Emit thumb code on VEX V5 by lewisfm · Pull Request #158762 · rust-lang/rust

lewisfm · 2026-07-04T04:45:45Z

This PR switches the default codegen for the VEX V5 target to emit Thumb-2 instructions, allowing for smaller binary sizes (on the programs I tested this change on, I saw a ~20% size decrease on average). The target is renamed to have the thumb prefix instead of the arm prefix because of the updated instruction set.

Since VEXos starts all programs in Arm32 mode, the program entrypoint is explicitly compiled as ARM code and now transitions to Thumb mode when calling _start.

Users can still use the updated target in Arm32 mode by specifying -Ctarget-feature=-thumb-mode.

cc @tropicaaal @Gavin-Niederman

rustbot · 2026-07-04T04:45:48Z

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

cc @Noratrieb

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

rustbot · 2026-07-04T04:45:50Z

r? @Kivooeo

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rust-log-analyzer · 2026-07-04T05:05:41Z

A job failed! Check out the build log: (web) (plain enhanced) (plain)

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  PR_CI_JOB: 1
  IMAGE: x86_64-gnu-llvm-21
##[endgroup]
    Updating crates.io index
error: failed to get `fnv` as a dependency of package `http v1.2.0`
    ... which satisfies dependency `http = "^1.1.0"` of package `ureq-proto v0.3.3`
    ... which satisfies dependency `ureq-proto = "^0.3.3"` of package `ureq v3.0.8`
    ... which satisfies dependency `ureq = "^3"` of package `citool v0.1.0 (/home/runner/work/rust/rust/src/ci/citool)`

Caused by:
  failed to load source for dependency `fnv`

Caused by:
  unable to update registry `crates-io`

Caused by:
  download of 3/f/fnv failed

Caused by:
  curl failed

Caused by:

Gavin-Niederman

LGTM

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tropicaaal · 2026-07-11T15:29:36Z


 **Tier: 3**

 Allows compiling user programs for the [VEX V5 Brain](https://www.vexrobotics.com/276-4810.html), a microcontroller for educational and competitive robotics.

 Rust support for this target is not affiliated with VEX Robotics or IFI, and does not link against any official VEX SDK.

+This target was previously named `armv7a-vex-v5`.


Not a blocker, but it might be a good idea for this to be elaborated on wrt. why we changed to thumb.

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tropicaaal

LGTM

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Kivooeo · 2026-08-05T02:44:11Z

@rustbot reroll (don't know anything about this targets and don't have bandwidth to figure it out)

rustbot · 2026-08-05T09:58:17Z

⚠️ Warning ⚠️

This PR is based on an upstream commit that is older than 28 days.

It's recommended to update your branch according to the rustc-dev-guide.

jieyouxu

Thanks. Given that this is a Tier 3 target and target maintainers are on board I'm happy to stamp this.

@bors r+ rollup

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rust-bors · 2026-08-05T09:59:15Z

📌 Commit 383d557 has been approved by jieyouxu

It is now in the queue for this repository.

@tropicaaal

Emit thumb code on VEX V5 This PR switches the default codegen for the VEX V5 target to emit Thumb-2 instructions, allowing for smaller binary sizes (on the programs I tested this change on, I saw a ~20% size decrease on average). The target is renamed to have the `thumb` prefix instead of the `arm` prefix because of the updated instruction set. Since VEXos starts all programs in Arm32 mode, the program entrypoint is explicitly compiled as ARM code and now transitions to Thumb mode when calling `_start`. Users can still use the updated target in Arm32 mode by specifying `-Ctarget-feature=-thumb-mode`. cc @tropicaaal @Gavin-Niederman

…uwer Rollup of 25 pull requests Successful merges: - #154585 (treat no_mangle_generic_items as hard error instead of lint warning) - #158147 (std: fix stack buffer overflow in Windows junction_point) - #160130 (Select cache values to verify by key fingerprint, not value fingerprint) - #160343 (Rename `OutlivesPredicate` to `OutlivesClause`) - #160360 (Remove rustc_middle dependency on rustc_hir_pretty) - #160387 (rustc_codegen_ssa: Correctly apply the static `--jobs-backend` limit to backend parallelism) - #160422 (move mir-opt miri tests to CI logic) - #160444 (Avoid resolving path keywords outside `TypeNS`) - #160510 (Resolver: (un)tracked borrows for `CmRefCell` made safe my unsafe speculative flag) - #155424 ([blocked] Link to proposed LLM policy in CONTRIBUTING and pull request template) - #158726 (std: move futex implementations into sys::sync::futex) - #158762 (Emit thumb code on VEX V5) - #159225 (Split IncrCompSession out of Session) - #159820 (Make the `rustc_unsafe_specialization_marker` attribute actually `unsafe`) - #160198 (Rework `smallest_range_containing` to handle duplicates) - #160362 (Split `SpannedTypeVisitor` into its own crate, `rustc_ty_walk`) - #160390 (autodiff: Handle slice-tailed DSTs in type trees) - #160420 (Suggest `cast_signed()` for overflowing signed integer literals) - #160516 (Add regression test for HRTB projection in closure) - #160520 (Add some tests for specialization) - #160522 (fix(bootstrap): Normalize the names of proc macro dependency crates) - #160523 (Add regression test for opaque type) - #160531 (docs: fix typo in AllowExprMetavar comment) - #160538 (Update expect messages in tcp.rs doc examples to follow the style guide) - #160548 (bootstrap: Register `coverage-map` and `coverage-run` aliases via a separate step)

