cranelift: Native feature detection for RISC-V (#5044)

* cranelift: Native feature detection for RISC-V

* cranelift: Typo fix

Thanks @cfallin

cranelift/filetests/src/test_run.rs

@@ -47,30 +47,6 @@ fn build_host_isa(
     builder.finish(flags).unwrap()
 }
 
-fn is_riscv64_compatible(
-    host: target_lexicon::Riscv64Architecture,
-    req: target_lexicon::Riscv64Architecture,
-) -> bool {
-    match host {
-        // Riscv64gc is short for RV64IMAFDCZicsr_Zifencei.
-        // So can run them all.
-        target_lexicon::Riscv64Architecture::Riscv64gc => true,
-        // Riscv64imac can run when req is not Riscv64gc.
-        target_lexicon::Riscv64Architecture::Riscv64imac
-            if req != target_lexicon::Riscv64Architecture::Riscv64gc =>
-        {
-            true
-        }
-        // Riscv64 is just basic extension.
-        target_lexicon::Riscv64Architecture::Riscv64
-            if req == target_lexicon::Riscv64Architecture::Riscv64 =>
-        {
-            true
-        }
-        _ => false,
-    }
-}
-
 /// Checks if the host's ISA is compatible with the one requested by the test.
 fn is_isa_compatible(
     file_path: &str,
@@ -85,8 +61,7 @@ fn is_isa_compatible(
 
     match (host_arch, requested_arch) {
         (host, requested) if host == requested => {}
-        (Architecture::Riscv64(host), Architecture::Riscv64(req))
+        (Architecture::Riscv64(_), Architecture::Riscv64(_)) => {}
-            if is_riscv64_compatible(host, req) => {}
         _ => {
             return Err(format!(
                 "skipped {}: host can't run {:?} programs",

cranelift/native/Cargo.toml

@@ -14,7 +14,7 @@ edition.workspace = true
 cranelift-codegen = { workspace = true, default-features = false }
 target-lexicon = { workspace = true }
 
-[target.'cfg(target_arch = "s390x")'.dependencies]
+[target.'cfg(any(target_arch = "s390x", target_arch = "riscv64"))'.dependencies]
 libc = "0.2.95"
 
 [features]

cranelift/native/src/lib.rs

@@ -165,6 +165,58 @@ pub fn builder_with_options(infer_native_flags: bool) -> Result<isa::Builder, &'
         }
     }
 
+    // `is_riscv_feature_detected` is nightly only for now, use
+    // getauxval from the libc crate directly as a temporary measure.
+    #[cfg(all(target_arch = "riscv64", target_os = "linux"))]
+    {
+        use cranelift_codegen::settings::Configurable;
+
+        if !infer_native_flags {
+            return Ok(isa_builder);
+        }
+
+        let v = unsafe { libc::getauxval(libc::AT_HWCAP) };
+
+        const HWCAP_RISCV_EXT_A: libc::c_ulong = 1 << (b'a' - b'a');
+        const HWCAP_RISCV_EXT_C: libc::c_ulong = 1 << (b'c' - b'a');
+        const HWCAP_RISCV_EXT_D: libc::c_ulong = 1 << (b'd' - b'a');
+        const HWCAP_RISCV_EXT_F: libc::c_ulong = 1 << (b'f' - b'a');
+        const HWCAP_RISCV_EXT_M: libc::c_ulong = 1 << (b'm' - b'a');
+        const HWCAP_RISCV_EXT_V: libc::c_ulong = 1 << (b'v' - b'a');
+
+        if (v & HWCAP_RISCV_EXT_A) != 0 {
+            isa_builder.enable("has_a").unwrap();
+        }
+
+        if (v & HWCAP_RISCV_EXT_C) != 0 {
+            isa_builder.enable("has_c").unwrap();
+        }
+
+        if (v & HWCAP_RISCV_EXT_D) != 0 {
+            isa_builder.enable("has_d").unwrap();
+        }
+
+        if (v & HWCAP_RISCV_EXT_F) != 0 {
+            isa_builder.enable("has_f").unwrap();
+
+            // TODO: There doesn't seem to be a bit associated with this extension
+            // rust enables it with the `f` extension:
+            // https://github.com/rust-lang/stdarch/blob/790411f93c4b5eada3c23abb4c9a063fb0b24d99/crates/std_detect/src/detect/os/linux/riscv.rs#L43
+            isa_builder.enable("has_zicsr").unwrap();
+        }
+
+        if (v & HWCAP_RISCV_EXT_M) != 0 {
+            isa_builder.enable("has_m").unwrap();
+        }
+
+        if (v & HWCAP_RISCV_EXT_V) != 0 {
+            isa_builder.enable("has_v").unwrap();
+        }
+
+        // TODO: ZiFencei does not have a bit associated with it
+        // TODO: Zbkb does not have a bit associated with it
+    }
+
     // squelch warnings about unused mut/variables on some platforms.
     drop(&mut isa_builder);
     drop(infer_native_flags);