std: make positioned I/O unsupported on VxWorks by JohnTitor · Pull Request #160031 · rust-lang/rust

JohnTitor · 2026-07-27T22:28:32Z

Currently, build-std for VxWorks fails because std calls pread/pwrite for positioned I/O.
Previously libc defined them as shims, but recently these were removed to align the actual state of SDK: rust-lang/libc#5129
It should make sense to return an unsupported error for VxWorks.
Fix rust-lang/libc#5328

rustbot · 2026-07-27T22:28:36Z

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Darksonn · 2026-07-28T08:55:19Z

Hmm, this is a bit messy. The current code has isolated all the conditional logic to this cfg_select!, but this PR introduces conditional logic in a bunch of other places.

If you do this, you can keep the conditional logic in one place:

Suggested change

cfg_select! {

target_os = "vxworks" => {

pub unsafe fn pread64(

_fd: c_int,

_buf: *mut c_void,

_count: size_t,

_offset: off64_t

) -> ssize_t {

-1

}

}

any(

all(target_os = "linux", not(target_env = "musl")),

target_os = "android",

target_os = "hurd",

) => {

// Prefer explicit pread64 for 64-bit offset independently of libc

// #[cfg(gnu_file_offset_bits64)].

use libc::pread64;

}

View changes since the review

Though it'd re-add shims, not returning the unsupported error. This PR's aim is to correct the behavior around it.

Uhm, after re-thinking about it, aligning the behavior might be overkill here, including overriding errno. For now, added shims as you suggested.

Darksonn

Thanks

@bors r+

View changes since this review

rust-bors · 2026-07-30T11:48:42Z

📌 Commit 84af593 has been approved by Darksonn

It is now in the queue for this repository.

…upported, r=Darksonn std: make positioned I/O unsupported on VxWorks Currently, build-std for VxWorks fails because std calls pread/pwrite for positioned I/O. Previously libc defined them as shims, but recently these were removed to align the actual state of SDK: rust-lang/libc#5129 It should make sense to return an unsupported error for VxWorks. Fix rust-lang/libc#5328

…uwer Rollup of 7 pull requests Successful merges: - #138230 (Add `raw_borrows_via_references` lint) - #160031 (std: make positioned I/O unsupported on VxWorks) - #159955 (Stop using higher-order macros to declare arenas) - #160164 (Derive `GenericTypeVisitable` for `RegionConstraint`) - #160177 (A few more "predicate"-to-"clause" renamings) - #160192 (Fix ICE for parsing issue with a closing brace) - #160209 (bootstrap: Remove method `Subcommand::kind`)

…uwer Rollup of 25 pull requests Successful merges: - #160204 (Sync from portable simd 2026 07 30) - #138230 (Add `raw_borrows_via_references` lint) - #158057 (Don't escape U+FF9E and U+FF9F in `escape_debug_ext`) - #160015 (refactor(mir-transform): Merge `can_be_overridden`, `is_required` and `is_enabled` into one) - #160031 (std: make positioned I/O unsupported on VxWorks) - #160125 (Fix typing mode handling in transmute checks and rustc_dump_layout) - #160152 (Create on-demand CI job for testing EC2 instances) - #160232 (rustdoc: fix ICE when a grapheme cluster joins a Prepend-class character to `_` or `:`) - #159214 (std: improve the documentation of the random feature) - #159818 (Resolve vars before calling `unnormalized_obligations`) - #159955 (Stop using higher-order macros to declare arenas) - #159958 (Fix avoid cycle for self referential return type notation) - #160040 (Split function parsing out of `item.rs` to a new module.) - #160044 (Add regression tests for fixed dead-code issues) - #160144 (renovate: group lockfiles PRs) - #160149 (Fix Windows on Arm PAC default) - #160164 (Derive `GenericTypeVisitable` for `RegionConstraint`) - #160175 (Try to recover less from incorrectly parsed const arg) - #160177 (A few more "predicate"-to-"clause" renamings) - #160181 (Mark `Tuple` and `FnPtr` traits `#[fundamental]`) - #160192 (Fix ICE for parsing issue with a closing brace) - #160209 (bootstrap: Remove method `Subcommand::kind`) - #160221 (Remove `Copy` supertrait from `VaList`) - #160223 (interpret: rename validate_operand → validate_place) - #160234 (Always use short ty path for call with missing arguments suggestion)

Rollup merge of #160031 - JohnTitor:vxworks-pread-pwrite-unsupported, r=Darksonn std: make positioned I/O unsupported on VxWorks Currently, build-std for VxWorks fails because std calls pread/pwrite for positioned I/O. Previously libc defined them as shims, but recently these were removed to align the actual state of SDK: rust-lang/libc#5129 It should make sense to return an unsupported error for VxWorks. Fix rust-lang/libc#5328

