`windows-sys` without CRT?

[Zymlex]

As I see, windows-sys uses no_std, but still try to link with CRT.
Is it possible to use windows-sys without CRT?

upd: #1989 (comment)

[tim-weis]

Could you provide a repro?

I'm not sure I'm seeing the same as you are, however, the (failed) imports I see aren't actually from the CRT, but rather the SEH infrastructure (__CxxFrameHandler3, _CxxThrowException). I don't know where those are getting pulled in (or the memsets further down).

This is the repro I'm using:

Cargo.toml

[package]
name = "nostd_windows-sys"
version = "0.0.0"
edition = "2021"

[dependencies.windows-sys]
version = "0.36.1"
features = [
    "Win32_Foundation",
    "Win32_System_Threading",
]

src/main.rs

#![no_std]
#![no_main]

use core::panic::PanicInfo;

use windows_sys::Win32::System::Threading::{GetCurrentProcess, TerminateProcess};

#[panic_handler]
fn panic_abort(_info: &PanicInfo) -> ! {
    unsafe {
        let h = GetCurrentProcess();
        TerminateProcess(h, 1);
    };
    unreachable!();
}

#[no_mangle]
pub extern "C" fn EntryPoint() -> u32 {
    0
}

.cargo/config.toml

[build]
rustflags = [
    "-C", "link-arg=/ENTRY:EntryPoint"
]

(Note: I don't know why the linker cannot find the entry point.)

[riverar]

I'm seeing similar CRT functions getting referenced (__CxxFrameHandler3) as @Zymlex reported using @tim-weis's sample (after adding an empty eh_personality function and setting the subsystem):

...
 libcore-798bc7c2d986ac97.rlib(core-798bc7c2d986ac97.core.db87af78-cgu.0.rcgu.o) : error LNK2019: unresolved external symbol memcpy referenced in function _ZN4core3num7flt2dec8strategy6dragon15format_shortest17h09419dd069410d1fE
 libcore-798bc7c2d986ac97.rlib(core-798bc7c2d986ac97.core.db87af78-cgu.0.rcgu.o) : error LNK2019: unresolved external symbol memcmp referenced in function _ZN63_$LT$core..ffi..c_str..CStr$u20$as$u20$core..cmp..PartialEq$GT$2eq17h66848a7c3b9113a9E
 libcore-798bc7c2d986ac97.rlib(core-798bc7c2d986ac97.core.db87af78-cgu.0.rcgu.o) : error LNK2001: unresolved external symbol __CxxFrameHandler3
 libcore-798bc7c2d986ac97.rlib(core-798bc7c2d986ac97.core.db87af78-cgu.0.rcgu.o) : error LNK2001: unresolved external symbol _fltused

[ChrisDenton]

Using panic=abort would be an option for removing panic handling. Although it may also need lto=true to remove all panic handling infrastructure.

Also compiler-builtins can provide mem* functions.

But I don't think any of this has anything to do with windows-sys.

[riverar]

Using panic=abort would be an option for removing panic handling. Although it may also need lto=true to remove all panic handling infrastructure.

Also compiler-builtins can provide mem* functions.

Doesn't work for me.

[ChrisDenton]

Hm, this seems to have regressed in 1.60. For 1.59 and earlier the panic handling code is removed with panic=abort and lto.

[kennykerr]

The windows-sys crate only contains type and function declarations. There's no code, so I don't think this issue is specific to this crate.

[tim-weis]

@ChrisDenton I used to have

[profile.release]
panic = 'abort'
lto = 'fat'

in Cargo.toml, but that didn't change anything. This is using 1.63, so this at least doesn't contradict your hypothesis. Still, as Kenny points out, I cannot think of any way that the windows-sys crate could even pull in any CRT dependencies.

Seems to be an issue with my repro, or @Zymlex's, or rustc.

[kennykerr]

Rafael pointed out that the windows-sys crate does provide Clone implemenetations that look like this:

impl ::core::clone::Clone for IO_COUNTERS {
    fn clone(&self) -> Self {
        *self
    }
}

This can result in the Rust compiler, or LLVM, injecting calls to functions or intrinsics like memcpy. So while the windows-sys crate does not have any explicit dependency on the CRT, it is likely that you cannot get away from it in practice if Rust itself has such a dependency.

