = "mips64"))]
+    {
+        for el in buf.chunks(2) {
+            match el[0] {
+                AT_HWCAP => return Ok(AuxVec { hwcap: el[1] }),
+                _ => (),
+            }
+        }
+    }
+    // Targets with AT_HWCAP and AT_HWCAP2:
+    #[cfg(any(target_arch = "arm", target_arch = "powerpc64"))]
+    {
+        let mut hwcap = None;
+        let mut hwcap2 = None;
+        for el in buf.chunks(2) {
+            match el[0] {
+                AT_HWCAP => hwcap = Some(el[1]),
+                AT_HWCAP2 => hwcap2 = Some(el[1]),
+                _ => (),
+            }
+        }
+
+        if let (Some(hwcap), Some(hwcap2)) = (hwcap, hwcap2) {
+            return Ok(AuxVec { hwcap, hwcap2 });
+        }
+    }
+    drop(buf);
+    Err(())
+}
+
+#[cfg(test)]
+mod tests {
+    extern crate auxv as auxv_crate;
+    use super::*;
+
+    // Reads the Auxiliary Vector key from /proc/self/auxv
+    // using the auxv crate.
+    #[cfg(feature = "std_detect_file_io")]
+    fn auxv_crate_getprocfs(key: usize) -> Option<usize> {
+        use self::auxv_crate::procfs::search_procfs_auxv;
+        use self::auxv_crate::AuxvType;
+        let k = key as AuxvType;
+        match search_procfs_auxv(&[k]) {
+            Ok(v) => Some(v[&k] as usize),
+            Err(_) => None,
+        }
+    }
+
+    // Reads the Auxiliary Vector key from getauxval()
+    // using the auxv crate.
+    #[cfg(not(any(target_arch = "mips", target_arch = "mips64")))]
+    fn auxv_crate_getauxval(key: usize) -> Option<usize> {
+        use self::auxv_crate::getauxval::Getauxval;
+        use self::auxv_crate::AuxvType;
+        let q = auxv_crate::getauxval::NativeGetauxval {};
+        match q.getauxval(key as AuxvType) {
+            Ok(v) => Some(v as usize),
+            Err(_) => None,
+        }
+    }
+
+    // FIXME: on mips/mips64 getauxval returns 0, and /proc/self/auxv
+    // does not always contain the AT_HWCAP key under qemu.
+    #[cfg(not(any(target_arch = "mips", target_arch = "mips64", target_arch = "powerpc")))]
+    #[test]
+    fn auxv_crate() {
+        let v = auxv();
+        if let Some(hwcap) = auxv_crate_getauxval(AT_HWCAP) {
+            let rt_hwcap = v.expect("failed to find hwcap key").hwcap;
+            assert_eq!(rt_hwcap, hwcap);
+        }
+
+        // Targets with AT_HWCAP and AT_HWCAP2:
+        #[cfg(any(target_arch = "arm", target_arch = "powerpc64"))]
+        {
+            if let Some(hwcap2) = auxv_crate_getauxval(AT_HWCAP2) {
+                let rt_hwcap2 = v.expect("failed to find hwcap2 key").hwcap2;
+                assert_eq!(rt_hwcap2, hwcap2);
+            }
+        }
+    }
+
+    #[test]
+    fn auxv_dump() {
+        if let Ok(auxvec) = auxv() {
+            println!("{:?}", auxvec);
+        } else {
+            println!("both getauxval() and reading /proc/self/auxv failed!");
+        }
+    }
+
+    #[cfg(feature = "std_detect_file_io")]
+    cfg_if! {
+        if #[cfg(target_arch = "arm")] {
+            #[test]
+            fn linux_rpi3() {
+                let file = concat!(env!("CARGO_MANIFEST_DIR"), "/src/detect/test_data/linux-rpi3.auxv");
+                println!("file: {}", file);
+                let v = auxv_from_file(file).unwrap();
+                assert_eq!(v.hwcap, 4174038);
+                assert_eq!(v.hwcap2, 16);
+            }
+
+            #[test]
+            #[should_panic]
+            fn linux_macos_vb() {
+                let file = concat!(env!("CARGO_MANIFEST_DIR"), "/src/detect/test_data/macos-virtualbox-linux-x86-4850HQ.auxv");
+                println!("file: {}", file);
+                let v = auxv_from_file(file).unwrap();
+                // this file is incomplete (contains hwcap but not hwcap2), we
+                // want to fall back to /proc/cpuinfo in this case, so
+                // reading should fail. assert_eq!(v.hwcap, 126614527);
+                // assert_eq!(v.hwcap2, 0);
+            }
+        } else if #[cfg(target_arch = "aarch64")] {
+            #[test]
+            fn linux_x64() {
+                let file = concat!(env!("CARGO_MANIFEST_DIR"), "/src/detect/test_data/linux-x64-i7-6850k.auxv");
+                println!("file: {}", file);
+                let v = auxv_from_file(file).unwrap();
+                assert_eq!(v.hwcap, 3219913727);
+            }
+        }
+    }
+
+    #[test]
+    #[cfg(feature = "std_detect_file_io")]
+    fn auxv_dump_procfs() {
+        if let Ok(auxvec) = auxv_from_file("/proc/self/auxv") {
+            println!("{:?}", auxvec);
+        } else {
+            println!("reading /proc/self/auxv failed!");
+        }
+    }
+
+    #[test]
+    fn auxv_crate_procfs() {
+        let v = auxv();
+        if let Some(hwcap) = auxv_crate_getprocfs(AT_HWCAP) {
+            assert_eq!(v.unwrap().hwcap, hwcap);
+        }
+
+        // Targets with AT_HWCAP and AT_HWCAP2:
+        #[cfg(any(target_arch = "arm", target_arch = "powerpc64"))]
+        {
+            if let Some(hwcap2) = auxv_crate_getprocfs(AT_HWCAP2) {
+                assert_eq!(v.unwrap().hwcap2, hwcap2);
+            }
+        }
+    }
+}