Get rid of inline assembly

asm.S

@@ -0,0 +1,89 @@
+/*
+    Entry point of all programs (_start).
+
+    It initializes DWARF call frame information, the stack pointer, the
+    frame pointer (needed for closures to work in start_rust) and the global
+    pointer. Then it calls _start_rust.
+*/
+
+.section .init, "ax"
+.global _start
+
+_start:
+    .cfi_startproc
+    .cfi_undefined ra
+
+    // .option push
+    // .option norelax
+    lui gp, %hi(__global_pointer$)
+    addi gp, gp, %lo(__global_pointer$)
+    // .option pop
+
+    lui sp, %hi(_stack_start)
+    addi sp, sp, %lo(_stack_start)
+
+    add s0, sp, zero
+
+    jal zero, _start_rust
+
+    .cfi_endproc
+
+
+/*
+    Trap entry point (_start_trap)
+
+    Saves caller saved registers ra, t0..6, a0..7, calls _start_trap_rust,
+    restores caller saved registers and then returns.
+*/
+.section .trap, "ax"
+.align 4
+.global _start_trap
+
+_start_trap:
+    addi sp, sp, -16*4
+
+    sw ra, 0*4(sp)
+    sw t0, 1*4(sp)
+    sw t1, 2*4(sp)
+    sw t2, 3*4(sp)
+    sw t3, 4*4(sp)
+    sw t4, 5*4(sp)
+    sw t5, 6*4(sp)
+    sw t6, 7*4(sp)
+    sw a0, 8*4(sp)
+    sw a1, 9*4(sp)
+    sw a2, 10*4(sp)
+    sw a3, 11*4(sp)
+    sw a4, 12*4(sp)
+    sw a5, 13*4(sp)
+    sw a6, 14*4(sp)
+    sw a7, 15*4(sp)
+
+    jal ra, _start_trap_rust
+
+    lw ra, 0*4(sp)
+    lw t0, 1*4(sp)
+    lw t1, 2*4(sp)
+    lw t2, 3*4(sp)
+    lw t3, 4*4(sp)
+    lw t4, 5*4(sp)
+    lw t5, 6*4(sp)
+    lw t6, 7*4(sp)
+    lw a0, 8*4(sp)
+    lw a1, 9*4(sp)
+    lw a2, 10*4(sp)
+    lw a3, 11*4(sp)
+    lw a4, 12*4(sp)
+    lw a5, 13*4(sp)
+    lw a6, 14*4(sp)
+    lw a7, 15*4(sp)
+
+    addi sp, sp, 16*4
+    mret
+
+
+/* Make sure there is an abort when linking */
+.section .init
+.globl abort
+abort:
+    jal zero, _start

assemble.sh

@@ -0,0 +1,14 @@
+#!/bin/bash
+
+set -euxo pipefail
+
+crate=riscv-rt
+
+# remove existing blobs because otherwise this will append object files to the old blobs
+rm -f bin/*.a
+
+riscv64-unknown-elf-gcc -c -mabi=ilp32 -march=rv32imac asm.S -o bin/$crate.o
+ar crs bin/riscv32imac-unknown-none-elf.a bin/$crate.o
+cp bin/riscv32imac-unknown-none-elf.a bin/riscv32imc-unknown-none-elf.a
+
+rm bin/$crate.o

build.rs

@@ -1,17 +1,30 @@
 // NOTE: Adapted from cortex-m/build.rs
 use std::env;
-use std::fs::File;
+use std::fs;
 use std::io::Write;
 use std::path::PathBuf;
 
 fn main() {
+    let target = env::var("TARGET").unwrap();
+    let out_dir = PathBuf::from(env::var("OUT_DIR").unwrap());
+    let name = env::var("CARGO_PKG_NAME").unwrap();
+
+    if target.starts_with("riscv") {
+        fs::copy(
+            format!("bin/{}.a", target),
+            out_dir.join(format!("lib{}.a", name)),
+        ).unwrap();
+
+        println!("cargo:rustc-link-lib=static={}", name);
+        println!("cargo:rustc-link-search={}", out_dir.display());
+    }
+
     // Put the linker script somewhere the linker can find it
-    let out = &PathBuf::from(env::var_os("OUT_DIR").unwrap());
-    File::create(out.join("link.x"))
+    fs::File::create(out_dir.join("link.x"))
         .unwrap()
         .write_all(include_bytes!("link.x"))
         .unwrap();
-    println!("cargo:rustc-link-search={}", out.display());
+    println!("cargo:rustc-link-search={}", out_dir.display());
 
     println!("cargo:rerun-if-changed=build.rs");
     println!("cargo:rerun-if-changed=link.x");