[kennykerr]

Does this help? #1992

[Zymlex]

Minimal sample: https://github.com/Zymlex/TestCRTLinking

msvcrt.lib passed explicitly in linker:

Link args

"C:\\Program Files (x86)\\Microsoft Visual Studio\\2022\\BuildTools\\VC\\Tools\\MSVC\\14.33.31629\\bin\\HostX64\\x64\\link.exe" "/NOLOGO" "C:\\Temp\\rustcFQAfsD\\symbols.o" "D:\\TestCRT\\target\\debug\\build\\windows_x86_64_msvc-0573644fe28a5604\\build_script_build-0573644fe28a5604.build_script_build.d23cf486-cgu.0.rcgu.o" "D:\\TestCRT\\target\\debug\\build\\windows_x86_64_msvc-0573644fe28a5604\\build_script_build-0573644fe28a5604.build_script_build.d23cf486-cgu.1.rcgu.o" "D:\\TestCRT\\target\\debug\\build\\windows_x86_64_msvc-0573644fe28a5604\\build_script_build-0573644fe28a5604.build_script_build.d23cf486-cgu.10.rcgu.o" "D:\\TestCRT\\target\\debug\\build\\windows_x86_64_msvc-0573644fe28a5604\\build_script_build-0573644fe28a5604.build_script_build.d23cf486-cgu.11.rcgu.o" "D:\\TestCRT\\target\\debug\\build\\windows_x86_64_msvc-0573644fe28a5604\\build_script_build-0573644fe28a5604.build_script_build.d23cf486-cgu.12.rcgu.o" "D:\\TestCRT\\target\\debug\\build\\windows_x86_64_msvc-0573644fe28a5604\\build_script_build-0573644fe28a5604.build_script_build.d23cf486-cgu.13.rcgu.o" "D:\\TestCRT\\target\\debug\\build\\windows_x86_64_msvc-0573644fe28a5604\\build_script_build-0573644fe28a5604.build_script_build.d23cf486-cgu.14.rcgu.o" "D:\\TestCRT\\target\\debug\\build\\windows_x86_64_msvc-0573644fe28a5604\\build_script_build-0573644fe28a5604.build_script_build.d23cf486-cgu.15.rcgu.o" "D:\\TestCRT\\target\\debug\\build\\windows_x86_64_msvc-0573644fe28a5604\\build_script_build-0573644fe28a5604.build_script_build.d23cf486-cgu.2.rcgu.o" "D:\\TestCRT\\target\\debug\\build\\windows_x86_64_msvc-0573644fe28a5604\\build_script_build-0573644fe28a5604.build_script_build.d23cf486-cgu.3.rcgu.o" "D:\\TestCRT\\target\\debug\\build\\windows_x86_64_msvc-0573644fe28a5604\\build_script_build-0573644fe28a5604.build_script_build.d23cf486-cgu.4.rcgu.o" "D:\\TestCRT\\target\\debug\\build\\windows_x86_64_msvc-0573644fe28a5604\\build_script_build-0573644fe28a5604.build_script_build.d23cf486-cgu.5.rcgu.o" "D:\\TestCRT\\target\\debug\\build\\windows_x86_64_msvc-0573644fe28a5604\\build_script_build-0573644fe28a5604.build_script_build.d23cf486-cgu.6.rcgu.o" "D:\\TestCRT\\target\\debug\\build\\windows_x86_64_msvc-0573644fe28a5604\\build_script_build-0573644fe28a5604.build_script_build.d23cf486-cgu.7.rcgu.o" "D:\\TestCRT\\target\\debug\\build\\windows_x86_64_msvc-0573644fe28a5604\\build_script_build-0573644fe28a5604.build_script_build.d23cf486-cgu.8.rcgu.o" "D:\\TestCRT\\target\\debug\\build\\windows_x86_64_msvc-0573644fe28a5604\\build_script_build-0573644fe28a5604.build_script_build.d23cf486-cgu.9.rcgu.o" "D:\\TestCRT\\target\\debug\\build\\windows_x86_64_msvc-0573644fe28a5604\\build_script_build-0573644fe28a5604.526mukq0e2230mny.rcgu.o" "/LIBPATH:D:\\TestCRT\\target\\debug\\deps" "/LIBPATH:D:\\Rust\\rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib" "D:\\Rust\\rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib\\libstd-8423b2aaecc07cbd.rlib" "D:\\Rust\\rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib\\libpanic_unwind-140625d412b34ac2.rlib" "D:\\Rust\\rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib\\librustc_demangle-6b3a560234908e6a.rlib" "D:\\Rust\\rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib\\libstd_detect-e813d6686824bdf5.rlib" "D:\\Rust\\rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib\\libhashbrown-f70691b8a0682d5c.rlib" "D:\\Rust\\rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib\\libminiz_oxide-c56fd5f6dd80139a.rlib" "D:\\Rust\\rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib\\libadler-07da6c35c286f881.rlib" "D:\\Rust\\rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib\\librustc_std_workspace_alloc-3609338aefc74bee.rlib" "D:\\Rust\\rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib\\libunwind-75617f1352752ad2.rlib" "D:\\Rust\\rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib\\libcfg_if-d095611f20a3926f.rlib" "D:\\Rust\\rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib\\liblibc-863480ba106f69c6.rlib" "D:\\Rust\\rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib\\liballoc-b88f15a049f875f2.rlib" "D:\\Rust\\rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib\\librustc_std_workspace_core-69892fa511d5a698.rlib" "D:\\Rust\\rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib\\libcore-798bc7c2d986ac97.rlib" "D:\\Rust\\rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib\\libcompiler_builtins-7738daf2e99ec4b2.rlib" "advapi32.lib" "userenv.lib" "kernel32.lib" "ws2_32.lib" "bcrypt.lib" "msvcrt.lib" "legacy_stdio_definitions.lib" "/NXCOMPAT" "/LIBPATH:D:\\Rust\\rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\lib" "/OUT:D:\\TestCRT\\target\\debug\\build\\windows_x86_64_msvc-0573644fe28a5604\\build_script_build-0573644fe28a5604.exe" "/OPT:REF,NOICF" "/DEBUG" "/NATVIS:D:\\Rust\\rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\etc\\intrinsic.natvis" "/NATVIS:D:\\Rust\\rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\etc\\liballoc.natvis" "/NATVIS:D:\\Rust\\rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\etc\\libcore.natvis" "/NATVIS:D:\\Rust\\rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\etc\\libstd.natvis" "/NODEFAULTLIB" "/SUBSYSTEM:WINDOWS" "/ENTRY:main_entry_point" "/VERBOSE" "/WX"