…uwer Rollup of 25 pull requests Successful merges: - rust-lang/rust#160204 (Sync from portable simd 2026 07 30) - rust-lang/rust#138230 (Add `raw_borrows_via_references` lint) - rust-lang/rust#158057 (Don't escape U+FF9E and U+FF9F in `escape_debug_ext`) - rust-lang/rust#160015 (refactor(mir-transform): Merge `can_be_overridden`, `is_required` and `is_enabled` into one) - rust-lang/rust#160031 (std: make positioned I/O unsupported on VxWorks) - rust-lang/rust#160125 (Fix typing mode handling in transmute checks and rustc_dump_layout) - rust-lang/rust#160152 (Create on-demand CI job for testing EC2 instances) - rust-lang/rust#160232 (rustdoc: fix ICE when a grapheme cluster joins a Prepend-class character to `_` or `:`) - rust-lang/rust#159214 (std: improve the documentation of the random feature) - rust-lang/rust#159818 (Resolve vars before calling `unnormalized_obligations`) - rust-lang/rust#159955 (Stop using higher-order macros to declare arenas) - rust-lang/rust#159958 (Fix avoid cycle for self referential return type notation) - rust-lang/rust#160040 (Split function parsing out of `item.rs` to a new module.) - rust-lang/rust#160044 (Add regression tests for fixed dead-code issues) - rust-lang/rust#160144 (renovate: group lockfiles PRs) - rust-lang/rust#160149 (Fix Windows on Arm PAC default) - rust-lang/rust#160164 (Derive `GenericTypeVisitable` for `RegionConstraint`) - rust-lang/rust#160175 (Try to recover less from incorrectly parsed const arg) - rust-lang/rust#160177 (A few more "predicate"-to-"clause" renamings) - rust-lang/rust#160181 (Mark `Tuple` and `FnPtr` traits `#[fundamental]`) - rust-lang/rust#160192 (Fix ICE for parsing issue with a closing brace) - rust-lang/rust#160209 (bootstrap: Remove method `Subcommand::kind`) - rust-lang/rust#160221 (Remove `Copy` supertrait from `VaList`) - rust-lang/rust#160223 (interpret: rename validate_operand → validate_place) - rust-lang/rust#160234 (Always use short ty path for call with missing arguments suggestion)

rustbot assigned Darksonn Jul 27, 2026

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Jul 27, 2026

Darksonn reviewed Jul 28, 2026

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Darksonn added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jul 28, 2026

JohnTitor mentioned this pull request Jul 30, 2026

std: make positional read/write unsupported on VxWorks #160075

Closed

std: make positioned I/O unsupported on VxWorks

84af593

JohnTitor force-pushed the vxworks-pread-pwrite-unsupported branch from 14b74b1 to 84af593 Compare July 30, 2026 11:44

JohnTitor 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 Jul 30, 2026

Darksonn approved these changes Jul 30, 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 Jul 30, 2026

JonathanBrouwer mentioned this pull request Jul 30, 2026

Rollup of 7 pull requests #160213

Closed

JonathanBrouwer mentioned this pull request Jul 30, 2026

Rollup of 25 pull requests #160238

Merged

tgross35 mentioned this pull request Jul 31, 2026

libc 0.2.187 dropped pread/pwrite for vxworks, but std still imports them rust-lang/libc#5328

Closed

rust-bors Bot merged commit 8310a37 into rust-lang:main Jul 31, 2026
13 checks passed

rustbot added this to the 1.99.0 milestone Jul 31, 2026

JohnTitor deleted the vxworks-pread-pwrite-unsupported branch July 31, 2026 11:13

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std: make positioned I/O unsupported on VxWorks - #160031

std: make positioned I/O unsupported on VxWorks#160031
rust-bors[bot] merged 1 commit into
rust-lang:mainfrom
JohnTitor:vxworks-pread-pwrite-unsupported

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+cfg_select! {
+    target_os = "vxworks" => {
+        pub unsafe fn pread64(
+            _fd: c_int,
+            _buf: *mut c_void,
+            _count: size_t,
+            _offset: off64_t
+        ) -> ssize_t {
+            -1
+        }
+    }
+    any(
+        all(target_os = "linux", not(target_env = "musl")),
+        target_os = "android",
+        target_os = "hurd",
+    ) => {
+        // Prefer explicit pread64 for 64-bit offset independently of libc
+        // #[cfg(gnu_file_offset_bits64)].
+        use libc::pread64;
+    }

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