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  3. [PATCH 0/6] kbuild: fix dep-file processing for rust
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[PATCH 1/6] kbuild: specify output names separately for each emission type from rustc

Masahiro Yamada posted 6 patches 2 years, 8 months ago
[PATCH 1/6] kbuild: specify output names separately for each emission type from rustc
Posted by Masahiro Yamada 2 years, 8 months ago 
In Kbuild, two different rules must not write to the same file, but
it happens when compiling rust source files.

For example, set CONFIG_SAMPLE_RUST_MINIMAL=m and run the following:

  $ make -j$(nproc) samples/rust/rust_minimal.o samples/rust/rust_minimal.rsi \
                    samples/rust/rust_minimal.s samples/rust/rust_minimal.ll
    [snip]
    RUSTC [M] samples/rust/rust_minimal.o
    RUSTC [M] samples/rust/rust_minimal.rsi
    RUSTC [M] samples/rust/rust_minimal.s
    RUSTC [M] samples/rust/rust_minimal.ll
  mv: cannot stat 'samples/rust/rust_minimal.d': No such file or directory
  make[3]: *** [scripts/Makefile.build:334: samples/rust/rust_minimal.ll] Error 1
  make[3]: *** Waiting for unfinished jobs....
  mv: cannot stat 'samples/rust/rust_minimal.d': No such file or directory
  make[3]: *** [scripts/Makefile.build:309: samples/rust/rust_minimal.o] Error 1
  mv: cannot stat 'samples/rust/rust_minimal.d': No such file or directory
  make[3]: *** [scripts/Makefile.build:326: samples/rust/rust_minimal.s] Error 1
  make[2]: *** [scripts/Makefile.build:504: samples/rust] Error 2
  make[1]: *** [scripts/Makefile.build:504: samples] Error 2
  make: *** [Makefile:2008: .] Error 2

The reason for the error is that 4 threads running in parallel creates
and renames the same file path, samples/rust/rust_minimal.d.

This does not happen when compiling C or assembly files because we
explicitly specify the dependency filename by using the preprocessor
option, -Wp,-MMD,$(depfile). $(depfile) is a unique path for each target.

Currently, rustc is only given --out-dir and the list of emitted types.
So, all the rust build rules output the dep-info into the default
<CRATE_NAME>.d, causing the conflict.

Fortunately, the --emit option is able to specify the output path
individually, with the form --emit=<type>=<path>.

Add --emit=dep-info=$(depfile) to the common command part. Also, remove
the redundant --out-dir because we specify the output path for each type.

The code gets much cleaner because we do not need to rename *.d files.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
---

 rust/Makefile          | 10 ++++------
 scripts/Makefile.build | 14 +++++++-------
 scripts/Makefile.host  |  9 +++------
 3 files changed, 14 insertions(+), 19 deletions(-)

diff --git a/rust/Makefile b/rust/Makefile
index ff70c4c916f8..0e2a32f4b3e9 100644
--- a/rust/Makefile
+++ b/rust/Makefile
@@ -331,10 +331,9 @@ $(obj)/exports_kernel_generated.h: $(obj)/kernel.o FORCE
 quiet_cmd_rustc_procmacro = $(RUSTC_OR_CLIPPY_QUIET) P $@
       cmd_rustc_procmacro = \
 	$(RUSTC_OR_CLIPPY) $(rust_common_flags) \
-		--emit=dep-info,link --extern proc_macro \
-		--crate-type proc-macro --out-dir $(objtree)/$(obj) \
+		--emit=dep-info=$(depfile) --emit=link=$@ --extern proc_macro \
+		--crate-type proc-macro \
 		--crate-name $(patsubst lib%.so,%,$(notdir $@)) $<; \
-	mv $(objtree)/$(obj)/$(patsubst lib%.so,%,$(notdir $@)).d $(depfile); \
 	sed -i '/^\#/d' $(depfile)
 