@tropicaaal

Emit thumb code on VEX V5 This PR switches the default codegen for the VEX V5 target to emit Thumb-2 instructions, allowing for smaller binary sizes (on the programs I tested this change on, I saw a ~20% size decrease on average). The target is renamed to have the `thumb` prefix instead of the `arm` prefix because of the updated instruction set. Since VEXos starts all programs in Arm32 mode, the program entrypoint is explicitly compiled as ARM code and now transitions to Thumb mode when calling `_start`. Users can still use the updated target in Arm32 mode by specifying `-Ctarget-feature=-thumb-mode`. cc @tropicaaal @Gavin-Niederman

…uwer Rollup of 25 pull requests Successful merges: - #158147 (std: fix stack buffer overflow in Windows junction_point) - #160130 (Select cache values to verify by key fingerprint, not value fingerprint) - #160343 (Rename `OutlivesPredicate` to `OutlivesClause`) - #160360 (Remove rustc_middle dependency on rustc_hir_pretty) - #160387 (rustc_codegen_ssa: Correctly apply the static `--jobs-backend` limit to backend parallelism) - #160422 (move mir-opt miri tests to CI logic) - #160444 (Avoid resolving path keywords outside `TypeNS`) - #160510 (Resolver: (un)tracked borrows for `CmRefCell` made safe by unsafe speculative flag) - #155424 ([blocked] Link to proposed LLM policy in CONTRIBUTING and pull request template) - #158726 (std: move futex implementations into sys::sync::futex) - #158762 (Emit thumb code on VEX V5) - #159225 (Split IncrCompSession out of Session) - #159820 (Make the `rustc_unsafe_specialization_marker` attribute actually `unsafe`) - #160198 (Rework `smallest_range_containing` to handle duplicates) - #160362 (Split `SpannedTypeVisitor` into its own crate, `rustc_ty_walk`) - #160390 (autodiff: Handle slice-tailed DSTs in type trees) - #160420 (Suggest `cast_signed()` for overflowing signed integer literals) - #160501 (Add bootstrap CLI snapshot test for testing miri) - #160516 (Add regression test for HRTB projection in closure) - #160520 (Add some tests for specialization) - #160522 (fix(bootstrap): Normalize the names of proc macro dependency crates) - #160523 (Add regression test for opaque type) - #160531 (docs: fix typo in AllowExprMetavar comment) - #160538 (Update expect messages in tcp.rs doc examples to follow the style guide) - #160548 (bootstrap: Register `coverage-map` and `coverage-run` aliases via a separate step)

Emit thumb code on VEX V5

fbb6a44

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. 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 Jul 4, 2026

rustbot assigned Kivooeo Jul 4, 2026

Fix up suggested VEXos linker flags for thumb

383d557

Gavin-Niederman approved these changes Jul 4, 2026

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tropicaaal reviewed Jul 11, 2026

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tropicaaal approved these changes Jul 11, 2026

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rustbot assigned jieyouxu and unassigned Kivooeo Aug 5, 2026

jieyouxu closed this Aug 5, 2026

rustbot removed the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Aug 5, 2026

jieyouxu reopened this Aug 5, 2026

rustbot added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Aug 5, 2026

jieyouxu approved these changes Aug 5, 2026

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rust-bors Bot added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Aug 5, 2026

JonathanBrouwer mentioned this pull request Aug 5, 2026

Rollup of 25 pull requests #160557

Closed

JonathanBrouwer mentioned this pull request Aug 5, 2026

Rollup of 25 pull requests #160559

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Emit thumb code on VEX V5 - #158762

Emit thumb code on VEX V5#158762
lewisfm wants to merge 2 commits into
rust-lang:mainfrom
vexide:feat/vex-v5-thumb2

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