[Zymlex]

This set is also of interest:

"advapi32.lib" "userenv.lib" "kernel32.lib" "ws2_32.lib" "bcrypt.lib" "msvcrt.lib" "legacy_stdio_definitions.lib"

[riverar]

So, no_std is a toggle between std and core crates and relies on toolchains, crates, etc. all working together to realize the "no standard library" vision, which seems to be somewhat nebulously defined in my reading. It does not appear there is any work to be done on the windows-sys side, so I'm going to close this issue.

That said, I recognize that without a real working end-to-end example, this all feels like a sham. You might want to get the ball rolling on https://github.com/rust-lang/rust/issues.

Some issues to keep an eye on:

• __CxxFrameHandler3 still referenced even though panic=abort rust-lang/rust#101134
• rustc always links against non-debug Windows runtime rust-lang/rust#39016
• (any others?)

[Zymlex]

Managed to figure it out! Due to a bug, it is necessary to pass arguments through environment variables + cargo args:

RUSTFLAGS=-Clink-arg=/NODEFAULTLIB -Clink-arg=/SUBSYSTEM:WINDOWS -Clink-arg=/ENTRY:main_entry_point -Clink-arg=/VERBOSE -Clink-arg=/WX

cargo build --package test_crt -Zbuild-std=core --target x86_64-pc-windows-msvc --verbose

So I was able to build without CRT, Winsock and other...