Turn std_detect into a no_std crate (#1005)

Author: Amanieu

crates/std_detect/src/detect/cache.rs

@@ -3,9 +3,9 @@
 
 #![allow(dead_code)] // not used on all platforms
 
-use crate::sync::atomic::Ordering;
+use core::sync::atomic::Ordering;
 
-use crate::sync::atomic::AtomicUsize;
+use core::sync::atomic::AtomicUsize;
 
 /// Sets the `bit` of `x`.
 #[inline]
@@ -125,9 +125,16 @@ cfg_if::cfg_if! {
     if #[cfg(feature = "std_detect_env_override")] {
         #[inline]
         fn initialize(mut value: Initializer) -> Initializer {
-            if let Ok(disable) = crate::env::var("RUST_STD_DETECT_UNSTABLE") {
-                for v in disable.split(" ") {
-                    let _ = super::Feature::from_str(v).map(|v| value.unset(v as u32));
+            let env = unsafe {
+                libc::getenv(b"RUST_STD_DETECT_UNSTABLE\0".as_ptr() as *const libc::c_char)
+            };
+            if !env.is_null() {
+                let len = unsafe { libc::strlen(env) };
+                let env = unsafe { core::slice::from_raw_parts(env as *const u8, len) };
+                if let Ok(disable) = core::str::from_utf8(env) {
+                    for v in disable.split(" ") {
+                        let _ = super::Feature::from_str(v).map(|v| value.unset(v as u32));
+                    }
                 }
             }
             do_initialize(value);

crates/std_detect/src/detect/mod.rs

@@ -98,10 +98,10 @@ cfg_if! {
         // On x86/x86_64 no OS specific functionality is required.
         #[path = "os/x86.rs"]
         mod os;
-    } else if #[cfg(all(target_os = "linux", feature = "use_std"))] {
+    } else if #[cfg(all(target_os = "linux", feature = "libc"))] {
         #[path = "os/linux/mod.rs"]
         mod os;
-    } else if #[cfg(all(target_os = "freebsd", feature = "use_std"))] {
+    } else if #[cfg(all(target_os = "freebsd", feature = "libc"))] {
         #[cfg(target_arch = "aarch64")]
         #[path = "os/aarch64.rs"]
         mod aarch64;
@@ -140,7 +140,7 @@ pub fn features() -> impl Iterator<Item = (&'static str, bool)> {
             target_arch = "mips64",
         ))] {
             (0_u8..Feature::_last as u8).map(|discriminant: u8| {
-                let f: Feature = unsafe { crate::mem::transmute(discriminant) };
+                let f: Feature = unsafe { core::mem::transmute(discriminant) };
                 let name: &'static str = f.to_str();
                 let enabled: bool = check_for(f);
                 (name, enabled)

crates/std_detect/src/detect/os/freebsd/auxvec.rs

@@ -42,7 +42,7 @@ pub(crate) fn auxv() -> Result<AuxVec, ()> {
 
 /// Tries to read the `key` from the auxiliary vector.
 fn archauxv(key: usize) -> Result<usize, ()> {
-    use crate::mem;
+    use core::mem;
 
     #[derive(Copy, Clone)]
     #[repr(C)]

crates/std_detect/src/detect/os/freebsd/mod.rs

@@ -5,18 +5,18 @@ mod auxvec;
 cfg_if::cfg_if! {
     if #[cfg(target_arch = "aarch64")] {
         mod aarch64;
-        pub use self::aarch64::check_for;
+        pub(crate) use self::aarch64::detect_features;
     } else if #[cfg(target_arch = "arm")] {
         mod arm;
-        pub use self::arm::check_for;
+        pub(crate) use self::arm::detect_features;
     } else if #[cfg(target_arch = "powerpc64")] {
         mod powerpc;
-        pub use self::powerpc::check_for;
+        pub(crate) use self::powerpc::detect_features;
     } else {
-        use crate::arch::detect::Feature;
+        use crate::detect::cache;
         /// Performs run-time feature detection.
-        pub fn check_for(_x: Feature) -> bool {
-            false
+        pub(crate) fn detect_features() -> cache::Initializer {
+            cache::Initializer::default()
         }
     }
 }

crates/std_detect/src/detect/os/linux/aarch64.rs

@@ -1,6 +1,6 @@
 //! Run-time feature detection for Aarch64 on Linux.
 
