Initial RISC-V support.

Co-authored-by: Alex Fan <alex.fan.q@gmail.com>

Make.inc

@@ -938,8 +938,12 @@ endif
 
 #If nothing is set default to native unless we are cross-compiling
 ifeq ($(MARCH)$(MCPU)$(MTUNE)$(JULIA_CPU_TARGET)$(XC_HOST),)
-ifeq ($(ARCH),aarch64) #ARM recommends only setting MCPU for AArch64
+ifeq ($(ARCH),aarch64)
+# ARM recommends only setting MCPU for AArch64
 MCPU=native
+else ifneq (,$(findstring riscv64,$(ARCH)))
+# RISC-V doesn't have a native option
+$(error Building for RISC-V requires a specific MARCH to be set))
 else
 MARCH=native
 MTUNE=native
@@ -995,6 +999,9 @@ endif
 ifneq (,$(findstring arm,$(ARCH)))
 DIST_ARCH:=arm
 endif
+ifneq (,$(findstring riscv64,$(ARCH)))
+DIST_ARCH:=riscv64
+endif
 
 JULIA_BINARYDIST_FILENAME := julia-$(JULIA_COMMIT)-$(DIST_OS)$(DIST_ARCH)
 endif
@@ -1018,8 +1025,12 @@ ifneq ($(MARCH),)
 CC += -march=$(MARCH)
 CXX += -march=$(MARCH)
 FC += -march=$(MARCH)
+# On RISC-V, don't forward the MARCH ISA string to JULIA_CPU_TARGET,
+# as it's always incompatible with LLVM's CPU target name parser.
+ifeq (,$(findstring riscv64,$(ARCH)))
 JULIA_CPU_TARGET ?= $(MARCH)
 endif
+endif
 
 # Set MCPU-specific flags
 ifneq ($(MCPU),)

base/binaryplatforms.jl

@@ -597,7 +597,7 @@ const arch_mapping = Dict(
     "armv7l" => "arm(v7l)?", # if we just see `arm-linux-gnueabihf`, we assume it's `armv7l`
     "armv6l" => "armv6l",
     "powerpc64le" => "p(ower)?pc64le",
-    "riscv64" => "riscv64",
+    "riscv64" => "(rv64|riscv64)",
 )
 # Keep this in sync with `CPUID.ISAs_by_family`
 # These are the CPUID side of the microarchitectures targeted by GCC flags in BinaryBuilder.jl
@@ -631,6 +631,9 @@ const arch_march_isa_mapping = let
             "a64fx" => get_set("aarch64", "a64fx"),
             "apple_m1" => get_set("aarch64", "apple_m1"),
         ],
+        "riscv64" => [
+            "riscv64" => get_set("riscv64", "riscv64")
+        ],
         "powerpc64le" => [
             "power8" => get_set("powerpc64le", "power8"),
         ],

base/cpuid.jl

@@ -61,6 +61,9 @@ const ISAs_by_family = Dict(
         "a64fx" => ISA(Set((JL_AArch64_v8_2a, JL_AArch64_lse, JL_AArch64_crc, JL_AArch64_rdm, JL_AArch64_sha2, JL_AArch64_ccpp, JL_AArch64_complxnum, JL_AArch64_fullfp16, JL_AArch64_sve))),
         "apple_m1" => ISA(Set((JL_AArch64_v8_5a, JL_AArch64_lse, JL_AArch64_crc, JL_AArch64_rdm, JL_AArch64_aes, JL_AArch64_sha2, JL_AArch64_sha3, JL_AArch64_ccpp, JL_AArch64_complxnum, JL_AArch64_fp16fml, JL_AArch64_fullfp16, JL_AArch64_dotprod, JL_AArch64_rcpc, JL_AArch64_altnzcv))),
     ],
+    "riscv64" => [
+        "riscv64" => ISA(Set{UInt32}()),
+    ],
     "powerpc64le" => [
         # We have no way to test powerpc64le features yet, so we're only going to declare the lowest ISA:
         "power8" => ISA(Set{UInt32}()),

cli/trampolines/trampolines_riscv64.S

@@ -0,0 +1,20 @@
+// This file is a part of Julia. License is MIT: https://julialang.org/license
+
+#include "common.h"
+#include "../../src/jl_exported_funcs.inc"
+
+#define SEP ;
+
+#define XX(name) \
+.global CNAME(name) SEP \
+.cfi_startproc SEP \
+.p2align    2 SEP \
+ CNAME(name)##: SEP \
+    auipc t3, %pcrel_hi(CNAMEADDR(name)) SEP \
+    ld t3, %pcrel_lo(CNAME(name))(t3) SEP \
+    jr t3 SEP \
+.cfi_endproc SEP \
+
+JL_RUNTIME_EXPORTED_FUNCS(XX)
+JL_CODEGEN_EXPORTED_FUNCS(XX)
+#undef XX

contrib/generate_precompile.jl

@@ -202,12 +202,15 @@ if Artifacts !== nothing
     using Artifacts, Base.BinaryPlatforms, Libdl
     artifacts_toml = abspath(joinpath(Sys.STDLIB, "Artifacts", "test", "Artifacts.toml"))
     artifact_hash("HelloWorldC", artifacts_toml)
-    oldpwd = pwd(); cd(dirname(artifacts_toml))
-    macroexpand(Main, :(@artifact_str("HelloWorldC")))
-    cd(oldpwd)
     artifacts = Artifacts.load_artifacts_toml(artifacts_toml)
     platforms = [Artifacts.unpack_platform(e, "HelloWorldC", artifacts_toml) for e in artifacts["HelloWorldC"]]
     best_platform = select_platform(Dict(p => triplet(p) for p in platforms))
+    if best_platform !== nothing
+      # @artifact errors for unsupported platforms
+      oldpwd = pwd(); cd(dirname(artifacts_toml))
+      macroexpand(Main, :(@artifact_str("HelloWorldC")))
+      cd(oldpwd)
+    end
     dlopen("libjulia$(Base.isdebugbuild() ? "-debug" : "")", RTLD_LAZY | RTLD_DEEPBIND)
     """
 end