 # Procedural macros can only be used with the `rustc` that compiled it.
@@ -348,10 +347,9 @@ quiet_cmd_rustc_library = $(if $(skip_clippy),RUSTC,$(RUSTC_OR_CLIPPY_QUIET)) L
 	OBJTREE=$(abspath $(objtree)) \
 	$(if $(skip_clippy),$(RUSTC),$(RUSTC_OR_CLIPPY)) \
 		$(filter-out $(skip_flags),$(rust_flags) $(rustc_target_flags)) \
-		--emit=dep-info,obj,metadata --crate-type rlib \
-		--out-dir $(objtree)/$(obj) -L$(objtree)/$(obj) \
+		--emit=dep-info=$(depfile) --emit=obj=$@ --emit=metadata=$(dir $@)$(patsubst %.o,lib%.rmeta,$(notdir $@)) \
+		--crate-type rlib -L$(objtree)/$(obj) \
 		--crate-name $(patsubst %.o,%,$(notdir $@)) $<; \
-	mv $(objtree)/$(obj)/$(patsubst %.o,%,$(notdir $@)).d $(depfile); \
 	sed -i '/^\#/d' $(depfile) \
 	$(if $(rustc_objcopy),;$(OBJCOPY) $(rustc_objcopy) $@)
 
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index a0d5c6cca76d..40de20246e50 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -285,11 +285,11 @@ rust_common_cmd = \
 	-Zcrate-attr=no_std \
 	-Zcrate-attr='feature($(rust_allowed_features))' \
 	--extern alloc --extern kernel \
-	--crate-type rlib --out-dir $(obj) -L $(objtree)/rust/ \
-	--crate-name $(basename $(notdir $@))
+	--crate-type rlib -L $(objtree)/rust/ \
+	--crate-name $(basename $(notdir $@)) \
+	--emit=dep-info=$(depfile)
 
 rust_handle_depfile = \
-	mv $(obj)/$(basename $(notdir $@)).d $(depfile); \
 	sed -i '/^\#/d' $(depfile)
 
 # `--emit=obj`, `--emit=asm` and `--emit=llvm-ir` imply a single codegen unit
@@ -302,7 +302,7 @@ rust_handle_depfile = \
 
 quiet_cmd_rustc_o_rs = $(RUSTC_OR_CLIPPY_QUIET) $(quiet_modtag) $@
       cmd_rustc_o_rs = \
-	$(rust_common_cmd) --emit=dep-info,obj $<; \
+	$(rust_common_cmd) --emit=obj=$@ $<; \
 	$(rust_handle_depfile)
 
 $(obj)/%.o: $(src)/%.rs FORCE
@@ -310,7 +310,7 @@ $(obj)/%.o: $(src)/%.rs FORCE
 
 quiet_cmd_rustc_rsi_rs = $(RUSTC_OR_CLIPPY_QUIET) $(quiet_modtag) $@
       cmd_rustc_rsi_rs = \
-	$(rust_common_cmd) --emit=dep-info -Zunpretty=expanded $< >$@; \
+	$(rust_common_cmd) -Zunpretty=expanded $< >$@; \
 	command -v $(RUSTFMT) >/dev/null && $(RUSTFMT) $@; \
 	$(rust_handle_depfile)
 
@@ -319,7 +319,7 @@ $(obj)/%.rsi: $(src)/%.rs FORCE
 
 quiet_cmd_rustc_s_rs = $(RUSTC_OR_CLIPPY_QUIET) $(quiet_modtag) $@
       cmd_rustc_s_rs = \
-	$(rust_common_cmd) --emit=dep-info,asm $<; \
+	$(rust_common_cmd) --emit=asm=$@ $<; \
 	$(rust_handle_depfile)
 
 $(obj)/%.s: $(src)/%.rs FORCE
@@ -327,7 +327,7 @@ $(obj)/%.s: $(src)/%.rs FORCE
 
 quiet_cmd_rustc_ll_rs = $(RUSTC_OR_CLIPPY_QUIET) $(quiet_modtag) $@
       cmd_rustc_ll_rs = \
-	$(rust_common_cmd) --emit=dep-info,llvm-ir $<; \
+	$(rust_common_cmd) --emit=llvm-ir=$@ $<; \
 	$(rust_handle_depfile)
 
