Re: [PATCH] rust: Makefile: apply fixed-x18 workaround only on arm64

Re: [PATCH] rust: Makefile: apply fixed-x18 workaround only on arm64

[Miguel Ojeda]

On Mon, Feb 2, 2026 at 3:39 PM HeeSu Kim <mlksvender@gmail.com> wrote:
>
> On Tue, Feb 03, 2026, Miguel Ojeda wrote:
> > Could you please elaborate on the issues you are seeing, e.g. how to
> > reproduce them?
> >
> > The flag is only used to silence errors from checks that were added to
> > `rustc` and it is ignored otherwise (that is why the workaround was
> > written like that).
>
> After reviewing my build logs, I found that the error I encountered was
> "unknown codegen option: -Cunsafe-allow-abi-mismatch" because I was
> using rustc 1.85 at the time. The flag was added in rustc 1.88.
>
> So this was not an architecture-specific issue. I apologize for the
> confusion and would like to withdraw this patch.

Thanks for reporting and double-checking, and no worries, it happens! :)

Cheers,
Miguel

Re: [PATCH] rust: Makefile: apply fixed-x18 workaround only on arm64

[HeeSu Kim]

On Tue, Feb 03, 2026, Miguel Ojeda wrote:
> Could you please elaborate on the issues you are seeing, e.g. how to
> reproduce them?
>
> The flag is only used to silence errors from checks that were added to
> `rustc` and it is ignored otherwise (that is why the workaround was
> written like that).

After reviewing my build logs, I found that the error I encountered was
"unknown codegen option: -Cunsafe-allow-abi-mismatch" because I was
using rustc 1.85 at the time. The flag was added in rustc 1.88.

So this was not an architecture-specific issue. I apologize for the
confusion and would like to withdraw this patch.

Best regards,
HeeSu Kim

Re: [PATCH] rust: Makefile: apply fixed-x18 workaround only on arm64

[HeeSu Kim]

On Tue, Feb 03, 2026, Gary Guo wrote:
> It looks like this bug has been fixed upstream already. While you're at
> it, would you mind also add code so that we stop applying the workaround
> for versions with bug fixed already?

Sure, I'll check which Rust version includes the fix and send a patch
with the requested changes.

Best regards,
HeeSu Kim

Re: [PATCH] rust: Makefile: apply fixed-x18 workaround only on arm64

[HeeSu Kim]

On Tue, Feb 03, 2026, C. Mitrodimas wrote:
> > The `-Cunsafe-allow-abi-mismatch=fixed-x18` option is a workaround for
> > a rustdoc issue (rust-lang/rust#144521) where target modifiers were not
> > properly saved. This affects both rustdoc and doctests builds.
> >
> > However, `fixed-x18` is an ARM64-specific ABI modifier related to the
> > x18 register reservation (used for Shadow Call Stack). Currently, this
> > workaround is applied unconditionally on all architectures, which is
> > incorrect and may cause issues on non-ARM64 builds.
> >
> > Restrict the workaround to only apply when building for arm64
> > (SRCARCH=arm64).
> >
> > Fixes: 68e8e79e1bdc ("rust: fix `rustdoc` target modifiers")
>
> Are we sure this is in the correct commit hash? It is not present on
> mainline.
>
> Maybe it should be this one?
>
>       Fixes: abbf9a449441 ("rust: workaround `rustdoc` target modifiers bug")
>
> Cheers,
> C. Mitrodimas

You're right. I mistakenly used a commit hash from my local branch.
I'll send a v2 with the correct Fixes tag.

[PATCH] rust: Makefile: apply fixed-x18 workaround only on arm64

[HeeSu Kim]

The `-Cunsafe-allow-abi-mismatch=fixed-x18` option is a workaround for
a rustdoc issue (rust-lang/rust#144521) where target modifiers were not
properly saved. This affects both rustdoc and doctests builds.

However, `fixed-x18` is an ARM64-specific ABI modifier related to the
x18 register reservation (used for Shadow Call Stack). Currently, this
workaround is applied unconditionally on all architectures, which is
incorrect and may cause issues on non-ARM64 builds.

Restrict the workaround to only apply when building for arm64
(SRCARCH=arm64).

Fixes: 68e8e79e1bdc ("rust: fix `rustdoc` target modifiers")
Signed-off-by: HeeSu Kim <mlksvender@gmail.com>
---
 rust/Makefile | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/rust/Makefile b/rust/Makefile
index 5c0155b83..2bd547611 100644
--- a/rust/Makefile
+++ b/rust/Makefile
@@ -136,7 +136,8 @@ pin_init-flags := \
 
 # `rustdoc` did not save the target modifiers, thus workaround for
 # the time being (https://github.com/rust-lang/rust/issues/144521).
-rustdoc_modifiers_workaround := $(if $(call rustc-min-version,108800),-Cunsafe-allow-abi-mismatch=fixed-x18)
+# The `fixed-x18` modifier is ARM64-specific, so only apply it there.
+rustdoc_modifiers_workaround := $(if $(filter arm64,$(SRCARCH)),$(if $(call rustc-min-version,108800),-Cunsafe-allow-abi-mismatch=fixed-x18))
 
 # Similarly, for doctests (https://github.com/rust-lang/rust/issues/146465).
 doctests_modifiers_workaround := $(rustdoc_modifiers_workaround)$(if $(call rustc-min-version,109100),$(comma)sanitizer)
-- 
2.52.0