contrib/normalize_triplet.py

@@ -14,6 +14,7 @@
     'i686': "i\\d86",
     'aarch64': "(arm|aarch)64",
     'armv7l': "arm(v7l)?",
+    'riscv64': "(rv64|riscv64)",
     'powerpc64le': "p(ower)?pc64le",
 }
 platform_mapping = {

doc/src/devdocs/build/build.md

@@ -148,6 +148,7 @@ Notes for various operating systems:
 Notes for various architectures:
 
 * [ARM](https://github.com/JuliaLang/julia/blob/master/doc/src/devdocs/build/arm.md)
+* [RISC-V](https://github.com/JuliaLang/julia/blob/master/doc/src/devdocs/build/riscv.md)
 
 ## Required Build Tools and External Libraries
 

doc/src/devdocs/build/riscv.md

@@ -0,0 +1,103 @@
+# RISC-V (Linux)
+
+Julia has experimental support for 64-bit RISC-V (RV64) processors running
+Linux. This file provides general guidelines for compilation, in addition to
+instructions for specific devices.
+
+A list of [known issues](https://github.com/JuliaLang/julia/labels/system:riscv)
+for RISC-V is available. If you encounter difficulties, please create an issue
+including the output from `cat /proc/cpuinfo`.
+
+
+## Compiling Julia
+
+For now, Julia will need to be compiled entirely from source, i.e., including
+all of its dependencies. This can be accomplished with the following
+`Make.user`:
+
+```make
+USE_BINARYBUILDER := 0
+```
+
+Additionally, it is required to indicate what architecture, and optionally which
+CPU to build for. This can be done by setting the `MARCH` and `MCPU` variables
+in `Make.user`
+
+The `MARCH` variable needs to be set to a RISC-V ISA string, which can be found by
+looking at the documentation of your device, or by inspecting `/proc/cpuinfo`. Only
+use flags that your compiler supports, e.g., run `gcc -march=help` to see a list of
+supported flags. A common value is `rv64gc`, which is a good starting point.
+
+The `MCPU` variable is optional, and can be used to further optimize the
+generated code for a specific CPU. If you are unsure, it is recommended to leave
+it unset. You can find a list of supported values by running `gcc --target-help`.
+
+For example, if you are using a StarFive VisionFive2, which contains a JH7110
+processor based on the SiFive U74, you can set these flags as follows:
+
+```make
+MARCH := rv64gc_zba_zbb
+MCPU := sifive-u74
+```
+
+If you prefer a portable build, you could use:
+
+```make
+MARCH := rv64gc
+
+# also set JULIA_CPU_TARGET to the expanded form of rv64gc
+# (it normally copies the value of MCPU, which we don't set)
+JULIA_CPU_TARGET := generic-rv64,i,m,a,f,d,zicsr,zifencei,c
+```
+
+### Cross-compilation
+
+A native build on a RISC-V device may take a very long time, so it's also
+possible to cross-compile Julia on a faster machine.
+
+First, get a hold of a RISC-V cross-compilation toolchain that provides
+support for C, C++ and Fortran. This can be done by checking-out the
+[riscv-gnu-toolchain](https://github.com/riscv-collab/riscv-gnu-toolchain)
+repository and building it as follows:
+
+```sh
+sudo mkdir /opt/riscv && sudo chown $USER /opt/riscv
+./configure --prefix=/opt/riscv --with-languages=c,c++,fortran
+make linux -j$(nproc)
+```
+
+Then, install the QEMU user-mode emulator for RISC-V, along with `binfmt`
+support to enable execution of RISC-V binaries on the host machine. The
+exact steps depend on your distribution, e.g., on Arch Linux it involves
+installing the `qemu-user-static` and `qemu-user-static-binfmt` packages.
+Note that to actually execute RISC-V binaries, QEMU will need to be able to
+find the RISC-V system root, which can be achieved by setting the
+`QEMU_LD_PREFIX` environment variable to the path of the root filesystem.
+
+Finally, compile Julia with the following `Make.user` variables (in addition to
+the ones from the previous section):
+
+```make
+XC_HOST=riscv64-unknown-linux-gnu
+OS=Linux
+export QEMU_LD_PREFIX=/opt/riscv/sysroot
+```
+
+Note that you will have to execute `make` with `PATH` set to include the
+cross-compilation toolchain, e.g., by running:
+
+```sh
+PATH=/opt/riscv/bin:$PATH make -j$(nproc)
+```
+
+Because of the RISC-V sysroot we use being very barren, you may need to
+add additional libraries that the Julia build system currently expects
+to be available system-wide. For example, the build currently relies on
+a system-provided `libz`, so you may need to copy this library from the
+Julia build into the system root:
+
+```sh
+make -C deps install-zlib
+cp -v usr/lib/libz.*   /opt/riscv/sysroot/usr/lib
+cp -v usr/include/z*.h /opt/riscv/sysroot/usr/include
+```