-use super::{auxvec, cpuinfo};
+use super::auxvec;
 use crate::detect::{bit, cache, Feature};
 
 /// Try to read the features from the auxiliary vector, and if that fails, try
@@ -10,7 +10,8 @@ pub(crate) fn detect_features() -> cache::Initializer {
         let hwcap: AtHwcap = auxv.into();
         return hwcap.cache();
     }
-    if let Ok(c) = cpuinfo::CpuInfo::new() {
+    #[cfg(feature = "std_detect_file_io")]
+    if let Ok(c) = super::cpuinfo::CpuInfo::new() {
         let hwcap: AtHwcap = c.into();
         return hwcap.cache();
     }
@@ -77,9 +78,10 @@ impl From<auxvec::AuxVec> for AtHwcap {
     }
 }
 
-impl From<cpuinfo::CpuInfo> for AtHwcap {
+#[cfg(feature = "std_detect_file_io")]
+impl From<super::cpuinfo::CpuInfo> for AtHwcap {
     /// Reads AtHwcap from /proc/cpuinfo .
-    fn from(c: cpuinfo::CpuInfo) -> Self {
+    fn from(c: super::cpuinfo::CpuInfo) -> Self {
         let f = &c.field("Features");
         AtHwcap {
             // 64-bit names. FIXME: In 32-bit compatibility mode /proc/cpuinfo will

crates/std_detect/src/detect/os/linux/arm.rs

@@ -1,6 +1,6 @@
 //! Run-time feature detection for ARM on Linux.
 
-use super::{auxvec, cpuinfo};
+use super::auxvec;
 use crate::detect::{bit, cache, Feature};
 
 /// Try to read the features from the auxiliary vector, and if that fails, try
@@ -31,7 +31,8 @@ pub(crate) fn detect_features() -> cache::Initializer {
         return value;
     }
 
-    if let Ok(c) = cpuinfo::CpuInfo::new() {
+    #[cfg(feature = "std_detect_file_io")]
+    if let Ok(c) = super::cpuinfo::CpuInfo::new() {
         enable_feature(
             &mut value,
             Feature::neon,
@@ -55,7 +56,8 @@ pub(crate) fn detect_features() -> cache::Initializer {
 /// Is the CPU known to have a broken NEON unit?
 ///
 /// See https://crbug.com/341598.
-fn has_broken_neon(cpuinfo: &cpuinfo::CpuInfo) -> bool {
+#[cfg(feature = "std_detect_file_io")]
+fn has_broken_neon(cpuinfo: &super::cpuinfo::CpuInfo) -> bool {
     cpuinfo.field("CPU implementer") == "0x51"
         && cpuinfo.field("CPU architecture") == "7"
         && cpuinfo.field("CPU variant") == "0x1"

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

@@ -1,13 +1,16 @@
 //! 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};
+pub(crate) const AT_NULL: usize = 0;
 
 /// 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"))]
+#[cfg(any(
+    target_arch = "arm",
+    target_arch = "powerpc",
+    target_arch = "powerpc64"
+))]
 pub(crate) const AT_HWCAP2: usize = 26;
 
 /// Cache HWCAP bitfields of the ELF Auxiliary Vector.
@@ -17,7 +20,11 @@ pub(crate) const AT_HWCAP2: usize = 26;
 #[derive(Debug, Copy, Clone)]
 pub(crate) struct AuxVec {
     pub hwcap: usize,
-    #[cfg(any(target_arch = "arm", target_arch = "powerpc64"))]
+    #[cfg(any(
+        target_arch = "arm",
+        target_arch = "powerpc",
+        target_arch = "powerpc64"
+    ))]
     pub hwcap2: usize,
 }
 
@@ -64,7 +71,11 @@ pub(crate) fn auxv() -> Result<AuxVec, ()> {
             }
 
             // Targets with AT_HWCAP and AT_HWCAP2:
-            #[cfg(any(target_arch = "arm", target_arch = "powerpc64"))]
+            #[cfg(any(
+                target_arch = "arm",
+                target_arch = "powerpc",
+                target_arch = "powerpc64"
+            ))]
             {
                 if let Ok(hwcap2) = getauxval(AT_HWCAP2) {
                     if hwcap != 0 && hwcap2 != 0 {
@@ -74,21 +85,11 @@ pub(crate) fn auxv() -> Result<AuxVec, ()> {
             }
             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) };
+        let hwcap = unsafe { libc::getauxval(AT_HWCAP) };
 
         // Targets with only AT_HWCAP:
         #[cfg(any(target_arch = "aarch64", target_arch = "mips", target_arch = "mips64"))]
@@ -99,14 +100,29 @@ pub(crate) fn auxv() -> Result<AuxVec, ()> {
         }
 
