diff --git a/cpu/cpu.go b/cpu/cpu.go index ec07aab05..02609d5b2 100644 --- a/cpu/cpu.go +++ b/cpu/cpu.go @@ -201,6 +201,25 @@ var S390X struct { _ CacheLinePad } +// RISCV64 contains the supported CPU features and performance characteristics for riscv64 +// platforms. The booleans in RISCV64, with the exception of HasFastMisaligned, indicate +// the presence of RISC-V extensions. +// +// It is safe to assume that all the RV64G extensions are supported and so they are omitted from +// this structure. As riscv64 Go programs require at least RV64G, the code that populates +// this structure cannot run successfully if some of the RV64G extensions are missing. +// The struct is padded to avoid false sharing. +var RISCV64 struct { + _ CacheLinePad + HasFastMisaligned bool // Fast misaligned accesses + HasC bool // Compressed instruction-set extension + HasV bool // Vector extension compatible with RVV 1.0 + HasZba bool // Address generation instructions extension + HasZbb bool // Basic bit-manipulation extension + HasZbs bool // Single-bit instructions extension + _ CacheLinePad +} + func init() { archInit() initOptions() diff --git a/cpu/cpu_linux_noinit.go b/cpu/cpu_linux_noinit.go index cd63e7335..7d902b684 100644 --- a/cpu/cpu_linux_noinit.go +++ b/cpu/cpu_linux_noinit.go @@ -2,7 +2,7 @@ // Use of this source code is governed by a BSD-style // license that can be found in the LICENSE file. -//go:build linux && !arm && !arm64 && !mips64 && !mips64le && !ppc64 && !ppc64le && !s390x +//go:build linux && !arm && !arm64 && !mips64 && !mips64le && !ppc64 && !ppc64le && !s390x && !riscv64 package cpu diff --git a/cpu/cpu_linux_riscv64.go b/cpu/cpu_linux_riscv64.go new file mode 100644 index 000000000..cb4a0c572 --- /dev/null +++ b/cpu/cpu_linux_riscv64.go @@ -0,0 +1,137 @@ +// Copyright 2024 The Go Authors. All rights reserved. +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +package cpu + +import ( + "syscall" + "unsafe" +) + +// RISC-V extension discovery code for Linux. The approach here is to first try the riscv_hwprobe +// syscall falling back to HWCAP to check for the C extension if riscv_hwprobe is not available. +// +// A note on detection of the Vector extension using HWCAP. +// +// Support for the Vector extension version 1.0 was added to the Linux kernel in release 6.5. +// Support for the riscv_hwprobe syscall was added in 6.4. It follows that if the riscv_hwprobe +// syscall is not available then neither is the Vector extension (which needs kernel support). +// The riscv_hwprobe syscall should then be all we need to detect the Vector extension. +// However, some RISC-V board manufacturers ship boards with an older kernel on top of which +// they have back-ported various versions of the Vector extension patches but not the riscv_hwprobe +// patches. These kernels advertise support for the Vector extension using HWCAP. Falling +// back to HWCAP to detect the Vector extension, if riscv_hwprobe is not available, or simply not +// bothering with riscv_hwprobe at all and just using HWCAP may then seem like an attractive option. +// +// Unfortunately, simply checking the 'V' bit in AT_HWCAP will not work as this bit is used by +// RISC-V board and cloud instance providers to mean different things. The Lichee Pi 4A board +// and the Scaleway RV1 cloud instances use the 'V' bit to advertise their support for the unratified +// 0.7.1 version of the Vector Specification. The Banana Pi BPI-F3 and the CanMV-K230 board use +// it to advertise support for 1.0 of the Vector extension. Versions 0.7.1 and 1.0 of the Vector +// extension are binary incompatible. HWCAP can then not be used in isolation to populate the +// HasV field as this field indicates that the underlying CPU is compatible with RVV 1.0. +// +// There is a way at runtime to distinguish between versions 0.7.1 and 1.0 of the Vector +// specification by issuing a RVV 1.0 vsetvli instruction and checking the vill bit of the vtype +// register. This check would allow us to safely detect version 1.0 of the Vector extension +// with HWCAP, if riscv_hwprobe were not available. However, the check cannot +// be added until the assembler supports the Vector instructions. +// +// Note the riscv_hwprobe syscall does not suffer from these ambiguities by design as all of the +// extensions it advertises support for are explicitly versioned. It's also worth noting that +// the riscv_hwprobe