Merge branch 'master' into new_build

CHANGELOG.md

@@ -12,6 +12,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - New GitHub workflow for checking invalid labels in PRs
 - New GitHub workflow for checking modifications on CHANGELOG.md
 - New GitHub workflow for checking clippy lints in PRs
+- Optional cargo feature `single-hart` for single CPU targets
 
 ### Changed
 
@@ -20,6 +21,8 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - `start_trap_rust` is now marked as `unsafe`
 - Implement `r0` as inline assembly
 - Use `${ARCH_WIDTH}` in `link.x.in` to adapt to different archs
+- mhartid CSR is no longer read in single-hart mode, assumed zero
+- Ensure stack pointer is 16-byte aligned before jumping to Rust entry point
 
 ## [v0.11.0] - 2023-01-18
 

src/asm.rs

@@ -85,17 +85,16 @@ _abs_start:
     .option push
     .option norelax
     la gp, __global_pointer$
-    .option pop",
+    .option pop
+    // Allocate stacks",
     #[cfg(all(not(feature = "single-hart"), feature = "s-mode"))]
     "mv t2, a0 // the hartid is passed as parameter by SMODE",
     #[cfg(all(not(feature = "single-hart"), not(feature = "s-mode")))]
     "csrr t2, mhartid",
     #[cfg(not(feature = "single-hart"))]
     "lui t0, %hi(_max_hart_id)
     add t0, t0, %lo(_max_hart_id)
-    bgtu t2, t0, abort",
-    "// Allocate stacks
-    la sp, _stack_start
+    bgtu t2, t0, abort
     lui t0, %hi(_hart_stack_size)
     add t0, t0, %lo(_hart_stack_size)",
     #[cfg(all(not(feature = "single-hart"), riscvm))]
@@ -109,8 +108,10 @@ _abs_start:
     addi t1, t1, -1
     bnez t1, 1b
 2:  ",
-    "sub sp, sp, t0
-
+    "la t1, _stack_start",
+    #[cfg(not(feature = "single-hart"))]
+    "sub t1, t1, t0",
+    "andi sp, t1, -16 // Force 16-byte alignment
     // Set frame pointer
     add s0, sp, zero
 
@@ -135,6 +136,8 @@ _abs_start:
 #[rustfmt::skip]
 macro_rules! trap_handler {
     ($STORE:ident, $LOAD:ident, $BYTES:literal, $TRAP_SIZE:literal, [$(($REG:ident, $LOCATION:literal)),*]) => {
+        // ensure we do not break that sp is 16-byte aligned
+        const _: () = assert!(($TRAP_SIZE * $BYTES) % 16 == 0);
         global_asm!(
         "
             .section .trap, \"ax\"

src/lib.rs

@@ -327,7 +327,7 @@
 //!
 //! ## `single-hart`
 //!
-//! This feature saves a little code size by removing unnecessary stack space calculation if there is only one hart on the target.
+//! This feature saves a little code size if there is only one hart on the target.
 //!
 //! ## `s-mode`
 //!
@@ -372,7 +372,10 @@ use core::sync::atomic::{compiler_fence, Ordering};
 use riscv::register::{scause as xcause, stvec as xtvec, stvec::TrapMode as xTrapMode};
 
 #[cfg(not(feature = "s-mode"))]
-use riscv::register::{mcause as xcause, mhartid, mtvec as xtvec, mtvec::TrapMode as xTrapMode};
+use riscv::register::{mcause as xcause, mtvec as xtvec, mtvec::TrapMode as xTrapMode};
+
+#[cfg(all(not(feature = "single-hart"), not(feature = "s-mode")))]
+use riscv::register::mhartid;
 
 pub use riscv_rt_macros::{entry, pre_init};
 
@@ -404,13 +407,20 @@ pub unsafe extern "C" fn start_rust(a0: usize, a1: usize, a2: usize) -> ! {
         fn _mp_hook(hartid: usize) -> bool;
     }
 
-    // sbi passes hartid as first parameter (a0)
-    #[cfg(feature = "s-mode")]
-    let hartid = a0;
-    #[cfg(not(feature = "s-mode"))]
-    let hartid = mhartid::read();
+    #[cfg(not(feature = "single-hart"))]
+    let run_init = {
+        // sbi passes hartid as first parameter (a0)
+        #[cfg(feature = "s-mode")]
+        let hartid = a0;
+        #[cfg(not(feature = "s-mode"))]
+        let hartid = mhartid::read();
+
+        _mp_hook(hartid)
+    };
+    #[cfg(feature = "single-hart")]
+    let run_init = true;
 
-    if _mp_hook(hartid) {
+    if run_init {
         __pre_init();
 
         // Initialize RAM
@@ -661,6 +671,7 @@ pub unsafe extern "Rust" fn default_pre_init() {}
 #[doc(hidden)]
 #[no_mangle]
 #[rustfmt::skip]
+#[cfg(not(feature = "single-hart"))]
 pub extern "Rust" fn default_mp_hook(hartid: usize) -> bool {
     match hartid {
         0 => true,