riscv-macros: Move entry attribute macro

riscv-macros/CHANGELOG.md

@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 ### Added
 
+- `entry` macro for the `riscv-rt` crate (migrated from `riscv-rt-macros`).
 - `post_init` macro for the `riscv-rt` crate (migrated from `riscv-rt-macros`).
 
 ## v0.4.0 - 2025-12-19

riscv-macros/Cargo.toml

@@ -19,6 +19,7 @@ proc-macro = true
 rt = []
 rt-v-trap = ["rt"]
 riscv-rt = ["rt", "syn/extra-traits", "syn/full"]
+u-boot = []
 
 [dependencies]
 proc-macro2 = "1.0"

riscv-macros/src/lib.rs

@@ -90,3 +90,48 @@ pub fn pac_enum(attr: TokenStream, item: TokenStream) -> TokenStream {
 pub fn post_init(args: TokenStream, input: TokenStream) -> TokenStream {
     riscv_rt::Fn::post_init(args, input)
 }
+
+/// Attribute to declare the entry point of the program
+///
+/// The specified function will be called by the reset handler *after* RAM has been initialized.
+/// If present, the FPU will also be enabled before the function is called.
+///
+/// # Signature
+///
+/// ## Regular Usage
+///
+/// The type of the specified function must be `[unsafe] fn([usize[, usize[, usize]]]) -> !` (never ending function).
+/// The optional arguments correspond to the values passed in registers `a0`, `a1`, and `a2`.
+/// The first argument holds the hart ID of the current hart, which is useful for multi-hart systems.
+/// The other two arguments are currently unused and reserved for future use.
+///
+/// ## With U-Boot
+///
+/// This runtime supports being booted by U-Boot. In this case, the entry point function
+/// must have the signature `[unsafe] fn([c_int[, *const *const c_char]]) -> !`, where the first argument
+/// corresponds to the `argc` parameter and the second argument corresponds to the `argv` parameter passed by U-Boot.
+///
+/// Remember to enable the `u-boot` feature in the `riscv-rt` crate to use this functionality.
+///
+/// # IMPORTANT
+///
+/// This attribute can appear at most *once* in the dependency graph.
+///
+/// The entry point will be called by the reset handler. The program can't reference to the entry
+/// point, much less invoke it.
+///
+/// # Examples
+///
+/// ``` no_run
+/// #[riscv_macros::entry]
+/// fn main() -> ! {
+///     loop {
+///         /* .. */
+///     }
+/// }
+/// ```
+#[cfg(feature = "riscv-rt")]
+#[proc_macro_attribute]
+pub fn entry(args: TokenStream, input: TokenStream) -> TokenStream {
+    riscv_rt::Fn::entry(args, input)
+}

riscv-macros/src/riscv_rt.rs

@@ -8,10 +8,19 @@ use syn::{
 
 /// Enum representing the supported runtime function attributes
 pub enum Fn {
+    Entry,
     PostInit,
 }
 