 $(obj)/%.ll: $(src)/%.rs FORCE
diff --git a/scripts/Makefile.host b/scripts/Makefile.host
index da133780b751..4434cdbf7b8e 100644
--- a/scripts/Makefile.host
+++ b/scripts/Makefile.host
@@ -84,8 +84,8 @@ _hostc_flags   = $(KBUILD_HOSTCFLAGS)   $(HOST_EXTRACFLAGS)   \
                  $(HOSTCFLAGS_$(target-stem).o)
 _hostcxx_flags = $(KBUILD_HOSTCXXFLAGS) $(HOST_EXTRACXXFLAGS) \
                  $(HOSTCXXFLAGS_$(target-stem).o)
-_hostrust_flags = $(KBUILD_HOSTRUSTFLAGS) $(HOST_EXTRARUSTFLAGS) \
-                  $(HOSTRUSTFLAGS_$(target-stem))
+hostrust_flags = $(KBUILD_HOSTRUSTFLAGS) $(HOST_EXTRARUSTFLAGS) \
+                  $(HOSTRUSTFLAGS_$(target-stem)) --emit=dep-info=$(depfile)
 
 # $(objtree)/$(obj) for including generated headers from checkin source files
 ifeq ($(KBUILD_EXTMOD),)
@@ -97,7 +97,6 @@ endif
 
 hostc_flags    = -Wp,-MMD,$(depfile) $(_hostc_flags)
 hostcxx_flags  = -Wp,-MMD,$(depfile) $(_hostcxx_flags)
-hostrust_flags = $(_hostrust_flags)
 
 #####
 # Compile programs on the host
@@ -149,9 +148,7 @@ $(host-cxxobjs): $(obj)/%.o: $(src)/%.cc FORCE
 # host-rust -> Executable
 quiet_cmd_host-rust	= HOSTRUSTC $@
       cmd_host-rust	= \
-	$(HOSTRUSTC) $(hostrust_flags) --emit=dep-info,link \
-		--out-dir=$(obj)/ $<; \
-	mv $(obj)/$(target-stem).d $(depfile); \
+	$(HOSTRUSTC) $(hostrust_flags) --emit=link=$@ $<; \
 	sed -i '/^\#/d' $(depfile)
 $(host-rust): $(obj)/%: $(src)/%.rs FORCE
 	$(call if_changed_dep,host-rust)
-- 
2.34.1
Re: [PATCH 1/6] kbuild: specify output names separately for each emission type from rustc
Posted by Vincenzo 2 years, 8 months ago 
Reviewed-by: Vincenzo Palazzo <vincenzopalazzodev@gmail.com>


On Sat Dec 31, 2022 at 7:41 AM CET, Masahiro Yamada wrote:
> In Kbuild, two different rules must not write to the same file, but
> it happens when compiling rust source files.
>
> For example, set CONFIG_SAMPLE_RUST_MINIMAL=m and run the following:
>
>   $ make -j$(nproc) samples/rust/rust_minimal.o samples/rust/rust_minimal.rsi \
>                     samples/rust/rust_minimal.s samples/rust/rust_minimal.ll
>     [snip]
>     RUSTC [M] samples/rust/rust_minimal.o
>     RUSTC [M] samples/rust/rust_minimal.rsi
>     RUSTC [M] samples/rust/rust_minimal.s
>     RUSTC [M] samples/rust/rust_minimal.ll
>   mv: cannot stat 'samples/rust/rust_minimal.d': No such file or directory
>   make[3]: *** [scripts/Makefile.build:334: samples/rust/rust_minimal.ll] Error 1
>   make[3]: *** Waiting for unfinished jobs....
>   mv: cannot stat 'samples/rust/rust_minimal.d': No such file or directory
>   make[3]: *** [scripts/Makefile.build:309: samples/rust/rust_minimal.o] Error 1
>   mv: cannot stat 'samples/rust/rust_minimal.d': No such file or directory
>   make[3]: *** [scripts/Makefile.build:326: samples/rust/rust_minimal.s] Error 1
>   make[2]: *** [scripts/Makefile.build:504: samples/rust] Error 2
>   make[1]: *** [scripts/Makefile.build:504: samples] Error 2
>   make: *** [Makefile:2008: .] Error 2
>
> The reason for the error is that 4 threads running in parallel creates
> and renames the same file path, samples/rust/rust_minimal.d.
>
> This does not happen when compiling C or assembly files because we
> explicitly specify the dependency filename by using the preprocessor
> option, -Wp,-MMD,$(depfile). $(depfile) is a unique path for each target.
>
> