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statics are null on x86_64-unknown-linux-none #134763

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m-mueller678 opened this issue Dec 25, 2024 · 2 comments · May be fixed by #134765
Open

statics are null on x86_64-unknown-linux-none #134763

m-mueller678 opened this issue Dec 25, 2024 · 2 comments · May be fixed by #134765
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C-bug Category: This is a bug. O-linux-none Operating system: Linux, with the libcless linux-none target T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.

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@m-mueller678
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m-mueller678 commented Dec 25, 2024 •
edited by Noratrieb
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when compiling for x86_64-unknown-linux-none, the static items in the following code snippet have null pointers as address. The inline versions work as expected. The exit code of the program is 10.

#![no_std]
#![no_main]

use syscalls::Sysno;

static SLICE: &[u8; 5] = b"hello";
static STRING:&str = "hello";

#[no_mangle]
pub extern "C" fn _start() -> ! {
    let static_slice = SLICE.as_ptr().is_null()  as usize;
    let inline_slice = b"hello".as_ptr().is_null() as usize;
    let static_str = STRING.as_ptr().is_null() as usize;
    let inline_str = "hello".as_ptr().is_null() as usize;
    let exit_code = static_slice<<3|inline_slice<<2|static_str<<1|inline_str;
    unsafe {
        syscalls::syscall1(Sysno::exit,exit_code).unwrap();
    }
    loop{}
}


#[panic_handler]
fn panic(_info: &core::panic::PanicInfo) -> ! {
    loop{}
}

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rustc --version --verbose:

rustc 1.85.0-nightly (409998c4e 2024-12-24)
binary: rustc
commit-hash: 409998c4e8cae45344fd434b358b697cc93870d0
commit-date: 2024-12-24
host: x86_64-unknown-linux-gnu
release: 1.85.0-nightly
LLVM version: 19.1.6

cargo config:

[build]
target = "x86_64-unknown-linux-none"

[unstable]
build-std = ["core"]
@m-mueller678 m-mueller678 added the C-bug Category: This is a bug. label Dec 25, 2024
@rustbot rustbot added the needs-triage This issue may need triage. Remove it if it has been sufficiently triaged. label Dec 25, 2024
@Noratrieb
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Noratrieb commented Dec 25, 2024 •
edited
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Your code sample does not compile, it has a syntax error and depends on a crate that you didn't specify in the cargo.toml. After adding the semicolon and removing the syscall (and also specifying panic=abort explicitly because this is incorrectly a panic=unwind target, fixed in #134765) I got a program.
The ELF is of type DYN, making it a position-independent executable. There are two relocations, probably for the statics.
With the default configuration, you're gonna have to implement a dynamic loader yourself to resolve these relocations. You can use the -Crelocation-model=static rustc flag to change this.
With that, the relocations are gone, it's no longer a PIE, and you should be able to run it without implementing a dynamic loader.
Maybe that should be the default for the target.

@Noratrieb Noratrieb added O-linux-none Operating system: Linux, with the libcless linux-none target T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. and removed needs-triage This issue may need triage. Remove it if it has been sufficiently triaged. labels Dec 25, 2024
@Noratrieb Noratrieb linked a pull request Dec 25, 2024 that will close this issue
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@Noratrieb
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Opened #134765 to change the defaults to more appropriate ones that should make your program work.

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Improve default target options for x86_64-unknown-linux-none Noratrieb/rust
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@m-mueller678 @rustbot @Noratrieb