 impl Fn {
+    /// Convenience method to generate the token stream for the `entry` attribute
+    pub fn entry(args: TokenStream, input: TokenStream) -> TokenStream {
+        match Self::Entry.check_args_empty(args) {
+            Ok(_) => Self::Entry.quote_fn(input),
+            Err(e) => e.to_compile_error().into(),
+        }
+    }
+
     /// Convenience method to generate the token stream for the `post_init` attribute
     pub fn post_init(args: TokenStream, input: TokenStream) -> TokenStream {
         match Self::PostInit.check_args_empty(args) {
@@ -83,6 +92,7 @@ impl Fn {
     const fn attr_name(&self) -> &'static str {
         // Use this match to specify attribute names for different functions in the future
         match self {
+            Self::Entry => "entry",
             Self::PostInit => "post_init",
         }
     }
@@ -91,6 +101,10 @@ impl Fn {
     const fn expected_signature(&self) -> &'static str {
         // Use this match to specify expected signatures for different functions in the future
         match self {
+            #[cfg(not(feature = "u-boot"))]
+            Self::Entry => "[unsafe] fn([usize[, usize[, usize]]]) -> !",
+            #[cfg(feature = "u-boot")]
+            Self::Entry => "[unsafe] fn([c_int[, *const *const c_char]]) -> !",
             Self::PostInit => "[unsafe] fn([usize])",
         }
     }
@@ -99,6 +113,10 @@ impl Fn {
     fn check_inputs(&self, inputs: &Punctuated<FnArg, Comma>) -> Result<()> {
         // Use this match to specify expected input arguments for different functions in the future
         match self {
+            #[cfg(not(feature = "u-boot"))]
+            Self::Entry => self.check_fn_args(inputs, &["usize", "usize", "usize"]),
+            #[cfg(feature = "u-boot")]
+            Self::Entry => self.check_fn_args(inputs, &["c_int", "*const *const c_char"]),
             Self::PostInit => self.check_fn_args(inputs, &["usize"]),
         }
     }
@@ -107,6 +125,7 @@ impl Fn {
     fn check_output(&self, output: &ReturnType) -> Result<()> {
         // Use this match to specify expected output types for different functions in the future
         match self {
+            Self::Entry => check_output_never(output),
             Self::PostInit => check_output_empty(output),
         }
     }
@@ -115,6 +134,7 @@ impl Fn {
     fn export_name(&self, _f: &ItemFn) -> Option<TokenStream2> {
         // Use this match to specify export names for different functions in the future
         let export_name = match self {
+            Self::Entry => Some("main".to_string()),
             Self::PostInit => Some("__post_init".to_string()),
         };
 
@@ -129,7 +149,7 @@ impl Fn {
     fn link_section(&self, _f: &ItemFn) -> Option<TokenStream2> {
         // Use this match to specify section names for different functions in the future
         let section_name: Option<String> = match self {
-            Self::PostInit => None,
+            Self::Entry | Self::PostInit => None,
         };
 
         section_name.map(|section| quote! {
@@ -236,3 +256,14 @@ fn check_output_empty(output: &ReturnType) -> Result<()> {
         },
     }
 }
+
+/// Make sure the output type is `!` (never)
+fn check_output_never(output: &ReturnType) -> Result<()> {
+    match output {
+        ReturnType::Type(_, ty) => match **ty {
+            Type::Never(_) => Ok(()),
+            _ => Err(Error::new(ty.span(), "return type must be !")),
+        },
+        ReturnType::Default => Err(Error::new(output.span(), "return type must be !")),
+    }
+}

riscv-rt/CHANGELOG.md

@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 ### Changed
 
+- Using `entry` from `riscv-macros` instead of `riscv-rt-macros`.
 - Using `post_init` from `riscv-macros` instead of `riscv-rt-macros`.
 
 ## v0.17.1 - 2026-01-13

riscv-rt/Cargo.toml

@@ -42,7 +42,7 @@ post-init = []
 s-mode = ["riscv-rt-macros/s-mode"]
 single-hart = []
 v-trap = ["riscv-rt-macros/v-trap", "riscv/rt-v-trap", "riscv-macros/rt-v-trap"]
-u-boot = ["riscv-rt-macros/u-boot", "single-hart"]
+u-boot = ["riscv-rt-macros/u-boot", "single-hart", "riscv-macros/u-boot"]
 no-interrupts = []
 no-exceptions = []
 no-mhartid = ["single-hart"]

riscv-rt/src/lib.rs

@@ -699,7 +699,8 @@ use riscv::register::{
     mtvec::{self as xtvec, Mtvec as Xtvec, TrapMode},
 };
 
-pub use riscv_rt_macros::{core_interrupt, entry, exception, external_interrupt};
+pub use riscv_macros::entry;
+pub use riscv_rt_macros::{core_interrupt, exception, external_interrupt};
 pub use riscv_types::*;
 
