[BPF] add target feature allows-misaligned-mem-access

Author: clairechingching

compiler/rustc_codegen_llvm/src/llvm_util.rs

@@ -252,7 +252,10 @@ pub(crate) fn to_llvm_features<'a>(sess: &Session, s: &'a str) -> Option<LLVMFea
             "fp16" => Some(LLVMFeature::new("fullfp16")),
             s => Some(LLVMFeature::new(s)),
         },
-
+        Arch::Bpf => match s {
+            "allows-misaligned-mem-access" if major < 22 => None,
+            s => Some(LLVMFeature::new(s)),
+        },
         // Filter out features that are not supported by the current LLVM version
         Arch::LoongArch32 | Arch::LoongArch64 => match s {
             "32s" if major < 21 => None,

compiler/rustc_target/src/target_features.rs

@@ -756,8 +756,10 @@ static WASM_FEATURES: &[(&str, Stability, ImpliedFeatures)] = &[
     // tidy-alphabetical-end
 ];
 
-const BPF_FEATURES: &[(&str, Stability, ImpliedFeatures)] =
-    &[("alu32", Unstable(sym::bpf_target_feature), &[])];
+const BPF_FEATURES: &[(&str, Stability, ImpliedFeatures)] = &[
+    ("alu32", Unstable(sym::bpf_target_feature), &[]),
+    ("allows-misaligned-mem-access", Unstable(sym::bpf_target_feature), &[]),
+];
 
 static CSKY_FEATURES: &[(&str, Stability, ImpliedFeatures)] = &[
     // tidy-alphabetical-start

src/tools/rust-analyzer/crates/hir-ty/src/target_feature.rs

@@ -217,6 +217,7 @@ const TARGET_FEATURE_IMPLICATIONS_RAW: &[(&str, &[&str])] = &[
     ("relaxed-simd", &["simd128"]),
     // BPF
     ("alu32", &[]),
+    ("allows-misaligned-mem-access", &[]),
     // CSKY
     ("10e60", &["7e10"]),
     ("2e3", &["e2"]),

tests/assembly-llvm/bpf_unaligned.rs

@@ -0,0 +1,27 @@
+//@ add-minicore
+//@ assembly-output: emit-asm
+//@ compile-flags: --target bpfel-unknown-none -C target_feature=+allows-misaligned-mem-access
+//@ min-llvm-version: 22
+//@ needs-llvm-components: bpf
+#![feature(no_core)]
+#![crate_type = "rlib"]
+#![no_core]
+
+extern crate minicore;
+use minicore::*;
+
+// CHECK-LABEL: test_load_i64:
+// CHECK:       r0 = *(u64 *)(r1 + 0)
+#[no_mangle]
+pub unsafe fn test_load_i64(p: *const u64) -> u64 {
+    let mut tmp: u64 = 0;
+    copy_nonoverlapping(p as *const u8, &mut tmp as *mut u64 as *mut u8, 8);
+    tmp
+}
+
+// CHECK-LABEL: test_store_i64:
+// CHECK:       *(u64 *)(r1 + 0) = r2
+#[no_mangle]
+pub unsafe fn test_store_i64(p: *mut u64, v: u64) {
+    copy_nonoverlapping(&v as *const u64 as *const u8, p as *mut u8, 8);
+}

tests/auxiliary/minicore.rs

@@ -275,6 +275,10 @@ trait Drop {
     fn drop(&mut self);
 }
 
+#[rustc_nounwind]
+#[rustc_intrinsic]
+pub const unsafe fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: usize);
+
 pub mod mem {
     #[rustc_nounwind]
     #[rustc_intrinsic]

tests/codegen-llvm/bpf-allows-unaligned.rs

@@ -0,0 +1,11 @@
+//@ only-bpf
+#![crate_type = "lib"]
+#![feature(bpf_target_feature)]
+#![no_std]
+
+#[no_mangle]
+#[target_feature(enable = "allows-misaligned-mem-access")]
+// CHECK: define noundef zeroext i8 @foo(i8 noundef returned %arg) unnamed_addr #0 {
+pub unsafe fn foo(arg: u8) -> u8 {
+    arg
+}

tests/ui/check-cfg/target_feature.stderr

@@ -17,6 +17,7 @@ LL |     cfg!(target_feature = "_UNEXPECTED_VALUE");
 `addsubiw`
 `adx`
 `aes`
+`allows-misaligned-mem-access`
 `altivec`
 `alu32`
 `amx-avx512`