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Add std support for armv7a-vex-v5 #145973

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@Tropix126 Tropix126 commented Aug 28, 2025 •
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This PR adds standard library support for the VEX V5 Brain (armv7a-vex-v5 target). It is more-or-less an updated version of the library-side work done in #131530.

This was a joint effort between me, @lewisfm, @max-niederman, @Gavin-Niederman and several other members of the vexide project.

Background

VEXos is a fairly unconventional operating system, with user code running in a restricted enviornment with regards to I/O capabilities and whatnot. As such, several OS-dependent APIs are unsupported or have partial support (such as std::net, std::process, and most of std::thread). A more comprehensive list of what does or doesn't work is outlined in the updated target documentation. Despite these limitations, we believe that libstd support on this target still has value to users, especially given the popular use of this hardware for educational purposes. For some previous discussion on this matter, see this comment.

SDK Linkage

VEXos doesn't really ship with an official libc or POSIX-style platform API (and though it does port newlib, these are stubbed on top of the underlying SDK). Instead, VEX provides their own SDK for calling platform APIs. Their official SDK is kept proprietary (with public headers), though open-source implementations exist. Following the precedent of the armv6k-nintendo-3ds team's work in #95897, we've opted not to directly link libstd to any SDK with the expectation that users will provide their own - either through vex-sdk-build (which will download the official SDK from VEX), vex-sdk-jumptable (a compatible, open-source reimplementation), or potentially through linking the PROS kernel. The vex-sdk crate used in the VEXos PAL provides libc-style FFI bindings for any compatible system library, so any of these options should work fine. A functional demo project using vex-sdk-build can be found here.

Future Work

This PR implements virtually everything we are currently able to implement given the current capabilities of the platform. The exception to this is file directory enumeration, though the implementation of that is sufficiently gross enough to drive us away from supporting this officially.

Additionally, I have a working branch implementing the panic_unwind runtime for this target, which is something that would be nice to see in the future, though given the volume of compiler changes i've deemed it out-of-scope for this PR.

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rustbot commented Aug 28, 2025

r? @tgross35

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@rustbot rustbot added A-tidy Area: The tidy tool S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-bootstrap Relevant to the bootstrap subteam: Rust's build system (x.py and src/bootstrap) T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Aug 28, 2025
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rustbot commented Aug 28, 2025

Some changes occurred in src/doc/rustc/src/platform-support

cc @Noratrieb

These commits modify the library/Cargo.lock file. Unintentional changes to library/Cargo.lock can be introduced when switching branches and rebasing PRs.

If this was unintentional then you should revert the changes before this PR is merged.
Otherwise, you can ignore this comment.

These commits modify compiler targets.
(See the Target Tier Policy.)

The list of allowed third-party dependencies may have been modified! You must ensure that any new dependencies have compatible licenses before merging.

cc @davidtwco, @wesleywiser

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I think the limitations here seem fine, and from a quick skim nothing jumps out to me as problematic. Nominating to make sure the team doesn't have any concerns.

@rustbot label +I-libs-nominated

@rustbot rustbot added the I-libs-nominated Nominated for discussion during a libs team meeting. label Aug 28, 2025
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@rustbot rustbot removed the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Aug 30, 2025
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rustbot commented Aug 30, 2025

Reminder, once the PR becomes ready for a review, use @rustbot ready.

@rustbot rustbot added the S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. label Aug 30, 2025
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@rustbot ready

@rustbot rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Aug 30, 2025
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Thanks for the updates here, I'll take a more thorough look through after the libs meeting (next Wednesday).

@tgross35 tgross35 added S-waiting-on-team Status: Awaiting decision from the relevant subteam (see the T-<team> label). and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Aug 30, 2025
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bors commented Sep 3, 2025

☔ The latest upstream changes (presumably #146160) made this pull request unmergeable. Please resolve the merge conflicts.

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rustbot commented Sep 5, 2025

Some changes occurred in src/tools/cargo

cc @ehuss

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rustbot commented Sep 5, 2025

This PR was rebased onto a different master commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

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Tropix126 commented Sep 5, 2025 •
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Submodule changes were unintentional, dealing with that :/

@Tropix126
vexos: move fs and stdio into respective modules
3317cd7
@Tropix126
vexos: implement global dlmalloc fallback
2fdd96d
@Tropix126
vexos: finish bringing modules up to date
a141abf
@Tropix126
vexos: provide dlmalloc::Allocator implementation
36d71f1
@Tropix126
vexos: block on stdout writes with size>2048
3989b2c
@Tropix126
format, tidy
0163635
@Tropix126
bump to vex-sdk 0.27.0
ba08497
@Tropix126
vexos: simplify logic by casting count to usize early
bed0127
@Tropix126
vexos: remove accidental semicolon
64a440f
@Tropix126
vexos: fix file opening logic
85025ad
@Tropix126
vexos: improve error message when opening files in RW mode
7e66bd1
@Tropix126
vexos: fix logic regarding create and create_new
4be4d68
@Tropix126
update armv7a-vex-v5 target documentation
21ef17d
@Tropix126
clarify details regarding system ABI, fix typos
6b85cc9
@Tropix126
simplify vexFileStatus check in fs::exists
70804e4
@Tropix126
remove unnecessary allocator lock on VEXos
c3a6373
@Tropix126
fmt
7eb898e
@Tropix126
switch to run_path_with_cstr for path conversion
7f8cb7d
@Tropix126
vexos: refactor FileAttr, clean up open logic
76b70ba
@Tropix126
vexos: improve unsafe hygiene in alloc and PAL, fix fs issues
4cc8721
@Tropix126
re-export relevant items from unsupported in vexos modules
9f67126
@Tropix126
fix type incompatibilities from unsupported re-exports
fb1b204
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bors commented Sep 6, 2025

☔ The latest upstream changes (presumably #146258) made this pull request unmergeable. Please resolve the merge conflicts.

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