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| 1 | +use rustc_middle::ty::layout::LayoutOf; |
| 2 | +use rustc_target::abi::Endian; |
| 3 | + |
| 4 | +use crate::*; |
| 5 | + |
| 6 | +/// The maximum number of CPUs supported by miri. |
| 7 | +/// |
| 8 | +/// This value is compatible with the libc `CPU_SETSIZE` constant and corresponds to the number |
| 9 | +/// of CPUs that a `cpu_set_t` can contain. |
| 10 | +/// |
| 11 | +/// Real machines can have more CPUs than this number, and there exist APIs to set their affinity, |
| 12 | +/// but this is not currently supported by miri. |
| 13 | +pub const MAX_CPUS: usize = 1024; |
| 14 | + |
| 15 | +/// A thread's CPU affinity mask determines the set of CPUs on which it is eligible to run. |
| 16 | +// the actual representation depends on the target's endianness and pointer width. |
| 17 | +// See CpuAffinityMask::set for details |
| 18 | +#[derive(Clone)] |
| 19 | +pub(crate) struct CpuAffinityMask([u8; Self::CPU_MASK_BYTES]); |
| 20 | + |
| 21 | +impl CpuAffinityMask { |
| 22 | + pub(crate) const CPU_MASK_BYTES: usize = MAX_CPUS / 8; |
| 23 | + |
| 24 | + pub fn new<'tcx>(cx: &impl LayoutOf<'tcx>, cpu_count: u32) -> Self { |
| 25 | + let mut this = Self([0; Self::CPU_MASK_BYTES]); |
| 26 | + |
| 27 | + // the default affinity mask includes only the available CPUs |
| 28 | + for i in 0..cpu_count as usize { |
| 29 | + this.set(cx, i); |
| 30 | + } |
| 31 | + |
| 32 | + this |
| 33 | + } |
| 34 | + |
| 35 | + pub fn chunk_size<'tcx>(cx: &impl LayoutOf<'tcx>) -> u64 { |
| 36 | + // The actual representation of the CpuAffinityMask is [c_ulong; _]. |
| 37 | + let ulong = helpers::path_ty_layout(cx, &["core", "ffi", "c_ulong"]); |
| 38 | + ulong.size.bytes() |
| 39 | + } |
| 40 | + |
| 41 | + fn set<'tcx>(&mut self, cx: &impl LayoutOf<'tcx>, cpu: usize) { |
| 42 | + // we silently ignore CPUs that are out of bounds. This matches the behavior of |
| 43 | + // `sched_setaffinity` with a mask that specifies more than `CPU_SETSIZE` CPUs. |
| 44 | + if cpu >= MAX_CPUS { |
| 45 | + return; |
| 46 | + } |
| 47 | + |
| 48 | + // The actual representation of the CpuAffinityMask is [c_ulong; _]. |
| 49 | + // Within the array elements, we need to use the endianness of the target. |
| 50 | + let target = &cx.tcx().sess.target; |
| 51 | + match Self::chunk_size(cx) { |
| 52 | + 4 => { |
| 53 | + let start = cpu / 32 * 4; // first byte of the correct u32 |
| 54 | + let chunk = self.0[start..].first_chunk_mut::<4>().unwrap(); |
| 55 | + let offset = cpu % 32; |
| 56 | + *chunk = match target.options.endian { |
| 57 | + Endian::Little => (u32::from_le_bytes(*chunk) | 1 << offset).to_le_bytes(), |
| 58 | + Endian::Big => (u32::from_be_bytes(*chunk) | 1 << offset).to_be_bytes(), |
| 59 | + }; |
| 60 | + } |
| 61 | + 8 => { |
| 62 | + let start = cpu / 64 * 8; // first byte of the correct u64 |
| 63 | + let chunk = self.0[start..].first_chunk_mut::<8>().unwrap(); |
| 64 | + let offset = cpu % 64; |
| 65 | + *chunk = match target.options.endian { |
| 66 | + Endian::Little => (u64::from_le_bytes(*chunk) | 1 << offset).to_le_bytes(), |
| 67 | + Endian::Big => (u64::from_be_bytes(*chunk) | 1 << offset).to_be_bytes(), |
| 68 | + }; |
| 69 | + } |
| 70 | + other => bug!("chunk size not supported: {other}"), |
| 71 | + }; |
| 72 | + } |
| 73 | + |
| 74 | + pub fn as_slice(&self) -> &[u8] { |
| 75 | + self.0.as_slice() |
| 76 | + } |
| 77 | + |
| 78 | + pub fn from_array<'tcx>( |
| 79 | + cx: &impl LayoutOf<'tcx>, |
| 80 | + cpu_count: u32, |
| 81 | + bytes: [u8; Self::CPU_MASK_BYTES], |
| 82 | + ) -> Option<Self> { |
| 83 | + // mask by what CPUs are actually available |
| 84 | + let default = Self::new(cx, cpu_count); |
| 85 | + let masked = std::array::from_fn(|i| bytes[i] & default.0[i]); |
| 86 | + |
| 87 | + // at least one thread must be set for the input to be valid |
| 88 | + masked.iter().any(|b| *b != 0).then_some(Self(masked)) |
| 89 | + } |
| 90 | +} |
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