Re: [PATCH] rust: Makefile: apply fixed-x18 workaround only on arm64

[Gary Guo]

On Mon Feb 2, 2026 at 10:21 PM GMT, HeeSu Kim wrote:
> The `-Cunsafe-allow-abi-mismatch=fixed-x18` option is a workaround for
> a rustdoc issue (rust-lang/rust#144521) where target modifiers were not
> properly saved. This affects both rustdoc and doctests builds.
>
> However, `fixed-x18` is an ARM64-specific ABI modifier related to the
> x18 register reservation (used for Shadow Call Stack). Currently, this
> workaround is applied unconditionally on all architectures, which is
> incorrect and may cause issues on non-ARM64 builds.
>
> Restrict the workaround to only apply when building for arm64
> (SRCARCH=arm64).
>
> Fixes: 68e8e79e1bdc ("rust: fix `rustdoc` target modifiers")
> Signed-off-by: HeeSu Kim <mlksvender@gmail.com>
> ---
>  rust/Makefile | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/rust/Makefile b/rust/Makefile
> index 5c0155b83..2bd547611 100644
> --- a/rust/Makefile
> +++ b/rust/Makefile
> @@ -136,7 +136,8 @@ pin_init-flags := \
>  
>  # `rustdoc` did not save the target modifiers, thus workaround for
>  # the time being (https://github.com/rust-lang/rust/issues/144521).
> -rustdoc_modifiers_workaround := $(if $(call rustc-min-version,108800),-Cunsafe-allow-abi-mismatch=fixed-x18)
> +# The `fixed-x18` modifier is ARM64-specific, so only apply it there.
> +rustdoc_modifiers_workaround := $(if $(filter arm64,$(SRCARCH)),$(if $(call rustc-min-version,108800),-Cunsafe-allow-abi-mismatch=fixed-x18))

It looks like this bug has been fixed upstream already. While you're at it,
would you mind also add code so that we stop applying the workaround for
versions with bug fixed already?

Thanks,
Gary

>  
>  # Similarly, for doctests (https://github.com/rust-lang/rust/issues/146465).
>  doctests_modifiers_workaround := $(rustdoc_modifiers_workaround)$(if $(call rustc-min-version,109100),$(comma)sanitizer)

Re: [PATCH] rust: Makefile: apply fixed-x18 workaround only on arm64

[Miguel Ojeda]

On Mon, Feb 2, 2026 at 2:21 PM HeeSu Kim <mlksvender@gmail.com> wrote:
>
> However, `fixed-x18` is an ARM64-specific ABI modifier related to the
> x18 register reservation (used for Shadow Call Stack). Currently, this
> workaround is applied unconditionally on all architectures, which is
> incorrect and may cause issues on non-ARM64 builds.

Could you please elaborate on the issues you are seeing, e.g. how to
reproduce them?

The flag is only used to silence errors from checks that were added to
`rustc` and it is ignored otherwise (that is why the workaround was
written like that).

Thank you!

Cheers,
Miguel

Re: [PATCH] rust: Makefile: apply fixed-x18 workaround only on arm64

[Charalampos Mitrodimas]

HeeSu Kim <mlksvender@gmail.com> writes:

> The `-Cunsafe-allow-abi-mismatch=fixed-x18` option is a workaround for
> a rustdoc issue (rust-lang/rust#144521) where target modifiers were not
> properly saved. This affects both rustdoc and doctests builds.
>
> However, `fixed-x18` is an ARM64-specific ABI modifier related to the
> x18 register reservation (used for Shadow Call Stack). Currently, this
> workaround is applied unconditionally on all architectures, which is
> incorrect and may cause issues on non-ARM64 builds.
>
> Restrict the workaround to only apply when building for arm64
> (SRCARCH=arm64).
>
> Fixes: 68e8e79e1bdc ("rust: fix `rustdoc` target modifiers")

Are we sure this is in the correct commit hash? It is not present on
mainline.

Maybe it should be this one?

      Fixes: abbf9a449441 ("rust: workaround `rustdoc` target modifiers bug")

Cheers,
C. Mitrodimas

> Signed-off-by: HeeSu Kim <mlksvender@gmail.com>
> ---
>  rust/Makefile | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/rust/Makefile b/rust/Makefile
> index 5c0155b83..2bd547611 100644
> --- a/rust/Makefile
> +++ b/rust/Makefile
> @@ -136,7 +136,8 @@ pin_init-flags := \
>  
>  # `rustdoc` did not save the target modifiers, thus workaround for
>  # the time being (https://github.com/rust-lang/rust/issues/144521).
> -rustdoc_modifiers_workaround := $(if $(call rustc-min-version,108800),-Cunsafe-allow-abi-mismatch=fixed-x18)
> +# The `fixed-x18` modifier is ARM64-specific, so only apply it there.
> +rustdoc_modifiers_workaround := $(if $(filter arm64,$(SRCARCH)),$(if
> $(call
> rustc-min-version,108800),-Cunsafe-allow-abi-mismatch=fixed-x18))
>  
>  # Similarly, for doctests (https://github.com/rust-lang/rust/issues/146465).
>  doctests_modifiers_workaround := $(rustdoc_modifiers_workaround)$(if
> $(call rustc-min-version,109100),$(comma)sanitizer)