Implement SHA256 SIMD intrinsics on x86

It'd be useful to be able to verify code implementing SHA256 using SIMD
since such code is a bit more complicated and at some points requires
use of pointers. Until now `miri` didn't support x86 SHA256 intrinsics.
This commit implements them.

src/shims/x86/mod.rs

@@ -15,6 +15,7 @@ mod aesni;
 mod avx;
 mod avx2;
 mod bmi;
+mod sha;
 mod sse;
 mod sse2;
 mod sse3;
@@ -105,6 +106,11 @@ pub(super) trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
                     this, link_name, abi, args, dest,
                 );
             }
+            name if name.starts_with("sha") => {
+                return sha::EvalContextExt::emulate_x86_sha_intrinsic(
+                    this, link_name, abi, args, dest,
+                );
+            }
             name if name.starts_with("sse.") => {
                 return sse::EvalContextExt::emulate_x86_sse_intrinsic(
                     this, link_name, abi, args, dest,

src/shims/x86/sha.rs

@@ -0,0 +1,221 @@
+//! Implements sha256 SIMD instructions of x86 targets
+//!
+//! The functions that actually compute SHA256 were copied from [RustCrypto's sha256 module].
+//!
+//! [RustCrypto's sha256 module]: https://github.com/RustCrypto/hashes/blob/6be8466247e936c415d8aafb848697f39894a386/sha2/src/sha256/soft.rs
+
+use rustc_span::Symbol;
+use rustc_target::spec::abi::Abi;
+
+use crate::*;
+
+impl<'tcx> EvalContextExt<'tcx> for crate::MiriInterpCx<'tcx> {}
+pub(super) trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
+    fn emulate_x86_sha_intrinsic(
+        &mut self,
+        link_name: Symbol,
+        abi: Abi,
+        args: &[OpTy<'tcx>],
+        dest: &MPlaceTy<'tcx>,
+    ) -> InterpResult<'tcx, EmulateItemResult> {
+        let this = self.eval_context_mut();
+        this.expect_target_feature_for_intrinsic(link_name, "sha")?;
+        // Prefix should have already been checked.
+        let unprefixed_name = link_name.as_str().strip_prefix("llvm.x86.sha").unwrap();
+
+        fn read<'c>(this: &mut MiriInterpCx<'c>, reg: &MPlaceTy<'c>) -> InterpResult<'c, [u32; 4]> {
+            let mut res = [0; 4];
+            // We reverse the order because x86 is little endian but the copied implementation uses
+            // big endian.
+            for (i, dst) in res.iter_mut().rev().enumerate() {
+                let projected = &this.project_index(reg, i.try_into().unwrap())?;
+                *dst = this.read_scalar(projected)?.to_u32()?
+            }
+            Ok(res)
+        }
+
+        fn write<'c>(
+            this: &mut MiriInterpCx<'c>,
+            dest: &MPlaceTy<'c>,
+            val: [u32; 4],
+        ) -> InterpResult<'c, ()> {
+            // We reverse the order because x86 is little endian but the copied implementation uses
+            // big endian.
+            for (i, part) in val.into_iter().rev().enumerate() {
+                let projected = &this.project_index(dest, i.try_into().unwrap())?;
+                this.write_scalar(Scalar::from_u32(part), projected)?;
+            }
+            Ok(())
+        }
+
+        match unprefixed_name {
+            // Used to implement the _mm_sha256rnds2_epu32 function.
+            "256rnds2" => {
+                let [a, b, k] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
+
+                let (a_reg, a_len) = this.operand_to_simd(a)?;
+                let (b_reg, b_len) = this.operand_to_simd(b)?;
+                let (k_reg, k_len) = this.operand_to_simd(k)?;
+                let (dest, dest_len) = this.mplace_to_simd(dest)?;
+
+                assert_eq!(a_len, 4);
+                assert_eq!(b_len, 4);
+                assert_eq!(k_len, 4);
+                assert_eq!(dest_len, 4);
+
+                let a = read(this, &a_reg)?;
+                let b = read(this, &b_reg)?;
+                let k = read(this, &k_reg)?;
+
+                let result = sha256rnds2_epu32(a, b, k);
+                write(this, &dest, result)?;
+            }
+            // Used to implement the _mm_sha256msg1_epu32 function.
+            "256msg1" => {
+                let [a, b] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
+
+                let (a_reg, a_len) = this.operand_to_simd(a)?;
+                let (b_reg, b_len) = this.operand_to_simd(b)?;
