proc_syscall/
lib.rs

1use convert_case::{Case, Casing};
2use proc_macro::TokenStream;
3use quote::{format_ident, quote, TokenStreamExt};
4use syn::{parse_macro_input, punctuated::Punctuated, token::Comma, BareFnArg, ReturnType, Type};
5
6const X64_ARG_REGS: [&str; 6] = ["rdi", "rsi", "rdx", "r10", "r8", "r9"];
7
8#[proc_macro_attribute]
9pub fn syscall(attr: TokenStream, item: TokenStream) -> TokenStream {
10    let item_type = parse_macro_input!(item as syn::ItemType);
11
12    let bare_fn = match *item_type.ty.clone() {
13        syn::Type::BareFn(bare_fn) => bare_fn,
14        _ => {
15            panic!("Must be a fn type eg. fn(input: usize) -> usize");
16        }
17    };
18
19    let inputs = bare_fn.inputs;
20    if inputs.len() > 6 {
21        panic!("A syscall has a maximum of six arguments")
22    }
23
24    let vis = item_type.vis;
25    let fn_name = format_ident!("{}", item_type.ident.to_string().to_case(Case::Snake));
26    let return_type = bare_fn.output;
27
28    let never_return = never_returns(&return_type);
29
30    let x86_64_asm_tokens = x86_64_asm_tokens(&inputs, never_return);
31    let sys_num = proc_macro2::TokenStream::from(attr);
32
33    let tokens = if never_return {
34        quote! {
35            #[inline(always)]
36            #[cfg(target_arch = "x86_64")]
37            #vis unsafe fn #fn_name(#inputs) #return_type {
38                let rax = #sys_num;
39                #x86_64_asm_tokens
40            }
41        }
42    } else {
43        quote! {
44            #[inline(always)]
45            #[cfg(target_arch = "x86_64")]
46            #vis unsafe fn #fn_name(#inputs) #return_type {
47                let mut rax = #sys_num as _;
48                #x86_64_asm_tokens
49                rax
50            }
51        }
52    };
53
54    TokenStream::from(tokens)
55}
56
57fn never_returns(return_type: &syn::ReturnType) -> bool {
58    match &return_type {
59        ReturnType::Default => false,
60        ReturnType::Type(_, ty) => matches!(ty.as_ref(), Type::Never(_)),
61    }
62}
63
64fn x86_64_asm_tokens(
65    inputs: &Punctuated<BareFnArg, Comma>,
66    never_return: bool,
67) -> proc_macro2::TokenStream {
68    let map_fnargs_to_reg_tokens = inputs.iter().enumerate().map(|(i, e)| {
69        let register_ident = X64_ARG_REGS[i];
70        if let Some(variable_str) = &e.name {
71            let variable_ident = variable_str.0.clone();
72            quote!(in(#register_ident) #variable_ident)
73        } else {
74            panic!("BareFnArg must have a name")
75        }
76    });
77
78    let input = if never_return {
79        quote! {
80            in("rax") rax,
81        }
82    } else {
83        quote! {
84            inout("rax") rax,
85        }
86    };
87
88    let mut options = quote! { options(nostack), };
89    if never_return {
90        options.append_all(quote! { options(noreturn), });
91    }
92
93    quote! {
94        core::arch::asm!(
95            "syscall",
96            #input
97            #(#map_fnargs_to_reg_tokens),*,
98            clobber_abi("system"),
99            #options
100        );
101    }
102}
proc_syscall/lib.rs

proc_syscall/
lib.rs