check-blobs.sh

@@ -0,0 +1,21 @@
+#!/bin/bash
+
+# Checks that the blobs are up to date with the committed assembly files
+
+set -euxo pipefail
+
+for lib in $(ls bin/*.a); do
+    filename=$(basename $lib)
+    riscv64-unknown-elf-objdump -Cd $lib > bin/${filename%.a}.before
+done
+
+./assemble.sh
+
+for lib in $(ls bin/*.a); do
+    filename=$(basename $lib)
+    riscv64-unknown-elf-objdump -Cd $lib > bin/${filename%.a}.after
+done
+
+for cksum in $(ls bin/*.after); do
+    diff -u $cksum ${cksum%.after}.before
+done

src/lib.rs

@@ -164,10 +164,8 @@
 #![no_std]
 #![deny(missing_docs)]
 #![deny(warnings)]
-#![feature(asm)]
 #![feature(compiler_builtins_lib)]
 #![feature(const_fn)]
-#![feature(global_asm)]
 #![feature(linkage)]
 
 extern crate riscv;
@@ -192,36 +190,6 @@ extern "C" {
 }
 
 
-/// Entry point of all programs (_start).
-///
-/// It initializes DWARF call frame information, the stack pointer, the
-/// frame pointer (needed for closures to work in start_rust) and the global
-/// pointer. Then it calls _start_rust.
-#[cfg(any(target_arch = "riscv32", target_arch = "riscv64"))]
-global_asm!(r#"
-.section .init, "ax"
-.globl _start
-_start:
-  .cfi_startproc
-  .cfi_undefined ra
-
-  // .option push
-  // .option norelax
-  lui gp, %hi(__global_pointer$)
-  addi gp, gp, %lo(__global_pointer$)
-  // .option pop
-
-  lui sp, %hi(_stack_start)
-  addi sp, sp, %lo(_stack_start)
-
-  add s0, sp, zero
-
-  jal zero, _start_rust
-
-  .cfi_endproc
-"#);
-
-
 /// Rust entry point (_start_rust)
 ///
 /// Zeros bss section, initializes data section and calls main. This function
@@ -275,60 +243,6 @@ macro_rules! entry {
 }
 
 
-/// Trap entry point (_start_trap)
-///
-/// Saves caller saved registers ra, t0..6, a0..7, calls _start_trap_rust,
-/// restores caller saved registers and then returns.
-#[cfg(any(target_arch = "riscv32", target_arch = "riscv64"))]
-global_asm!(r#"
-  .section .trap, "ax"
-  .align 4
-  .global _start_trap
-
-_start_trap:
-  addi sp, sp, -16*4
-
-  sw ra, 0*4(sp)
-  sw t0, 1*4(sp)
-  sw t1, 2*4(sp)
-  sw t2, 3*4(sp)
-  sw t3, 4*4(sp)
-  sw t4, 5*4(sp)
-  sw t5, 6*4(sp)
-  sw t6, 7*4(sp)
-  sw a0, 8*4(sp)
-  sw a1, 9*4(sp)
-  sw a2, 10*4(sp)
-  sw a3, 11*4(sp)
-  sw a4, 12*4(sp)
-  sw a5, 13*4(sp)
-  sw a6, 14*4(sp)
-  sw a7, 15*4(sp)
-
-  jal ra, _start_trap_rust
-
-  lw ra, 0*4(sp)
-  lw t0, 1*4(sp)
-  lw t1, 2*4(sp)
-  lw t2, 3*4(sp)
-  lw t3, 4*4(sp)
-  lw t4, 5*4(sp)
-  lw t5, 6*4(sp)
-  lw t6, 7*4(sp)
-  lw a0, 8*4(sp)
-  lw a1, 9*4(sp)
-  lw a2, 10*4(sp)
-  lw a3, 11*4(sp)
-  lw a4, 12*4(sp)
-  lw a5, 13*4(sp)
-  lw a6, 14*4(sp)
-  lw a7, 15*4(sp)
-
-  addi sp, sp, 16*4
-  mret
-"#);
-
-
 /// Trap entry point rust (_start_trap_rust)
 ///
 /// mcause is read to determine the cause of the trap. XLEN-1 bit indicates
@@ -351,12 +265,3 @@ pub extern "C" fn start_trap_rust() {
 #[no_mangle]
 #[linkage = "weak"]
 pub fn trap_handler(_: mcause::Trap) {}
-
-// Make sure there is an abort when linking
-#[cfg(any(target_arch = "riscv32", target_arch = "riscv64"))]
-global_asm!(r#"
-.section .init
-.globl abort
-abort:
-  jal zero, _start
-"#);