Rollup of 2 pull requests by JonathanBrouwer · Pull Request #156574 · rust-lang/rust

JonathanBrouwer · 2026-05-14T13:53:10Z

Successful merges:

Add lint againts invalid runtime symbol definitions #155521 (Add lint againts invalid runtime symbol definitions)
Disable main_needs_argc_argv for Wasm #156571 (Disable main_needs_argc_argv for Wasm)

Add lint againts invalid runtime symbol definitions This PR adds a deny-by-default lint againts invalid runtime symbol definitions, those runtime symbols are assumed and used by `core`[^1] and `rustc` with a specific definition. We have had multiple reports of users tripping over `std` symbols (addressed in a future PR): - [Why does `#[no_mangle] fn open() {}` make `cargo t` hang?](https://users.rust-lang.org/t/why-does-no-mangle-fn-open-make-cargo-t-hang/103423) - [Pointer becomes misaligned in test with `no_mangle`](https://users.rust-lang.org/t/pointer-becomes-misaligned-in-test-with-no-mangle/126580) This PR is a second attempt after rust-lang#146505, where T-lang had [some reservations](rust-lang#146505 (comment)) about a blanket lint that does not check the signature, which is now done with this PR, and about linting of `std` runtime symbols when std is not linked, which this PR omits by not including any std runtime symbols (for now). ## `invalid_runtime_symbol_definitions` *(deny-by-default)* The `invalid_runtime_symbol_definitions` lint checks the signature of items whose symbol name is a runtime symbols expected by `core`. ### Example ```rust,compile_fail #[unsafe(no_mangle)] pub fn memcmp() {} // invalid definition of the `memcmp` runtime symbol ``` ```text error: invalid definition of the runtime `memcmp` symbol used by the standard library --> a.rs:2:1 | 4 | fn memcmp() {} | ^^^^^^^^^^^ | = note: expected `unsafe extern "C" fn(*const c_void, *const c_void, usize) -> i32` found `fn()` = help: either fix the signature or remove any attributes like `#[unsafe(no_mangle)]`, `#[unsafe(export_name = "memcmp")]`, or `#[link_name = "memcmp"]` = note: `#[deny(invalid_runtime_symbol_definitions)]` on by default ``` ### Explanation Up-most care is required when defining runtime symbols assumed and used by the standard library. They must follow the C specification, not use any standard-library facility or undefined behavior may occur. The symbols currently checked are `memcpy`, `memmove`, `memset`, `memcmp`, `bcmp` and `strlen`. [^1]: https://doc.rust-lang.org/core/index.html#how-to-use-the-core-library

@hoodmane

Disable `main_needs_argc_argv` for Wasm AFAIU this explains to the "Rust Runtime" that `main()` doesn't need `argc`/`argv`. Newer Wasm targets have explicitly disabled this, this PR changes it so that the base Wasm configuration affecting all Wasm targets disables this now. This affects the following targets: - `wasm32-unknown-unknown` - `wasm32v1-none` - `wasm64-unknown-unknown` The only Wasm target where `main_needs_argc_argv` is still enabled is `wasm32-unknown-emscripten`. @hoodmane let me know and I can remove it there as well. Credit goes to @Spxg for stumbling on this. r? @alexcrichton

JonathanBrouwer · 2026-05-14T13:53:39Z

@bors r+ rollup=never p=5

rust-bors · 2026-05-14T13:53:43Z

📌 Commit b128690 has been approved by JonathanBrouwer

It is now in the queue for this repository.

…uwer Rollup of 2 pull requests Successful merges: - #155521 (Add lint againts invalid runtime symbol definitions) - #156571 (Disable `main_needs_argc_argv` for Wasm)

