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.

.github/workflows/clippy.yml

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.

cortex-m/src/asm.rs

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.

K. I'll remove those __'s.

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

This is the public API for turning interrupts on and off - cpsie and cpsid are not exposed as individual functions.

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 · 2026-03-16T07:55:36Z

Since we are considering double underscored functions to be internal only, can I also get rid of this? The links keys have long been an proper way to do what this is trying to do.

jonathanpallant · 2026-03-16T09:05:39Z

Since we are considering double underscored functions to be internal only, can I also get rid of this? The links keys have long been an proper way to do what this is trying to do.

Maybe? But I wouldn't do it in this PR.

adamgreig · 2026-03-17T02:49:09Z

Since we are considering double underscored functions to be internal only, can I also get rid of this? The links keys have long been an proper way to do what this is trying to do.

We should get rid of this eventually, but it has to be handled carefully because the whole point is to prevent linking multiple versions of cortex-m-rt, and old versions don't have the links key set in Cargo.toml. I think if we replaced it we'd be best doing it in a new 0.8/1.0 release with the final 0.7 release having links set, and then rely on the semver-hacked 0.5/0.6 releases meaning most old versions will pull in a version with 0.7 and thus with links.

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).

wt · 2026-03-18T07:07:48Z

@thejpster @jonathanpallant @adamgreig

Reviewers, please double check the new crate (in cortex-m/macros). I'm assuming that the cortex-m crate using the new crate will need to be updated to use an actual version once it is published. Can we just publish the new crate once this is landed so that I can make a PR to depend on the published version?

thejpster · 2026-03-18T09:04:28Z

You can depend on a version and a path at the same time.

wt · 2026-03-19T06:30:21Z

You can depend on a version and a path at the same time.

Can I depend on a path in a published crate, like "cortex-m"?

jonathanpallant · 2026-03-19T12:08:10Z

https://github.com/rust-embedded/aarch32/blob/a7d4d1ce255a5dc783edf5f990e279c979e131f3/aarch32-rt/Cargo.toml#L40

As long as you have both. It uses the path if valid, and falls back to the version if not.

The purpose of this attribute is to allow platforms that do not support the asm instructions to compile code code that calls those functions. This is needed so that clippy can be run once in CI and when testing locally.

wt · 2026-03-19T22:54:55Z

I have updated the dep spec for the new crate to include the version number. I use an exact version like the cortex-m-rt crate does for cortex-m-rt-macros.

jonathanpallant · 2026-03-20T14:58:12Z

cortex-m/macros/src/lib.rs

@@ -0,0 +1,57 @@
+//! Internal implementation details of `cortex-m-rt`.


Suggested change

//! Internal implementation details of `cortex-m-rt`.

//! Internal implementation details of `cortex-m`.

jonathanpallant · 2026-03-20T15:08:20Z

cortex-m/src/asm.rs

@@ -2,17 +2,22 @@

 // When inline assembly is enabled, pull in the assembly routines here. `call_asm!` will invoke


call_asm! doesn't exist any more

jonathanpallant · 2026-03-20T15:10:40Z

cortex-m/src/asm.rs


 /// A no-operation. Useful to prevent delay loops from being optimized away.
 #[inline]
+#[cortex_m_macros::asm_wrapper(any(armv6m, armv7m, armv7em, armv8m))]


Most of the public functions (in asm.rs) don't need #[asm_wrapper] on them, because they call inner functions which are wrapped with #[asm_wrapper]. So, even on non-cortex-m platforms, these functions will still compile.

jonathanpallant · 2026-03-20T15:11:06Z

cortex-m/src/asm.rs

-    call_asm!(__sh_syscall(nr: u32, arg: u32) -> u32)
+    let mut nr = nr;
+    unsafe {
+        asm!("bkpt #0xab", inout("r0") nr, in("r1") arg, options(nomem, nostack, preserves_flags))


I would move this inline assembly to the asm::inner module.

jonathanpallant · 2026-03-20T15:11:57Z

cortex-m/src/interrupt.rs

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


This is the public API for turning interrupts on and off - cpsie and cpsid are not exposed as individual functions.

jonathanpallant · 2026-03-20T15:13:02Z

cortex-m/src/asm/inner.rs

+
+    // Should this be safe?
+    #[inline(always)]
+    pub unsafe fn __enable_icache() {


The asm::inner functions should not start with __. That's just a hold-over from assembly code not having the concept of public/private symbols.

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

thejpster reviewed Mar 13, 2026

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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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wt added 2 commits March 17, 2026 21:45

Remove the precompiled functions wrapping assembly routines.

f22f532

wt force-pushed the update_asm_toolchain branch 7 times, most recently from fd3ccb5 to edb22b0 Compare March 18, 2026 07:03

wt force-pushed the update_asm_toolchain branch from edb22b0 to e53eba0 Compare March 18, 2026 08:23

Add asm_wrapper attribute.

63bee36

The purpose of this attribute is to allow platforms that do not support the asm instructions to compile code code that calls those functions. This is needed so that clippy can be run once in CI and when testing locally.

wt force-pushed the update_asm_toolchain branch from e53eba0 to 63bee36 Compare March 19, 2026 22:50

jonathanpallant requested changes Mar 20, 2026

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		@@ -0,0 +1,57 @@
		//! Internal implementation details of `cortex-m-rt`.

		@@ -2,17 +2,22 @@

		// When inline assembly is enabled, pull in the assembly routines here. `call_asm!` will invoke

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