         // Targets with AT_HWCAP and AT_HWCAP2:
-        #[cfg(any(target_arch = "arm", target_arch = "powerpc64"))]
+        #[cfg(any(
+            target_arch = "arm",
+            target_arch = "powerpc",
+            target_arch = "powerpc64"
+        ))]
         {
-            let hwcap2 = unsafe { ffi_getauxval(AT_HWCAP2) };
+            let hwcap2 = unsafe { libc::getauxval(AT_HWCAP2) };
             if hwcap != 0 && hwcap2 != 0 {
                 return Ok(AuxVec { hwcap, hwcap2 });
             }
         }
     }
+
+    #[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(())
+    }
 }
 
 /// Tries to read the `key` from the auxiliary vector by calling the
@@ -122,7 +138,7 @@ fn getauxval(key: usize) -> Result<usize, ()> {
             return Err(());
         }
 
-        let ffi_getauxval: F = mem::transmute(ptr);
+        let ffi_getauxval: F = core::mem::transmute(ptr);
         Ok(ffi_getauxval(key))
     }
 }
@@ -131,18 +147,19 @@ fn getauxval(key: usize) -> Result<usize, ()> {
 /// 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(|_| ())?;
+    let file = super::read_file(file)?;
 
     // 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(|_| ())?;
+    let len = core::mem::size_of_val(&buf).max(file.len());
+    unsafe {
+        core::ptr::copy_nonoverlapping(file.as_ptr(), buf.as_mut_ptr() as *mut u8, len);
     }
+
     auxv_from_buf(&buf)
 }
 
@@ -155,18 +172,24 @@ fn auxv_from_buf(buf: &[usize; 64]) -> Result<AuxVec, ()> {
     {
         for el in buf.chunks(2) {
             match el[0] {
+                AT_NULL => break,
                 AT_HWCAP => return Ok(AuxVec { hwcap: el[1] }),
                 _ => (),
             }
         }
     }
     // Targets with AT_HWCAP and AT_HWCAP2:
-    #[cfg(any(target_arch = "arm", target_arch = "powerpc64"))]
+    #[cfg(any(
+        target_arch = "arm",
+        target_arch = "powerpc",
+        target_arch = "powerpc64"
+    ))]
     {
         let mut hwcap = None;
         let mut hwcap2 = None;
         for el in buf.chunks(2) {
             match el[0] {
+                AT_NULL => break,
                 AT_HWCAP => hwcap = Some(el[1]),
                 AT_HWCAP2 => hwcap2 = Some(el[1]),
                 _ => (),
@@ -214,7 +237,12 @@ mod tests {
 
     // 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")))]
+    #[cfg(any(
+        target_arch = "aarch64",
+        target_arch = "arm",
+        target_arch = "powerpc",
+        target_arch = "powerpc64"
+    ))]
     #[test]
     fn auxv_crate() {
         let v = auxv();
@@ -224,7 +252,11 @@ mod tests {
         }
 
         // Targets with AT_HWCAP and AT_HWCAP2:
-        #[cfg(any(target_arch = "arm", target_arch = "powerpc64"))]
+        #[cfg(any(
+            target_arch = "arm",
+            target_arch = "powerpc",
+            target_arch = "powerpc64"
+        ))]
         {
             if let Some(hwcap2) = auxv_crate_getauxval(AT_HWCAP2) {
                 let rt_hwcap2 = v.expect("failed to find hwcap2 key").hwcap2;
@@ -243,7 +275,7 @@ mod tests {
     }
 
     #[cfg(feature = "std_detect_file_io")]
-    cfg_if! {
+    cfg_if::cfg_if! {
         if #[cfg(target_arch = "arm")] {
             #[test]
             fn linux_rpi3() {
@@ -264,6 +296,7 @@ mod tests {
                 // want to fall back to /proc/cpuinfo in this case, so
                 // reading should fail. assert_eq!(v.hwcap, 126614527);
                 // assert_eq!(v.hwcap2, 0);
+                let _ = v;
             }
         } else if #[cfg(target_arch = "aarch64")] {
             #[test]
@@ -286,15 +319,26 @@ mod tests {
         }
     }
 
+    #[cfg(any(
+        target_arch = "aarch64",
+        target_arch = "arm",
+        target_arch = "powerpc",
+        target_arch = "powerpc64"
+    ))]
     #[test]
+    #[cfg(feature = "std_detect_file_io")]
     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"))]
+        #[cfg(any(
+            target_arch = "arm",
+            target_arch = "powerpc",
+            target_arch = "powerpc64"
+        ))]
         {
             if let Some(hwcap2) = auxv_crate_getprocfs(AT_HWCAP2) {
                 assert_eq!(v.unwrap().hwcap2, hwcap2);