cpuid.rs.html -- source
Description: Source to the Rust file `src/libcore/../stdarch/crates/core_arch/src/x86/cpuid.rs`.
Keywords: rust, rustlang, rust-lang

      1
      2
      3
      4
      5
      6
      7
      8
      9
     10
     11
     12
     13
     14
     15
     16
     17
     18
     19
     20
     21
     22
     23
     24
     25
     26
     27
     28
     29
     30
     31
     32
     33
     34
     35
     36
     37
     38
     39
     40
     41
     42
     43
     44
     45
     46
     47
     48
     49
     50
     51
     52
     53
     54
     55
     56
     57
     58
     59
     60
     61
     62
     63
     64
     65
     66
     67
     68
     69
     70
     71
     72
     73
     74
     75
     76
     77
     78
     79
     80
     81
     82
     83
     84
     85
     86
     87
     88
     89
     90
     91
     92
     93
     94
     95
     96
     97
     98
     99
    100
    101
    102
    103
    104
    105
    106
    107
    108
    109
    110
    111
    112
    113
    114
    115
    116
    117
    118
    119
    120
    121
    122
    123
    124
    125
    126
    127
    128
    129
    130
    131
    132
    133
    134
    135
    136
    137
    138
    139
    140
    141
    142
    143
    144
    145
    146
    147
    148
    149
    150
    151
    152
    153
    154
    155
    156
    157
    158
    159
    160
    161
    162
    163
    164
    165
    166
    167
    168
    169
    170
    171
    172
    173
    174
    175
    176
    177
    178
    179
    180
    181
    182
    183
    184
    185
    186
    187

    //! `cpuid` intrinsics
    #![allow(clippy::module_name_repetitions)]

    #[cfg(test)]
    use stdarch_test::assert_instr;

    /// Result of the `cpuid` instruction.
    #[allow(clippy::missing_inline_in_public_items)]
    // ^^ the derived impl of Debug for CpuidResult is not #[inline] and that's OK.
    #[derive(Copy, Clone, Debug, Eq, Ord, PartialEq, PartialOrd)]
    #[stable(feature = "simd_x86", since = "1.27.0")]
    pub struct CpuidResult {
        /// EAX register.
        #[stable(feature = "simd_x86", since = "1.27.0")]
        pub eax: u32,
        /// EBX register.
        #[stable(feature = "simd_x86", since = "1.27.0")]
        pub ebx: u32,
        /// ECX register.
        #[stable(feature = "simd_x86", since = "1.27.0")]
        pub ecx: u32,
        /// EDX register.
        #[stable(feature = "simd_x86", since = "1.27.0")]
        pub edx: u32,
    }

    /// Returns the result of the `cpuid` instruction for a given `leaf` (`EAX`)
    /// and
    /// `sub_leaf` (`ECX`).
    ///
    /// The highest-supported leaf value is returned by the first tuple argument of
    /// [`__get_cpuid_max(0)`](fn.__get_cpuid_max.html). For leaves containung
    /// sub-leaves, the second tuple argument returns the highest-supported
    /// sub-leaf
    /// value.
    ///
    /// The [CPUID Wikipedia page][wiki_cpuid] contains how to query which
    /// information using the `EAX` and `ECX` registers, and the interpretation of
    /// the results returned in `EAX`, `EBX`, `ECX`, and `EDX`.
    ///
    /// The references are:
    /// - [Intel 64 and IA-32 Architectures Software Developer's Manual Volume 2:
    ///   Instruction Set Reference, A-Z][intel64_ref].
    /// - [AMD64 Architecture Programmer's Manual, Volume 3: General-Purpose and
    ///   System Instructions][amd64_ref].
    ///
    /// [wiki_cpuid]: https://en.wikipedia.org/wiki/CPUID
    /// [intel64_ref]: http://www.intel.de/content/dam/www/public/us/en/documents/manuals/64-ia-32-architectures-software-developer-instruction-set-reference-manual-325383.pdf
    /// [amd64_ref]: http://support.amd.com/TechDocs/24594.pdf
    #[inline]
    #[cfg_attr(test, assert_instr(cpuid))]
    #[stable(feature = "simd_x86", since = "1.27.0")]
    pub unsafe fn __cpuid_count(leaf: u32, sub_leaf: u32) -> CpuidResult {
        let eax;
        let ebx;
        let ecx;
        let edx;
        #[cfg(target_arch = "x86")]
        {
            asm!("cpuid"
                 : "={eax}"(eax), "={ebx}"(ebx), "={ecx}"(ecx), "={edx}"(edx)
                 : "{eax}"(leaf), "{ecx}"(sub_leaf)
                 : :);
        }
        #[cfg(target_arch = "x86_64")]
        {
            // x86-64 uses %rbx as the base register, so preserve it.
            asm!("cpuid"
                 : "={eax}"(eax), "={ebx}"(ebx), "={ecx}"(ecx), "={edx}"(edx)
                 : "{eax}"(leaf), "{ecx}"(sub_leaf)
                 : "rbx" :);
        }
        CpuidResult { eax, ebx, ecx, edx }
    }

