Add rust standard library support for risc0 zkvm.

compiler/rustc_target/src/spec/mod.rs

@@ -981,6 +981,7 @@ supported_targets! {
 
     ("riscv32i-unknown-none-elf", riscv32i_unknown_none_elf),
     ("riscv32im-unknown-none-elf", riscv32im_unknown_none_elf),
+    ("riscv32im-risc0-zkvm-elf", riscv32im_risc0_zkvm_elf),
     ("riscv32imc-unknown-none-elf", riscv32imc_unknown_none_elf),
     ("riscv32imc-esp-espidf", riscv32imc_esp_espidf),
     ("riscv32imac-unknown-none-elf", riscv32imac_unknown_none_elf),

compiler/rustc_target/src/spec/riscv32im_risc0_zkvm_elf.rs

@@ -0,0 +1,36 @@
+use crate::spec::{LinkerFlavor, LldFlavor, PanicStrategy, RelocModel};
+use crate::spec::{Target, TargetOptions};
+
+pub fn target() -> Target {
+    Target {
+        data_layout: "e-m:e-p:32:32-i64:64-n32-S128".into(),
+        llvm_target: "riscv32".into(),
+        pointer_width: 32,
+        arch: "riscv32".into(),
+
+        options: TargetOptions {
+            os: "zkvm".into(),
+            vendor: "risc0".into(),
+            linker_flavor: LinkerFlavor::Lld(LldFlavor::Ld),
+            linker: Some("rust-lld".into()),
+            cpu: "generic-rv32".into(),
+
+            // Some crates (*cough* crossbeam) assume you have 64 bit
+            // atomics if the target name is not in a hardcoded list.
+            // Since zkvm is singlethreaded and all operations are
+            // atomic, I guess we can just say we support 64-bit
+            // atomics.
+            max_atomic_width: Some(64),
+            atomic_cas: true,
+
+            features: "+m".into(),
+            executables: true,
+            panic_strategy: PanicStrategy::Abort,
+            relocation_model: RelocModel::Static,
+            emit_debug_gdb_scripts: false,
+            eh_frame_header: false,
+            singlethread: true,
+            ..Default::default()
+        },
+    }
+}

library/std/Cargo.toml

@@ -48,7 +48,7 @@ hermit-abi = { version = "0.2.0", features = ['rustc-dep-of-std'] }
 wasi = { version = "0.11.0", features = ['rustc-dep-of-std'], default-features = false }
 
 [target.'cfg(target_os = "zkvm")'.dependencies]
-risc0-zkvm-platform = { version = "0.10.0", default-features = false, features = ['rustc-dep-of-std'] }
+risc0-zkvm-platform = { git = "https://github.com/risc0/risc0", default-features = false, features = ['rustc-dep-of-std'] }
 
 [features]
 backtrace = [

library/std/build.rs

@@ -29,6 +29,7 @@ fn main() {
         || target.contains("asmjs")
         || target.contains("espidf")
         || target.contains("solid")
+        || target.contains("zkvm")
     {
         // These platforms don't have any special requirements.
     } else {

library/std/src/sys/common/alloc.rs

@@ -14,7 +14,7 @@ use crate::ptr;
     target_arch = "asmjs",
     target_arch = "wasm32",
     target_arch = "hexagon",
-    all(target_arch = "riscv32", not(target_os = "espidf")),
+    all(target_arch = "riscv32", not(any(target_os = "espidf", target_os = "zkvm"))),
     all(target_arch = "xtensa", not(target_os = "espidf")),
 )))]
 pub const MIN_ALIGN: usize = 8;
@@ -28,9 +28,9 @@ pub const MIN_ALIGN: usize = 8;
     target_arch = "wasm64",
 )))]
 pub const MIN_ALIGN: usize = 16;
-// The allocator on the esp-idf platform guarantees 4 byte alignment.
+// The allocator on the esp-idf and zkvm platforms guarantee 4 byte alignment.
 #[cfg(all(any(
-    all(target_arch = "riscv32", target_os = "espidf"),
+    all(target_arch = "riscv32", any(target_os = "espidf", target_os = "zkvm")),
     all(target_arch = "xtensa", target_os = "espidf"),
 )))]
 pub const MIN_ALIGN: usize = 4;

