rustc always links against non-debug Windows runtime #39016

jdm · 2017-01-12T16:00:41Z

When building rust-mozjs with debug symbols enabled, the underlying C++ library links against the debug Windows runtime (msvcrtd.lib) rather than the regular one (msvcrt.lib). Unfortunately, rustc always links against msvcrt.lib unconditionally:

rust/src/vendor/libc/src/windows.rs

Line 150 in da2ce22

#[link(name = "msvcrt")]

. This makes it impossible to build a debug-enabled version of rust-mozjs on Windows.

The text was updated successfully, but these errors were encountered:

jdm · 2017-01-12T16:04:05Z

Would there be any objection to doing something like:

#[cfg(all(target_env = "msvc", debug))] // " if " -- appease style checker
#[link(name = "msvcrtd")]
extern {}

#[cfg(all(target_env = "msvc", not(debug_assertions)))] // " if " -- appease style checker
#[link(name = "msvcrt")]
extern {}

cc @retep998

retep998 · 2017-01-12T16:17:41Z

We already have a feature for choosing whether to link the static or dynamic CRT. It would be a fairly trivial matter to add another feature to choose whether to link the debug or release CRT (which I did suggest but nobody seemed to notice). I'd rather not tie this sort of thing to whether optimizations are enabled.

jdm · 2017-01-23T19:50:58Z

@retep998 says that the way to fix this is to find the relevant bits in #37545 and duplicate it for crt-debug.

nox · 2017-10-07T10:45:40Z

#37545 landed, what is needed to make some progress on this?

retep998 · 2017-10-07T11:13:14Z

@nox As I said before, someone has to find the relevant bits in #37545 and duplicate it for crt-debug.

asajeffrey · 2018-05-15T15:15:35Z

This cost me a couple of days debugging why debugmozjs builds of mozjs_sys were failing with link errors under msvc.

Neurrone · 2018-09-03T13:02:40Z

Would love to be able to configure this as well for c++ code.

jdm · 2019-07-09T15:54:41Z

It would make sense to transfer this issue to https://github.com/rust-lang/libc now that the responsible code is in that repository, but I don't have the permissions to do so.

gnzlbg · 2019-07-09T16:58:46Z

cc @alexcrichton @retep998 @newpavlov - please review the libc C PR at: rust-lang/libc#1433 - I'm not sure how this will interact with linking libc both via libstd and crates.io, what happens if the features are different in each, what happens if the binary is #[no_std] and no libstd is linked, etc.

retep998 · 2019-08-28T16:55:18Z

Solving this issue requires changes both in rust and libc.

gnzlbg · 2019-08-28T18:22:53Z

Since libstd depends on libc, and libc would need to be compiled differently for debug and release on windows, wouldn't we need to ship two libstds one for debug and one for release ?

retep998 · 2019-08-28T18:32:12Z

Only if there are actual changes to the bindings in libc depending on debug vs release. Simply linking to a different CRT is already handled in std's libc using deferred linking decisions.

upsuper · 2020-01-03T09:27:48Z

This looks like a pretty big footgun, and it can cause mysterious runtime error taking people lots of time to figure out. Until this gets fixed, there should probably be some document / compiler message warning about this, so that people know that they need to have their C/C++ program always link against the non-debug crt.

nox · 2020-02-20T10:08:16Z

I'm curious how this can be done cleanly, when the base windows target itself adds -lmsvcrt directly into the link args.

The glue is done using the [cxx crate](https://cxx.rs/) on the Rust side. As a proof-of-concept, only a small console command (`rust_version`) printing the currently used Rust version was added. You can generate and open the Rust documentation using `DDNET_TEST_NO_LINK=1 cargo doc --open`. You can run the Rust tests using `cmake --build <build dir> --target run_rust_tests`, they're automatically included in the `run_tests` target as well. Rust tests don't work on Windows in debug mode on Windows because Rust cannot currently link with the debug version of the C stdlib on Windows: rust-lang/rust#39016. --- The stuff in `src/rust-bridge` is generated using ``` cxxbridge src/engine/shared/rust_version.rs --output src/rust-bridge/engine/shared/rust_version.cpp --output src/rust-bridge/engine/shared/rust_version.h cxxbridge src/engine/console.rs --output src/rust-bridge/cpp/console.cpp --output src/rust-bridge/cpp/console.h ```

5599: Add support for Rust code in DDNet r=def- a=heinrich5991 The glue is done using the [cxx crate](https://cxx.rs/) on the Rust side. As a proof-of-concept, only a small console command (`rust_version`) printing the currently used Rust version was added. You can generate and open the Rust documentation using `DDNET_TEST_NO_LINK=1 cargo doc --open`. You can run the Rust tests using `cmake --build <build dir> --target run_rust_tests`, they're automatically included in the `run_tests` target as well. Rust tests don't work on Windows in debug mode on Windows because Rust cannot currently link with the debug version of the C stdlib on Windows: rust-lang/rust#39016. --- The stuff in `src/rust-bridge` is generated using ``` cxxbridge src/engine/shared/rust_version.rs --output src/rust-bridge/engine/shared/rust_version.cpp --output src/rust-bridge/engine/shared/rust_version.h cxxbridge src/engine/console.rs --output src/rust-bridge/cpp/console.cpp --output src/rust-bridge/cpp/console.h ``` Co-authored-by: heinrich5991 <heinrich5991@gmail.com>

ChrisDenton · 2023-03-30T19:30:10Z

I really want to find a way forward here as it's a common issue when trying to integrate Rust with existing C/C++ builds.