syscall is the only way to detect multi-letter RISC-V extensions, e.g., Zba. +// These cannot be detected using HWCAP and so riscv_hwprobe must be used to detect the majority +// of RISC-V extensions. +// +// Please see https://docs.kernel.org/arch/riscv/hwprobe.html for more information. + +// golang.org/x/sys/cpu is not allowed to depend on golang.org/x/sys/unix so we must +// reproduce the constants, types and functions needed to make the riscv_hwprobe syscall +// here. + +const ( + // Copied from golang.org/x/sys/unix/ztypes_linux_riscv64.go. + riscv_HWPROBE_KEY_IMA_EXT_0 = 0x4 + riscv_HWPROBE_IMA_C = 0x2 + riscv_HWPROBE_IMA_V = 0x4 + riscv_HWPROBE_EXT_ZBA = 0x8 + riscv_HWPROBE_EXT_ZBB = 0x10 + riscv_HWPROBE_EXT_ZBS = 0x20 + riscv_HWPROBE_KEY_CPUPERF_0 = 0x5 + riscv_HWPROBE_MISALIGNED_FAST = 0x3 + riscv_HWPROBE_MISALIGNED_MASK = 0x7 +) + +const ( + // sys_RISCV_HWPROBE is copied from golang.org/x/sys/unix/zsysnum_linux_riscv64.go. + sys_RISCV_HWPROBE = 258 +) + +// riscvHWProbePairs is copied from golang.org/x/sys/unix/ztypes_linux_riscv64.go. +type riscvHWProbePairs struct { + key int64 + value uint64 +} + +const ( + // CPU features + hwcap_RISCV_ISA_C = 1 << ('C' - 'A') +) + +func doinit() { + // A slice of key/value pair structures is passed to the RISCVHWProbe syscall. The key + // field should be initialised with one of the key constants defined above, e.g., + // RISCV_HWPROBE_KEY_IMA_EXT_0. The syscall will set the value field to the appropriate value. + // If the kernel does not recognise a key it will set the key field to -1 and the value field to 0. + + pairs := []riscvHWProbePairs{ + {riscv_HWPROBE_KEY_IMA_EXT_0, 0}, + {riscv_HWPROBE_KEY_CPUPERF_0, 0}, + } + + // This call only indicates that extensions are supported if they are implemented on all cores. + if riscvHWProbe(pairs, 0) { + if pairs[0].key != -1 { + v := uint(pairs[0].value) + RISCV64.HasC = isSet(v, riscv_HWPROBE_IMA_C) + RISCV64.HasV = isSet(v, riscv_HWPROBE_IMA_V) + RISCV64.HasZba = isSet(v, riscv_HWPROBE_EXT_ZBA) + RISCV64.HasZbb = isSet(v, riscv_HWPROBE_EXT_ZBB) + RISCV64.HasZbs = isSet(v, riscv_HWPROBE_EXT_ZBS) + } + if pairs[1].key != -1 { + v := pairs[1].value & riscv_HWPROBE_MISALIGNED_MASK + RISCV64.HasFastMisaligned = v == riscv_HWPROBE_MISALIGNED_FAST + } + } + + // Let's double check with HWCAP if the C extension does not appear to be supported. + // This may happen if we're running on a kernel older than 6.4. + + if !RISCV64.HasC { + RISCV64.HasC = isSet(hwCap, hwcap_RISCV_ISA_C) + } +} + +func isSet(hwc uint, value uint) bool { + return hwc&value != 0 +} + +// riscvHWProbe is a simplified version of the generated wrapper function found in +// golang.org/x/sys/unix/zsyscall_linux_riscv64.go. We simplify it by removing the +// cpuCount and cpus parameters which we do not need. We always want to pass 0 for +// these parameters here so the kernel only reports the extensions that are present +// on all cores. +func riscvHWProbe(pairs []riscvHWProbePairs, flags uint) bool { + var _zero uintptr + var p0 unsafe.Pointer + if len(pairs) > 0 { + p0 = unsafe.Pointer(&pairs[0]) + } else { + p0 = unsafe.Pointer(&_zero) + } + + _, _, e1 := syscall.Syscall6(sys_RISCV_HWPROBE, uintptr(p0), uintptr(len(pairs)), uintptr(0), uintptr(0), uintptr(flags), 0) + return e1 == 0 +} diff --git a/cpu/cpu_riscv64.go b/cpu/cpu_riscv64.go index 7f0c79c00..aca3199c9 100644 --- a/cpu/cpu_riscv64.go +++ b/cpu/cpu_riscv64.go @@ -8,4 +8,13 @@ package cpu const cacheLineSize = 64 -func initOptions() {} +func initOptions() { + options = []option{ + {Name: "fastmisaligned", Feature: &RISCV64.HasFastMisaligned}, + {Name: "c", Feature: &RISCV64.HasC}, + {Name: "v", Feature: &RISCV64.HasV}, + {Name: "zba", Feature: &RISCV64.HasZba}, + {Name: "zbb", Feature: &RISCV64.HasZbb}, + {Name: "zbs", Feature: &RISCV64.HasZbs}, + } +} diff --git a/cpu/cpu_test.go b/cpu/cpu_test.go index ba2555150..7a9bac7e5 100644 --- a/cpu/cpu_test.go +++ b/cpu/cpu_test.go @@ -61,6 +61,14 @@ func TestMIPS64Initialized(t *testing.T) { } } +func TestRISCV64Initialized(t *testing.T) { + if runtime.GOARCH == "riscv64" { + if !cpu.Initialized { + t.Fatal("Initialized expected true, got false") + } + } +} + // On ppc64x, the ISA bit for POWER8 should always be set on POWER8 and beyond. func TestPPC64minimalFeatures(t *testing.T) { // Do not run this with gccgo on ppc64, as it doesn't have POWER8 as a minimum