library/std/src/sys/zkvm/stdio.rs

@@ -58,6 +58,6 @@ pub fn is_ebadf(_err: &io::Error) -> bool {
     true
 }
 
-pub fn panic_output() -> Option<Vec<u8>> {
+pub fn panic_output() -> Option<impl io::Write> {
     Some(Stderr::new())
 }

library/std/src/sys_common/mod.rs

@@ -40,6 +40,7 @@ pub mod wtf8;
 cfg_if::cfg_if! {
     if #[cfg(any(target_os = "l4re",
                  target_os = "hermit",
+                 target_os = "zkvm",
                  feature = "restricted-std",
                  all(target_family = "wasm", not(target_os = "emscripten")),
                  all(target_vendor = "fortanix", target_env = "sgx")))] {

src/bootstrap/lib.rs

@@ -206,7 +206,7 @@ const EXTRA_CHECK_CFGS: &[(Option<Mode>, &'static str, Option<&[&'static str]>)]
     (Some(Mode::Std), "backtrace_in_libstd", None),
     /* Extra values not defined in the built-in targets yet, but used in std */
     (Some(Mode::Std), "target_env", Some(&["libnx"])),
-    (Some(Mode::Std), "target_os", Some(&["watchos"])),
+    (Some(Mode::Std), "target_os", Some(&["watchos", "zkvm"])),
     (
         Some(Mode::Std),
         "target_arch",
@@ -761,6 +761,11 @@ impl Build {
         if self.config.profiler_enabled(target) {
             features.push_str(" profiler");
         }
+        // Generate memcpy, etc.  FIXME: Remove this once compiler-builtins
+        // automatically detects this target.
+        if target.contains("zkvm") {
+            features.push_str(" compiler-builtins-mem");
+        }
         features
     }
 

src/doc/rustc/src/platform-support.md

@@ -274,6 +274,7 @@ target | std | host | notes
 `powerpc64le-unknown-linux-musl` | ? |  |
 `riscv32gc-unknown-linux-gnu` |   |   | RISC-V Linux (kernel 5.4, glibc 2.33)
 `riscv32gc-unknown-linux-musl` |   |   | RISC-V Linux (kernel 5.4, musl + RISCV32 support patches)
+`riscv32im-risc0-zkvm-elf` | * |  | Risc-V running on the Risc0 Zero-Knowledge Virtual Machine
 `riscv32im-unknown-none-elf` | * |  | Bare RISC-V (RV32IM ISA)
 [`riscv32imac-unknown-xous-elf`](platform-support/riscv32imac-unknown-xous-elf.md) | ? |  | RISC-V Xous (RV32IMAC ISA)
 `riscv32imc-esp-espidf` | ✓ |  | RISC-V ESP-IDF

src/test/ui/check-cfg/well-known-values.stderr

@@ -7,7 +7,7 @@ LL | #[cfg(target_os = "linuz")]
    |                   help: did you mean: `"linux"`
    |
    = note: `#[warn(unexpected_cfgs)]` on by default
-   = note: expected values for `target_os` are: android, cuda, dragonfly, emscripten, espidf, freebsd, fuchsia, haiku, hermit, horizon, illumos, ios, l4re, linux, macos, netbsd, none, openbsd, psp, redox, solaris, solid_asp3, tvos, uefi, unknown, vxworks, wasi, windows, xous
+   = note: expected values for `target_os` are: android, cuda, dragonfly, emscripten, espidf, freebsd, fuchsia, haiku, hermit, horizon, illumos, ios, l4re, linux, macos, netbsd, none, openbsd, psp, redox, solaris, solid_asp3, tvos, uefi, unknown, vxworks, wasi, windows, xous, zkvm
 
 warning: unexpected `cfg` condition value
   --> $DIR/well-known-values.rs:14:7

src/tools/build-manifest/src/main.rs

@@ -117,6 +117,7 @@ static TARGETS: &[&str] = &[
     "powerpc64-unknown-linux-gnu",
     "powerpc64le-unknown-linux-gnu",
     "riscv32i-unknown-none-elf",
+    "riscv32im-risc0-zkvm-elf",
     "riscv32im-unknown-none-elf",
     "riscv32imc-unknown-none-elf",
     "riscv32imac-unknown-none-elf",