I do find it slightly odd that linking the C runtime is the responsibility of the libc crate on Windows. That seems unusual compared to other platforms? But ok, I can live with that.

@petrochenkov suggested adding a feature in people's Cargo.toml, which seems a bit odd for this? Like I'm not entirely clear how this will work in practice without special Cargo support, otherwise it puts a lot of the effort of supporting this onto crate authors. A global --cfg (i.e. set in rustflags) might work better. It is super important that everything agrees on which CRT to use. Though I'm still not clear on the benefits of --cfg over a compiler codegen option.

So to sum up I think to do this outside of rustc will require changes to:

libc needs additional #[link(name = "...", cfg(...))] options
cc needs to be able understand these target cfgs
rustc needs to document that the special cfg name(s) are reserved for this use

Is that right?

Btw, there should also be an option to not link a CRT. This is the default for no_std on Windows but is not yet supported for std builds. Having this option is important for more exotic CRTs.

danakj · 2023-04-19T16:51:18Z

Hitting this issue in Chromium: https://bugs.chromium.org/p/chromium/issues/detail?id=1434719

Rust by default links with the default MSVCRT, (dynamic, release). MSVCRT's cannot be mixed, so if Meson compiles a C or C++ library and links it with the debug MSVCRT, then tries to link that with the Rust library there will be failures. There is no built-in way to fix this for rustc, so as a workaround we inject the correct arguments early in the linker line (before any libs at least) to change the runtime. This seems to work and is recommended as workaround in the upstream rust bug report: rust-lang/rust#39016. Given that this bug report has been opened since 2017, it seems unlikely to be fixed anytime soon, and affects all (currently) released versions of Rust.

jdm added the O-windows-msvc Toolchain: MSVC, Operating system: Windows label Jan 12, 2017

jdm mentioned this issue Jan 12, 2017

Build with debugmozjs to run automated tests servo/servo#14766

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alexcrichton added the T-tools label Jan 13, 2017

This was referenced Jan 27, 2017

Enable incremental GC. servo/servo#7621

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Run automated tests using debugmozjs servo/servo#14759

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Mark-Simulacrum added T-dev-tools Relevant to the dev-tools subteam, which will review and decide on the PR/issue. and removed T-tools labels May 24, 2017

Mark-Simulacrum added C-bug Category: This is a bug. C-feature-request Category: A feature request, i.e: not implemented / a PR. and removed C-bug Category: This is a bug. labels Jul 26, 2017

jdm mentioned this issue Jul 1, 2019

debugmozjs build is not supported on Windows servo/mozjs#189

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This was referenced Jul 9, 2019

Add a crt-debug target feature #62534

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Link to Windows debug CRTs when crt-debug target_feature is present. rust-lang/libc#1433

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jdm self-assigned this Jul 9, 2019

piscisaureus mentioned this issue Aug 30, 2019

Use cargo_gn to build using "cargo build" denoland/deno#2836

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JaFenix mentioned this issue Sep 23, 2019

Even debug builds try to link MSVCRT MT_StaticRelease of SKIA RazrFalcon/resvg#179

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example app crash when clicked button on wxMSW debug build kenz-gelsoft/wxRust2#36

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riverar mentioned this issue Aug 29, 2022

windows-sys without CRT? microsoft/windows-rs#1989

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heinrich5991 mentioned this issue Oct 19, 2022

Add support for Rust code in DDNet ddnet/ddnet#5599

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This was referenced Mar 30, 2023

use debug version of C runtime with MSVC rust-lang/cc-rs#717

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[DRAFT] MSVC: Add msvc_crt_link options rust-lang/libc#3178

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Windows MSVC CRT linking rust-lang/libs-team#211

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Cannot override Windows runtime for rust tests #116900

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Librashader.lib not being compiled as static SnowflakePowered/librashader#20

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Linking error when building rust crate in debug mode on Windows kuzudb/kuzu#3225

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Link MSVC default lib in core #122268

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Possible to allow msvcrtd linking for static builds in debug mode? SnowflakePowered/librashader#110

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rustc always links against non-debug Windows runtime #39016

rustc always links against non-debug Windows runtime #39016

jdm commented Jan 12, 2017

jdm commented Jan 12, 2017 •

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retep998 commented Jan 12, 2017 •

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jdm commented Jan 23, 2017

nox commented Oct 7, 2017

retep998 commented Oct 7, 2017

asajeffrey commented May 15, 2018

Neurrone commented Sep 3, 2018

jdm commented Jul 9, 2019

gnzlbg commented Jul 9, 2019

retep998 commented Aug 28, 2019

gnzlbg commented Aug 28, 2019

retep998 commented Aug 28, 2019

upsuper commented Jan 3, 2020

nox commented Feb 20, 2020

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danakj commented Apr 19, 2023

rustc always links against non-debug Windows runtime #39016

rustc always links against non-debug Windows runtime #39016

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