 #[cfg(feature = "post-init")]

tests-trybuild/tests/riscv-rt/entry/fail_arg_count.rs

@@ -0,0 +1,4 @@
+#[riscv_rt::entry]
+fn entry_point(_hart_id: usize, _dtb: usize, _other: usize, _one_more: usize) {}
+
+fn main() {}

tests-trybuild/tests/riscv-rt/entry/fail_arg_count.stderr

@@ -0,0 +1,5 @@
+error: `#[entry]` function has too many input arguments
+ --> tests/riscv-rt/entry/fail_arg_count.rs:2:61
+  |
+2 | fn entry_point(_hart_id: usize, _dtb: usize, _other: usize, _one_more: usize) {}
+  |                                                             ^^^^^^^^^

tests-trybuild/tests/riscv-rt/entry/fail_arg_type.rs

@@ -0,0 +1,4 @@
+#[riscv_rt::entry]
+fn entry_point(_hart_id: String) {}
+
+fn main() {}

tests-trybuild/tests/riscv-rt/entry/fail_arg_type.stderr

@@ -0,0 +1,5 @@
+error: argument type must be usize
+ --> tests/riscv-rt/entry/fail_arg_type.rs:2:26
+  |
+2 | fn entry_point(_hart_id: String) {}
+  |                          ^^^^^^

tests-trybuild/tests/riscv-rt/entry/fail_async.rs

@@ -0,0 +1,4 @@
+#[riscv_rt::entry]
+async fn entry_point() {}
+
+fn main() {}

tests-trybuild/tests/riscv-rt/entry/fail_async.stderr

@@ -0,0 +1,5 @@
+error: `#[entry]` function signature must be `[unsafe] fn([usize[, usize[, usize]]]) -> !`
+ --> tests/riscv-rt/entry/fail_async.rs:2:1
+  |
+2 | async fn entry_point() {}
+  | ^^^^^

tests-trybuild/tests/riscv-rt/entry/fail_public.rs

@@ -0,0 +1,4 @@
+#[riscv_rt::entry]
+pub fn entry_point() -> ! {}
+
+fn main() {}

tests-trybuild/tests/riscv-rt/entry/fail_public.stderr

@@ -0,0 +1,5 @@
+error: `#[entry]` function must be private
+ --> tests/riscv-rt/entry/fail_public.rs:2:1
+  |
+2 | pub fn entry_point() -> ! {}
+  | ^^^

tests-trybuild/tests/riscv-rt/entry/fail_return_empty.rs

@@ -0,0 +1,4 @@
+#[riscv_rt::entry]
+fn entry_point() {}
+
+fn main() {}

tests-trybuild/tests/riscv-rt/entry/fail_return_empty.stderr

@@ -0,0 +1,7 @@
+error: return type must be !
+ --> tests/riscv-rt/entry/fail_return_empty.rs:1:1
+  |
+1 | #[riscv_rt::entry]
+  | ^^^^^^^^^^^^^^^^^^
+  |
+  = note: this error originates in the attribute macro `riscv_rt::entry` (in Nightly builds, run with -Z macro-backtrace for more info)

tests-trybuild/tests/riscv-rt/entry/fail_return_tuple.rs

@@ -0,0 +1,4 @@
+#[riscv_rt::entry]
+fn entry_point() -> () {}
+
+fn main() {}

tests-trybuild/tests/riscv-rt/entry/fail_return_tuple.stderr

@@ -0,0 +1,5 @@
+error: return type must be !
+ --> tests/riscv-rt/entry/fail_return_tuple.rs:2:21
+  |
+2 | fn entry_point() -> () {}
+  |                     ^^

tests-trybuild/tests/riscv-rt/entry/pass_safe.rs

@@ -0,0 +1,6 @@
+#[riscv_rt::entry]
+fn entry_point(_hart_id: usize) -> ! {
+    loop {}
+}
+
+fn main() {} // TEST OK

tests-trybuild/tests/riscv-rt/entry/pass_unsafe.rs

@@ -0,0 +1,6 @@
+#[riscv_rt::entry]
+unsafe fn entry_point(_hart_id: usize) -> ! {
+    loop {}
+}
+
+fn main() {} // TEST OK