+                let (dest, dest_len) = this.mplace_to_simd(dest)?;
+
+                assert_eq!(a_len, 4);
+                assert_eq!(b_len, 4);
+                assert_eq!(dest_len, 4);
+
+                let a = read(this, &a_reg)?;
+                let b = read(this, &b_reg)?;
+
+                let result = sha256msg1_epu32(a, b);
+                write(this, &dest, result)?;
+            }
+            // Used to implement the _mm_sha256msg2_epu32 function.
+            "256msg2" => {
+                let [a, b] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
+
+                let (a_reg, a_len) = this.operand_to_simd(a)?;
+                let (b_reg, b_len) = this.operand_to_simd(b)?;
+                let (dest, dest_len) = this.mplace_to_simd(dest)?;
+
+                assert_eq!(a_len, 4);
+                assert_eq!(b_len, 4);
+                assert_eq!(dest_len, 4);
+
+                let a = read(this, &a_reg)?;
+                let b = read(this, &b_reg)?;
+
+                let result = sha256msg2_epu32(a, b);
+                write(this, &dest, result)?;
+            }
+            _ => return Ok(EmulateItemResult::NotSupported),
+        }
+        Ok(EmulateItemResult::NeedsReturn)
+    }
+}
+
+#[inline(always)]
+fn shr(v: [u32; 4], o: u32) -> [u32; 4] {
+    [v[0] >> o, v[1] >> o, v[2] >> o, v[3] >> o]
+}
+
+#[inline(always)]
+fn shl(v: [u32; 4], o: u32) -> [u32; 4] {
+    [v[0] << o, v[1] << o, v[2] << o, v[3] << o]
+}
+
+#[inline(always)]
+fn or(a: [u32; 4], b: [u32; 4]) -> [u32; 4] {
+    [a[0] | b[0], a[1] | b[1], a[2] | b[2], a[3] | b[3]]
+}
+
+#[inline(always)]
+fn xor(a: [u32; 4], b: [u32; 4]) -> [u32; 4] {
+    [a[0] ^ b[0], a[1] ^ b[1], a[2] ^ b[2], a[3] ^ b[3]]
+}
+
+#[inline(always)]
+fn add(a: [u32; 4], b: [u32; 4]) -> [u32; 4] {
+    [
+        a[0].wrapping_add(b[0]),
+        a[1].wrapping_add(b[1]),
+        a[2].wrapping_add(b[2]),
+        a[3].wrapping_add(b[3]),
+    ]
+}
+
+fn sha256load(v2: [u32; 4], v3: [u32; 4]) -> [u32; 4] {
+    [v3[3], v2[0], v2[1], v2[2]]
+}
+
+fn sha256rnds2_epu32(cdgh: [u32; 4], abef: [u32; 4], wk: [u32; 4]) -> [u32; 4] {
+    macro_rules! big_sigma0 {
+        ($a:expr) => {
+            ($a.rotate_right(2) ^ $a.rotate_right(13) ^ $a.rotate_right(22))
+        };
+    }
+    macro_rules! big_sigma1 {
+        ($a:expr) => {
+            ($a.rotate_right(6) ^ $a.rotate_right(11) ^ $a.rotate_right(25))
+        };
+    }
+    macro_rules! bool3ary_202 {
+        ($a:expr, $b:expr, $c:expr) => {
+            $c ^ ($a & ($b ^ $c))
+        };
+    } // Choose, MD5F, SHA1C
+    macro_rules! bool3ary_232 {
+        ($a:expr, $b:expr, $c:expr) => {
+            ($a & $b) ^ ($a & $c) ^ ($b & $c)
+        };
+    } // Majority, SHA1M
+
+    let [_, _, wk1, wk0] = wk;
+    let [a0, b0, e0, f0] = abef;
+    let [c0, d0, g0, h0] = cdgh;
+
+    // a round
+    let x0 =
+        big_sigma1!(e0).wrapping_add(bool3ary_202!(e0, f0, g0)).wrapping_add(wk0).wrapping_add(h0);
+    let y0 = big_sigma0!(a0).wrapping_add(bool3ary_232!(a0, b0, c0));
+    let (a1, b1, c1, d1, e1, f1, g1, h1) =
+        (x0.wrapping_add(y0), a0, b0, c0, x0.wrapping_add(d0), e0, f0, g0);
+
+    // a round
+    let x1 =
+        big_sigma1!(e1).wrapping_add(bool3ary_202!(e1, f1, g1)).wrapping_add(wk1).wrapping_add(h1);
+    let y1 = big_sigma0!(a1).wrapping_add(bool3ary_232!(a1, b1, c1));
+    let (a2, b2, _, _, e2, f2, _, _) =
+        (x1.wrapping_add(y1), a1, b1, c1, x1.wrapping_add(d1), e1, f1, g1);
+
+    [a2, b2, e2, f2]
+}
+
+fn sha256msg1_epu32(v0: [u32; 4], v1: [u32; 4]) -> [u32; 4] {
+    // sigma 0 on vectors
+    #[inline]
+    fn sigma0x4(x: [u32; 4]) -> [u32; 4] {
+        let t1 = or(shr(x, 7), shl(x, 25));
+        let t2 = or(shr(x, 18), shl(x, 14));
+        let t3 = shr(x, 3);
+        xor(xor(t1, t2), t3)
+    }
+
+    add(v0, sigma0x4(sha256load(v0, v1)))
+}
+
+fn sha256msg2_epu32(v4: [u32; 4], v3: [u32; 4]) -> [u32; 4] {
+    macro_rules! sigma1 {
+        ($a:expr) => {
+            $a.rotate_right(17) ^ $a.rotate_right(19) ^ ($a >> 10)
+        };
+    }
+
+    let [x3, x2, x1, x0] = v4;
+    let [w15, w14, _, _] = v3;
+
+    let w16 = x0.wrapping_add(sigma1!(w14));
+    let w17 = x1.wrapping_add(sigma1!(w15));
+    let w18 = x2.wrapping_add(sigma1!(w16));
+    let w19 = x3.wrapping_add(sigma1!(w17));
+
+    [w19, w18, w17, w16]
+}