More standard library functions (#784)

More standard library functions for sproll.

Works with scroll-tech/sproll-evm#65

ceno_rt/Cargo.toml

@@ -10,4 +10,5 @@ repository = "https://github.com/scroll-tech/ceno"
 version = "0.1.0"
 
 [dependencies]
+getrandom = { version = "*", features = ["custom"], default-features = false }
 rkyv = { version = "0.8", features = ["pointer_width_32"] }

ceno_rt/src/lib.rs

@@ -1,6 +1,7 @@
 #![deny(clippy::cargo)]
 #![feature(strict_overflow_ops)]
 #![feature(linkage)]
+use getrandom::{Error, register_custom_getrandom};
 
 #[cfg(target_arch = "riscv32")]
 use core::arch::{asm, global_asm};
@@ -23,6 +24,18 @@ pub extern "C" fn sys_write(_fd: i32, _buf: *const u8, _count: usize) -> isize {
     unimplemented!();
 }
 
+#[no_mangle]
+#[linkage = "weak"]
+pub extern "C" fn sys_alloc_words(_nwords: usize) -> *mut u32 {
+    unimplemented!();
+}
+
+#[no_mangle]
+#[linkage = "weak"]
+pub extern "C" fn sys_getenv(_name: *const u8) -> *const u8 {
+    unimplemented!();
+}
+
 /// Generates random bytes.
 ///
 /// # Safety
@@ -51,6 +64,18 @@ pub unsafe extern "C" fn sys_rand(recv_buf: *mut u8, words: usize) {
     }
 }
 
+/// Custom random number generator for getrandom
+///
+/// One of sproll's dependencies uses the getrandom crate,
+/// and it will only build, if we provide a custom random number generator.
+///
+/// Otherwise, it'll complain about an unsupported target.
+pub fn my_get_random(buf: &mut [u8]) -> Result<(), Error> {
+    unsafe { sys_rand(buf.as_mut_ptr(), buf.len()) };
+    Ok(())
+}
+register_custom_getrandom!(my_get_random);
+
 pub fn halt(exit_code: u32) -> ! {
     #[cfg(target_arch = "riscv32")]
     unsafe {