`rustc` outputs by default the temporary files (i.e. the ones saved
by `-Csave-temps`, such as `*.rcgu*` files) in the current working
directory when `-o` and `--out-dir` are not given (even if
`--emit=x=path` is given, i.e. it does not use those for temporaries).

Since out-of-tree modules are compiled from the `linux` tree,
`rustc` then tries to create them there, which may not be accessible.

Thus pass `--out-dir` explicitly, even if it is just for the temporary
files.

Similarly, do so for Rust host programs too.

Reported-by: Raphael Nestler <raphael.nestler@gmail.com>
Closes: https://github.com/Rust-for-Linux/linux/issues/1015
Reported-by: Andrea Righi <andrea.righi@canonical.com>
Tested-by: Raphael Nestler <raphael.nestler@gmail.com> # non-hostprogs
Tested-by: Andrea Righi <andrea.righi@canonical.com> # non-hostprogs
Fixes: 295d8398c67e ("kbuild: specify output names separately for each emission type from rustc")
Cc: stable@vger.kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
---
v2:
  - Add fix for host programs too (Masahiro).

 scripts/Makefile.build | 5 ++++-
 scripts/Makefile.host  | 6 +++++-
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 6413342a03f4..82e3fb19fdaf 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -264,6 +264,9 @@ $(obj)/%.lst: $(src)/%.c FORCE
 
 rust_allowed_features := new_uninit
 
+# `--out-dir` is required to avoid temporaries being created by `rustc` in the
+# current working directory, which may be not accessible in the out-of-tree
+# modules case.
 rust_common_cmd = \
 	RUST_MODFILE=$(modfile) $(RUSTC_OR_CLIPPY) $(rust_flags) \
 	-Zallow-features=$(rust_allowed_features) \
@@ -272,7 +275,7 @@ rust_common_cmd = \
 	--extern alloc --extern kernel \
 	--crate-type rlib -L $(objtree)/rust/ \
 	--crate-name $(basename $(notdir $@)) \
-	--emit=dep-info=$(depfile)
+	--out-dir $(dir $@) --emit=dep-info=$(depfile)
 
 # `--emit=obj`, `--emit=asm` and `--emit=llvm-ir` imply a single codegen unit
 # will be used. We explicitly request `-Ccodegen-units=1` in any case, and
diff --git a/scripts/Makefile.host b/scripts/Makefile.host
index 7aea9005e497..8f7f842b54f9 100644
--- a/scripts/Makefile.host
+++ b/scripts/Makefile.host
@@ -86,7 +86,11 @@ hostc_flags    = -Wp,-MMD,$(depfile) \
 hostcxx_flags  = -Wp,-MMD,$(depfile) \
                  $(KBUILD_HOSTCXXFLAGS) $(HOST_EXTRACXXFLAGS) \
                  $(HOSTCXXFLAGS_$(target-stem).o)
-hostrust_flags = --emit=dep-info=$(depfile) \
+
+# `--out-dir` is required to avoid temporaries being created by `rustc` in the
+# current working directory, which may be not accessible in the out-of-tree
+# modules case.
+hostrust_flags = --out-dir $(dir $@) --emit=dep-info=$(depfile) \
                  $(KBUILD_HOSTRUSTFLAGS) $(HOST_EXTRARUSTFLAGS) \
                  $(HOSTRUSTFLAGS_$(target-stem))
 

base-commit: 06c2afb862f9da8dc5efa4b6076a0e48c3fbaaa5
-- 
2.41.0

On Sun, Jul 23, 2023 at 11:21 PM Miguel Ojeda <ojeda@kernel.org> wrote:
>
> `rustc` outputs by default the temporary files (i.e. the ones saved
> by `-Csave-temps`, such as `*.rcgu*` files) in the current working
> directory when `-o` and `--out-dir` are not given (even if
> `--emit=x=path` is given, i.e. it does not use those for temporaries).
>
> Since out-of-tree modules are compiled from the `linux` tree,
> `rustc` then tries to create them there, which may not be accessible.
>
> Thus pass `--out-dir` explicitly, even if it is just for the temporary
> files.
>
> Similarly, do so for Rust host programs too.
>
> Reported-by: Raphael Nestler <raphael.nestler@gmail.com>
> Closes: https://github.com/Rust-for-Linux/linux/issues/1015
> Reported-by: Andrea Righi <andrea.righi@canonical.com>
> Tested-by: Raphael Nestler <raphael.nestler@gmail.com> # non-hostprogs
> Tested-by: Andrea Righi <andrea.righi@canonical.com> # non-hostprogs
> Fixes: 295d8398c67e ("kbuild: specify output names separately for each emission type from rustc")
> Cc: stable@vger.kernel.org
> Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
> ---
> v2:
>   - Add fix for host programs too (Masahiro).


This is now available in the mainline.

df01b7cfcef08bf3fdcac2909d0e1910781d6bfd





-- 
Best Regards
Masahiro Yamada

On 7/23/23 11:21, Miguel Ojeda wrote:
> `rustc` outputs by default the temporary files (i.e. the ones saved
> by `-Csave-temps`, such as `*.rcgu*` files) in the current working
> directory when `-o` and `--out-dir` are not given (even if
> `--emit=x=path` is given, i.e. it does not use those for temporaries).
> 
> Since out-of-tree modules are compiled from the `linux` tree,
> `rustc` then tries to create them there, which may not be accessible.
> 
> Thus pass `--out-dir` explicitly, even if it is just for the temporary
> files.
> 
> Similarly, do so for Rust host programs too.
> 
> Reported-by: Raphael Nestler <raphael.nestler@gmail.com>
> Closes: https://github.com/Rust-for-Linux/linux/issues/1015
> Reported-by: Andrea Righi <andrea.righi@canonical.com>
> Tested-by: Raphael Nestler <raphael.nestler@gmail.com> # non-hostprogs
> Tested-by: Andrea Righi <andrea.righi@canonical.com> # non-hostprogs
> Fixes: 295d8398c67e ("kbuild: specify output names separately for each emission type from rustc")
> Cc: stable@vger.kernel.org
> Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
> ---
> [...]
Tested-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>