rust-log-analyzer · 2026-05-14T14:35:45Z

The job dist-various-2 failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

    |
 52 | / macro_rules! intrinsics {
 53 | |     () => ();
...   |
415 | |             unsafe extern $abi fn $name( $($argname: $ty),* ) $(-> $ret)? {
    | |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
...   |
485 | |     );
486 | | }
    | |_- in this expansion of `intrinsics!`
    |
   ::: /rustc/77f0eecdc7f0b33434e3c3e20a3bd88865a780bd/library/compiler-builtins/compiler-builtins/src/mem/mod.rs:10:1
    |
 10 | / intrinsics! {
 11 | |     #[mem_builtin]
 12 | |     pub unsafe extern "C" fn memcpy(dest: *mut u8, src: *const u8, n: usize) -> *mut u8 {
 13 | |         impls::copy_forward(dest, src, n);
...   |
 50 | | }
    | |_- in this macro invocation
    |
    = note: expected `unsafe extern "C" fn(*mut c_void, *const c_void, usize) -> *mut c_void`
            found    `unsafe extern "C" fn(*mut u8, *const u8, usize) -> *mut u8`
    = help: either fix the signature or remove any attributes like `#[unsafe(no_mangle)]`, `#[unsafe(export_name = "memcpy")]`, or `#[link_name = "memcpy"]`
    = note: `#[deny(invalid_runtime_symbol_definitions)]` on by default

error: invalid definition of the runtime `memmove` symbol used by the standard library
   --> /rustc/77f0eecdc7f0b33434e3c3e20a3bd88865a780bd/library/compiler-builtins/compiler-builtins/src/macros.rs:415:13
    |
 52 | / macro_rules! intrinsics {
 53 | |     () => ();
...   |
415 | |             unsafe extern $abi fn $name( $($argname: $ty),* ) $(-> $ret)? {
    | |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
...   |
420 | |         intrinsics!($($rest)*);
    | |         ---------------------- in this macro invocation (#2)
...   |
485 | |     );
486 | | }
    | | -
    | | |
    | |_in this expansion of `intrinsics!` (#1)
    |   in this expansion of `intrinsics!` (#2)
    |
   ::: /rustc/77f0eecdc7f0b33434e3c3e20a3bd88865a780bd/library/compiler-builtins/compiler-builtins/src/mem/mod.rs:10:1
    |
 10 | / intrinsics! {
 11 | |     #[mem_builtin]
 12 | |     pub unsafe extern "C" fn memcpy(dest: *mut u8, src: *const u8, n: usize) -> *mut u8 {
 13 | |         impls::copy_forward(dest, src, n);
...   |
 50 | | }
    | |_- in this macro invocation (#1)
    |
    = note: expected `unsafe extern "C" fn(*mut c_void, *const c_void, usize) -> *mut c_void`
            found    `unsafe extern "C" fn(*mut u8, *const u8, usize) -> *mut u8`
    = help: either fix the signature or remove any attributes like `#[unsafe(no_mangle)]`, `#[unsafe(export_name = "memmove")]`, or `#[link_name = "memmove"]`

error: invalid definition of the runtime `memset` symbol used by the standard library
   --> /rustc/77f0eecdc7f0b33434e3c3e20a3bd88865a780bd/library/compiler-builtins/compiler-builtins/src/macros.rs:415:13
    |
 52 | / macro_rules! intrinsics {
 53 | |     () => ();
...   |
415 | |             unsafe extern $abi fn $name( $($argname: $ty),* ) $(-> $ret)? {
    | |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
...   |
420 | |         intrinsics!($($rest)*);
    | |         ----------------------
    | |         |
    | |         in this macro invocation (#2)
    | |         in this macro invocation (#3)
...   |
---
    |   in this expansion of `intrinsics!` (#3)
    |
   ::: /rustc/77f0eecdc7f0b33434e3c3e20a3bd88865a780bd/library/compiler-builtins/compiler-builtins/src/mem/mod.rs:10:1
    |
 10 | / intrinsics! {
 11 | |     #[mem_builtin]
 12 | |     pub unsafe extern "C" fn memcpy(dest: *mut u8, src: *const u8, n: usize) -> *mut u8 {
 13 | |         impls::copy_forward(dest, src, n);
...   |
 50 | | }
    | |_- in this macro invocation (#1)
    |
    = note: expected `unsafe extern "C" fn(*mut c_void, i32, usize) -> *mut c_void`
            found    `unsafe extern "C" fn(*mut u8, i32, usize) -> *mut u8`
    = help: either fix the signature or remove any attributes like `#[unsafe(no_mangle)]`, `#[unsafe(export_name = "memset")]`, or `#[link_name = "memset"]`

