sys/info: more CPU feature detection for RISC-V

2026-08-05 15:18:49 +00:00 · 2024-09-02 14:06:19 +00:00
parent 28c643d23f
commit 35731e66cf
6 changed files with 297 additions and 29 deletions
@@ -8,35 +8,102 @@ import "core:sys/linux"

@(init, private)
 init_cpu_features :: proc() {
-	fd, err := linux.open("/proc/self/auxv", {})
-	if err != .NONE { return }
-	defer linux.close(fd)
+	_features: CPU_Features
+	defer cpu_features = _features

-	// This is probably enough right?
-	buf: [4096]byte
-	n, rerr := linux.read(fd, buf[:])
-	if rerr != .NONE || n == 0 { return }
+	HWCAP_Bits :: enum u64 {
+		I = 'I' - 'A',
+		M = 'M' - 'A',
+		A = 'A' - 'A',
+		F = 'F' - 'A',
+		D = 'D' - 'A',
+		C = 'C' - 'A',
+		V = 'V' - 'A',
+	}
+	HWCAP :: bit_set[HWCAP_Bits; u64]

-	ulong     :: u64
-	AT_HWCAP  :: 16
+	// Read HWCAP for base extensions, we can get this info through hwprobe too but that is Linux 6.4+ only.
+	{
+		fd, err := linux.open("/proc/self/auxv", {})
+		if err != .NONE { return }
+		defer linux.close(fd)

-	// TODO: using these we could get more information than just the basics.
-	// AT_HWCAP2 :: 26
-	// AT_HWCAP3 :: 29
-	// AT_HWCAP4 :: 30
+		// This is probably enough right?
+		buf: [4096]byte
+		n, rerr := linux.read(fd, buf[:])
+		if rerr != .NONE || n == 0 { return }

-	auxv := buf[:n]
-	for len(auxv) >= size_of(ulong)*2 {
-		key := intrinsics.unaligned_load((^ulong)(&auxv[0]))
-		val := intrinsics.unaligned_load((^ulong)(&auxv[size_of(ulong)]))
-		auxv = auxv[2*size_of(ulong):]
+		ulong     :: u64
+		AT_HWCAP  :: 16

-		if key != AT_HWCAP {
-			continue
+		auxv := buf[:n]
+		for len(auxv) >= size_of(ulong)*2 {
+			key := intrinsics.unaligned_load((^ulong)(&auxv[0]))
+			val := intrinsics.unaligned_load((^ulong)(&auxv[size_of(ulong)]))
+			auxv = auxv[2*size_of(ulong):]
+
+			if key != AT_HWCAP {
+				continue
+			}
+
+			cap := transmute(HWCAP)(val)
+			if .I in cap {
+				_features += { .I }
+			}
+			if .M in cap {
+				_features += { .M }
+			}
+			if .A in cap {
+				_features += { .A }
+			}
+			if .F in cap {
+				_features += { .F }
+			}
+			if .D in cap {
+				_features += { .D }
+			}
+			if .C in cap {
+				_features += { .C }
+			}
+			if .V in cap {
+				_features += { .V }
+			}
+			break
+		}
+	}
+
+	// hwprobe for other features.
+	{
+		pairs := []linux.RISCV_HWProbe{
+			{ key = .IMA_EXT_0 },
+			{ key = .CPUPERF_0 },
+			{ key = .MISALIGNED_SCALAR_PERF },
+		}
+		err := linux.riscv_hwprobe(raw_data(pairs), len(pairs), 0, nil, {})
+		if err != nil {
+			assert(err == .ENOSYS, "unexpected error from riscv_hwprobe()")
+			return
 		}

-		cpu_features = transmute(CPU_Features)(val)
-		break
+		assert(pairs[0].key == .IMA_EXT_0)
+		exts := pairs[0].value.ima_ext_0
+		exts -= { .FD, .C, .V }
+		_features += transmute(CPU_Features)exts
+
+		if pairs[2].key == .MISALIGNED_SCALAR_PERF {
+			if pairs[2].value.misaligned_scalar_perf == .FAST {
+				_features += { .Misaligned_Supported, .Misaligned_Fast }
+			} else if pairs[2].value.misaligned_scalar_perf != .UNSUPPORTED {
+				_features += { .Misaligned_Supported }
+			}
+		} else {
+			assert(pairs[1].key == .CPUPERF_0)
+			if .FAST in pairs[1].value.cpu_perf_0 {
+				_features += { .Misaligned_Supported, .Misaligned_Fast }
+			} else if .UNSUPPORTED not_in pairs[1].value.cpu_perf_0 {
+				_features += { .Misaligned_Supported }
+			}
+		}
 	}
 }