Closed
Description
I tried this code:
#![no_std]
#![no_main]
#![feature(asm)]
#![feature(lang_items)]
///! A small reproduction case
///!
///! Build with `cargo build`
///!
///! Notes:
///! - setting opt-level to 0 or 1 compiles
///! - opt-level 2, 3, "s", "z" cause the error
///! - a release build works just fine, just a debug build with optimization has the issue
use core::mem::{ManuallyDrop, MaybeUninit};
use core::panic::PanicInfo;
pub unsafe fn call_with_stack<T>(
arg: &mut T,
function: extern "sysv64" fn(&mut T) -> (),
stack: *mut u8,
) {
asm!(r#"
mov rbp, rsp
mov rsp, $2
call $1
mov rsp, rbp
"#
: // Return values
: "{rdi}"(arg), "r"(function), "r"(stack) // Arguments
: "rbp", "cc", "memory" // Clobbers
: "volatile", "intel" // Options
);
}
/// Calls a closure and returns the result
///
/// This function is unsafe because it changes the stack pointer to stack.
/// stack must be suitable to be used as a stack pointer on the target system.
pub unsafe fn call_closure_with_stack<F, R>(closure: F, stack: *mut u8) -> R
where
F: FnOnce() -> R,
{
extern "sysv64" fn inner<F, R>(data: &mut (ManuallyDrop<F>, MaybeUninit<R>))
where
F: FnOnce() -> R,
{
let result = {
// Read the closure from context, taking ownership of it
let function = unsafe { ManuallyDrop::take(&mut data.0) };
// Call the closure.
// This consumes it and returns the result
function()
};
// Write the result into the context
data.1 = MaybeUninit::new(result);
}
// The context contains the closure and uninitialized memory for the return value
let mut context = (ManuallyDrop::new(closure), MaybeUninit::uninit());
call_with_stack(
&mut context,
// We create a new, internal function that does not close over anything
// and takes a context reference as its argument
inner,
stack,
);
// Read the result from the context
// No values are in the context anymore afterwards
context.1.assume_init()
}
#[no_mangle]
pub unsafe fn _start(stack: *mut u8) {
call_closure_with_stack(|| (), stack);
}
#[no_mangle]
pub unsafe fn efi_main(stack: *mut u8) {
call_closure_with_stack(|| (), stack);
}
#[panic_handler]
fn panic(_info: &PanicInfo) -> ! {
loop {}
}
#[lang = "eh_personality"] extern fn eh_personality() {}I expected to see this happen:
The inline assembly should be compiled in intel syntax
Instead, this happened:
Under some circumstances, Rust seems to forget about the intel attribute and tries to compile it as AT&T assembly.
I have not found a consistent reason for this, if the code compiles or not changes seemingly at random with different compile options or code reordering.
Removing call_closure_with_stack also made resulted in no error, but I am not sure if it is the cause or just massages the code in such a way that the issue goes silent.
full cargo error message with --verbose
Compiling asm_test v0.1.0 (C:\Users\Dario\RustProjects\asm_test)
Running `rustc --crate-name asm_test --edition=2018 'src\main.rs' --error-format=json --json=diagnostic-rendered-ansi --crate-type bin --emit=dep-info,link -C opt-level=s -C debuginfo=2 -C debug-assertions=on -C metadata=ff8ce8b6214d71b9 --out-dir 'C:\Users\Dario\RustProjects\asm_test\target\debug\deps' -C 'incremental=C:\Users\Dario\RustProjects\asm_test\target\debug\incremental' -L 'dependency=C:\Users\Dario\RustProjects\asm_test\target\debug\deps' -Ctarget-feature=+crt-static`
error: <inline asm>:2:5: error: unknown use of instruction mnemonic without a size suffix
mov rbp, rsp
^
--> src\main.rs:23:5
|
23 | / asm!(r#"
24 | | mov rbp, rsp
25 | | mov rsp, $2
26 | |
... |
34 | | : "volatile", "intel" // Options
35 | | );
| |______^
error: <inline asm>:5:5: error: unknown use of instruction mnemonic without a size suffix
call %rax
^
--> src\main.rs:23:5
|
23 | / asm!(r#"
24 | | mov rbp, rsp
25 | | mov rsp, $2
26 | |
... |
34 | | : "volatile", "intel" // Options
35 | | );
| |______^
error: <inline asm>:7:5: error: unknown use of instruction mnemonic without a size suffix
mov rsp, rbp
^
--> src\main.rs:23:5
|
23 | / asm!(r#"
24 | | mov rbp, rsp
25 | | mov rsp, $2
26 | |
... |
34 | | : "volatile", "intel" // Options
35 | | );
| |______^
error: aborting due to 3 previous errors
error: could not compile `asm_test`.
Caused by:
process didn't exit successfully: `rustc --crate-name asm_test --edition=2018 'src\main.rs' --error-format=json --json=diagnostic-rendered-ansi --crate-type bin --emit=dep-info,link -C opt-level=s -C debuginfo=2 -C debug-assertions=on -C metadata=ff8ce8b6214d71b9 --out-dir 'C:\Users\Dario\RustProjects\asm_test\target\debug\deps' -C 'incremental=C:\Users\Dario\RustProjects\asm_test\target\debug\incremental' -L 'dependency=C:\Users\Dario\RustProjects\asm_test\target\debug\deps' -Ctarget-feature=+crt-static` (exit code: 1)
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rustc --version --verbose:
Windows:
rustc 1.44.0-nightly (f509b26a7 2020-03-18)
binary: rustc
commit-hash: f509b26a7730d721ef87423a72b3fdf8724b4afa
commit-date: 2020-03-18
host: x86_64-pc-windows-msvc
release: 1.44.0-nightly
LLVM version: 9.0
Linux:
rustc 1.44.0-nightly (f509b26a7 2020-03-18)
binary: rustc
commit-hash: f509b26a7730d721ef87423a72b3fdf8724b4afa
commit-date: 2020-03-18
host: x86_64-unknown-linux-gnu
release: 1.44.0-nightly
LLVM version: 9.0