error: invalid definition of the runtime `memcmp` symbol used by the standard library
   --> /rustc/77f0eecdc7f0b33434e3c3e20a3bd88865a780bd/library/compiler-builtins/compiler-builtins/src/macros.rs:415:13
    |
 52 | / macro_rules! intrinsics {
 53 | |     () => ();
...   |
415 | |             unsafe extern $abi fn $name( $($argname: $ty),* ) $(-> $ret)? {
    | |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
...   |
420 | |         intrinsics!($($rest)*);
    | |         ----------------------
    | |         |
    | |         in this macro invocation (#2)
    | |         in this macro invocation (#3)
...   |
---
    |   in this expansion of `intrinsics!` (#3)
    |
   ::: /rustc/77f0eecdc7f0b33434e3c3e20a3bd88865a780bd/library/compiler-builtins/compiler-builtins/src/mem/mod.rs:10:1
    |
 10 | / intrinsics! {
 11 | |     #[mem_builtin]
 12 | |     pub unsafe extern "C" fn memcpy(dest: *mut u8, src: *const u8, n: usize) -> *mut u8 {
 13 | |         impls::copy_forward(dest, src, n);
...   |
 50 | | }
    | |_- in this macro invocation (#1)
    |
    = note: expected `unsafe extern "C" fn(*const c_void, *const c_void, usize) -> i32`
            found    `unsafe extern "C" fn(*const u8, *const u8, usize) -> i32`
    = help: either fix the signature or remove any attributes like `#[unsafe(no_mangle)]`, `#[unsafe(export_name = "memcmp")]`, or `#[link_name = "memcmp"]`

error: invalid definition of the runtime `bcmp` symbol used by the standard library
   --> /rustc/77f0eecdc7f0b33434e3c3e20a3bd88865a780bd/library/compiler-builtins/compiler-builtins/src/macros.rs:415:13
    |
 52 | / macro_rules! intrinsics {
 53 | |     () => ();
...   |
415 | |             unsafe extern $abi fn $name( $($argname: $ty),* ) $(-> $ret)? {
    | |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
...   |
420 | |         intrinsics!($($rest)*);
    | |         ----------------------
    | |         |
    | |         in this macro invocation (#2)
    | |         in this macro invocation (#3)
...   |
---
    |   in this expansion of `intrinsics!` (#3)
    |
   ::: /rustc/77f0eecdc7f0b33434e3c3e20a3bd88865a780bd/library/compiler-builtins/compiler-builtins/src/mem/mod.rs:10:1
    |
 10 | / intrinsics! {
 11 | |     #[mem_builtin]
 12 | |     pub unsafe extern "C" fn memcpy(dest: *mut u8, src: *const u8, n: usize) -> *mut u8 {
 13 | |         impls::copy_forward(dest, src, n);
...   |
 50 | | }
    | |_- in this macro invocation (#1)
    |
    = note: expected `unsafe extern "C" fn(*const c_void, *const c_void, usize) -> i32`
            found    `unsafe extern "C" fn(*const u8, *const u8, usize) -> i32`
    = help: either fix the signature or remove any attributes like `#[unsafe(no_mangle)]`, `#[unsafe(export_name = "bcmp")]`, or `#[link_name = "bcmp"]`

[RUSTC-TIMING] compiler_builtins test:false 1.369
error: could not compile `compiler_builtins` (lib) due to 5 previous errors
warning: build failed, waiting for other jobs to finish...
[RUSTC-TIMING] core test:false 16.806

rust-bors · 2026-05-14T14:37:03Z

💔 Test for 77f0eec failed: CI. Failed job:

auto - dist-various-2 (web logs, enhanced plaintext logs)

rust-bors · 2026-05-14T14:49:43Z

PR #156571, which is a member of this rollup, was unapproved.

rust-bors · 2026-05-14T15:03:53Z

PR #155521, which is a member of this rollup, was unapproved.

Urgau and others added 9 commits May 14, 2026 12:41

Add function to extract the symbol name from the attributes

0f280d4

Add weak-only lang items for core runtime symbols

8b67ab3

Add lint against invalid runtime symbol definitions

426706d

Handle static whose type is a function pointer

50306e1

Fix invalid memcpy definition in codegen test and UI tests

453192d

Fix invalid definition of strlen in error codes documentation

32aa35c

Disable main_needs_argc_argv for Wasm

072be06

rust-bors Bot added the rollup A PR which is a rollup label May 14, 2026

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 May 14, 2026

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rust-bors Bot mentioned this pull request May 14, 2026

Disable main_needs_argc_argv for Wasm #156571

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JonathanBrouwer mentioned this pull request May 14, 2026

Add lint againts invalid runtime symbol definitions #155521

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Rollup of 2 pull requests#156574

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