    /// See [`__cpuid_count`](fn.__cpuid_count.html).
    #[inline]
    #[cfg_attr(test, assert_instr(cpuid))]
    #[stable(feature = "simd_x86", since = "1.27.0")]
    pub unsafe fn __cpuid(leaf: u32) -> CpuidResult {
        __cpuid_count(leaf, 0)
    }

    /// Does the host support the `cpuid` instruction?
    #[inline]
    pub fn has_cpuid() -> bool {
        #[cfg(target_env = "sgx")]
        {
            false
        }
        #[cfg(all(not(target_env = "sgx"), target_arch = "x86_64"))]
        {
            true
        }
        #[cfg(all(not(target_env = "sgx"), target_arch = "x86"))]
        {
            // Optimization for i586 and i686 Rust targets which SSE enabled
            // and support cpuid:
            #[cfg(target_feature = "sse")]
            {
                true
            }

            // If SSE is not enabled, detect whether cpuid is available:
            #[cfg(not(target_feature = "sse"))]
            unsafe {
                // On `x86` the `cpuid` instruction is not always available.
                // This follows the approach indicated in:
                // http://wiki.osdev.org/CPUID#Checking_CPUID_availability
                // https://software.intel.com/en-us/articles/using-cpuid-to-detect-the-presence-of-sse-41-and-sse-42-instruction-sets/
                // which detects whether `cpuid` is available by checking whether
                // the 21st bit of the EFLAGS register is modifiable or not.
                // If it is, then `cpuid` is available.
                let result: u32;
                let _temp: u32;
                asm!(r#"
                     # Read eflags into $0 and copy it into $1:
                     pushfd
                     pop     $0
                     mov     $1, $0
                     # Flip 21st bit of $0.
                     xor     $0, 0x200000
                     # Set eflags to the value of $0
                     #
                     # Bit 21st can only be modified if cpuid is available
                     push    $0
                     popfd          # A
                     # Read eflags into $0:
                     pushfd         # B
                     pop     $0
                     # xor with the original eflags sets the bits that
                     # have been modified:
                     xor     $0, $1
                     "#
                     : "=r"(result), "=r"(_temp)
                     :
                     : "cc", "memory"
                     : "intel");
                // There is a race between popfd (A) and pushfd (B)
                // where other bits beyond 21st may have been modified due to
                // interrupts, a debugger stepping through the asm, etc.
                //
                // Therefore, explicitly check whether the 21st bit
                // was modified or not.
                //
                // If the result is zero, the cpuid bit was not modified.
                // If the result is `0x200000` (non-zero), then the cpuid
                // was correctly modified and the CPU supports the cpuid
                // instruction:
                (result & 0x200000) != 0
            }
        }
    }

    /// Returns the highest-supported `leaf` (`EAX`) and sub-leaf (`ECX`) `cpuid`
    /// values.
    ///
    /// If `cpuid` is supported, and `leaf` is zero, then the first tuple argument
    /// contains the highest `leaf` value that `cpuid` supports. For `leaf`s
    /// containing sub-leafs, the second tuple argument contains the
    /// highest-supported sub-leaf value.
    ///
    /// See also [`__cpuid`](fn.__cpuid.html) and
    /// [`__cpuid_count`](fn.__cpuid_count.html).
    #[inline]
    #[stable(feature = "simd_x86", since = "1.27.0")]
    pub unsafe fn __get_cpuid_max(leaf: u32) -> (u32, u32) {
        let CpuidResult { eax, ebx, .. } = __cpuid(leaf);
        (eax, ebx)
    }

    #[cfg(test)]
    mod tests {
        use crate::core_arch::x86::*;

        #[test]
        fn test_always_has_cpuid() {
            // all currently-tested targets have the instruction
            // FIXME: add targets without `cpuid` to CI
            assert!(cpuid::has_cpuid());
        }

        #[test]
        fn test_has_cpuid_idempotent() {
            assert_eq!(cpuid::has_cpuid(), cpuid::has_cpuid());
        }
    }