Possibly wrong argc/argv

[blckngm]

Rust contracts built by capsule build (esp. in non-release build) may not get the correct argc and argv arguments because the compiler may insert function prologue before our assembly code in _start and change the sp register.

One possible solution is to mark the _start function #[naked].

Or the _start function can be written in pure assembly and linked with rust code.

(By the way the program_entry function should use extern "C" so that it has a defined calling convention.)

[blckngm]

#[no_mangle]
#[naked]
pub unsafe extern "C" fn _start() -> ! {
    core::arch::asm!(
        "lw a0, 0(sp)",
        "addi a1, sp, 8",
        "call main",
        "li a7, 93",
        "ecall",
        options(noreturn)
    );
}

#[no_mangle]
extern "C" fn main(_argc: u64, _argv: *const *const u8) -> i8 {
    _argc as i8
}

[XuJiandong]

Use the code snippets below to work with argc and argv:

https://github.com/XuJiandong/rvv-testcases/blob/76944bc7a6d1e87c2e3d171f361881b92b1db9ff/cases/src/main.rs#L64-L81

[blckngm]

Global asm also works, and does not require any nightly features:

core::arch::global_asm!(
    ".global _start",
    "_start:",
    "lw a0, 0(sp)",
    "addi a1, sp, 8",
    "call main",
    "li a7, 93",
    "ecall",
);