Remove asm toolchain by wt · Pull Request #629 · rust-embedded/cortex-m

wt · 2026-03-11T04:13:41Z

This is a draft for updating the asm toolchain. It's based on my #628, so it shouldn't be landed before that is.

The `cm7-r0p1` feature only works with the plateform feature `armv7em`. I added a compile error to help someone figure that out more redily if they accidentally combine those features.

This will allow getting all the asm in shape for edition 2024.

wt · 2026-03-13T07:14:19Z

@thejpster Here's what you asked for.

Inline asm has been supported in stable rust for some time, so I removed the separate asm build infra and added that code to the normal crate code. I also crated a mock of the asm functions that were needed to run clippy with a non-arm target (like x86_64).

thejpster · 2026-03-13T07:18:05Z

.github/workflows/clippy.yml

+    strategy:
+      matrix:
+        # All generated code should be running on stable now
+        rust: [stable]


clippy should only be run on a fixed version, otherwise new releases that add new lints will break the build.

thejpster · 2026-03-13T07:18:55Z

.github/workflows/clippy.yml

+
+    # steps:
+    #   - uses: actions/checkout@v4
+    #   - uses: dtolnay/rust-toolchain@1.85


Can the commented out text be removed?

thejpster · 2026-03-13T07:19:37Z

Had a quick look on my phone - looks ok, just a few notes. I want to inspect the symbol table later when I get to a laptop.

wt · 2026-03-13T07:27:23Z

I removed the change to the clippy runs since I added the mock so that it can be run without issue with clippy targeting x86.

wt · 2026-03-13T07:28:47Z

If you want me to add that change to the tests back in for clippy I can. It was not really related to this change, so I didn't want to add more complexity.

Sympatron · 2026-03-13T12:44:22Z

cortex-m/src/asm.rs

+#[cfg_attr(any(armv6m, armv7m, armv7em, armv8m), path = "asm/inner.rs")]
+#[cfg_attr(
+    all(not(armv6m), not(armv7m), not(armv7em), not(armv8m)),
+    path = "asm/inner_mock.rs"
+)]


If I understand this correctly this changes the behavior from declaring an extern "C" unsafe fn for the asm functions (which is what call_asm! does if inline-asm is not enabled) to silently replacing all functions with nops if the target is not one of these.
Before this PR, it would be a compile time error if one of these functions is used on an unsupported target (I think).
Is this the intended new behavior?

I'm fine with that. If you are on an incompatible target, the point is to do enough to make clippy/unit tests/whatever happy, not do anything useful.

thejpster · 2026-03-14T15:27:54Z

cortex-m/src/asm/inner.rs

+use core::sync::atomic::{Ordering, compiler_fence};
+
+#[inline(always)]
+pub unsafe fn __bkpt() {


These need marking with #[unsafe(no_mangle)] to ensure they have the same symbol as the old asm functions.

Perhaps like:

#[unsafe(link_section = ".text.__function_name_goes_here")] #[cfg(not(feature = "inline-asm", unsafe(no_mangle)))] #[inline(always)] pub unsafe fn __bkpt() { // inline asm goes here }

That way, anyone who has written code like the following example will still find their code works when not using inline-asm:

extern "C" { fn __wfi(); } unsafe { __wfi(); }

And anyone who is using inline-asm will find the following still works:

#[unsafe(no_mangle)] pub extern "C" fn __wfi() { // do stuff }

OK, nah, we talked about this on Matrix and the __foo functions are not part of the public API - that's what the __ prefix means. So it's OK for the functions to be renamed.

In fact you could remove the __ prefixes from all these functions (and the mock functions). It adds no value and suggests a backwards compatibility that isn't actually present.

diondokter

Great, love it!

diondokter · 2026-03-14T15:47:20Z

cortex-m/src/interrupt.rs

 #[inline]
 pub fn disable() {
-    call_asm!(__cpsid());
+    unsafe { crate::asm::inner::__cpsid() };


We should probably call the public api when we can

diondokter · 2026-03-14T15:47:26Z

cortex-m/src/interrupt.rs

 #[inline]
 pub unsafe fn enable() {
-    call_asm!(__cpsie());
+    unsafe { crate::asm::inner::__cpsie() };


wt force-pushed the update_asm_toolchain branch 4 times, most recently from 0fe3a7c to 2abb7dd Compare March 12, 2026 21:06

wt marked this pull request as ready for review March 12, 2026 21:06

wt force-pushed the update_asm_toolchain branch 4 times, most recently from ec6c7ef to 667de8f Compare March 12, 2026 23:46

wt marked this pull request as draft March 12, 2026 23:46

wt force-pushed the update_asm_toolchain branch 8 times, most recently from b9cb8b5 to 74e91d2 Compare March 13, 2026 02:01

wt added 4 commits March 12, 2026 20:03

Document compatibility of the cm7-r0p1 feature.

6742d9e

The `cm7-r0p1` feature only works with the plateform feature `armv7em`. I added a compile error to help someone figure that out more redily if they accidentally combine those features.

Bump to asm toolchain to 1.94.0.

872ad7e

This will allow getting all the asm in shape for edition 2024.

Bump asm to edition 2024.

2499d14

Remove blob build/check from xtask crate.

0d2a810

wt force-pushed the update_asm_toolchain branch 8 times, most recently from 9cad22a to 256dc0f Compare March 13, 2026 04:09

wt force-pushed the update_asm_toolchain branch 15 times, most recently from 3a0b6e9 to 0d75936 Compare March 13, 2026 07:11

wt changed the title ~~Update asm toolchain~~ Remove asm toolchain Mar 13, 2026

wt marked this pull request as ready for review March 13, 2026 07:14

wt added 2 commits March 13, 2026 00:16

Remove the precompiled functions wrapping assembly routines.

29ef316

wt force-pushed the update_asm_toolchain branch from 0d75936 to e7d07d2 Compare March 13, 2026 07:17

thejpster reviewed Mar 13, 2026

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wt force-pushed the update_asm_toolchain branch from e7d07d2 to 29ef316 Compare March 13, 2026 07:26

Sympatron reviewed Mar 13, 2026

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thejpster reviewed Mar 14, 2026

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diondokter reviewed Mar 14, 2026

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thejpster Mar 14, 2026 •

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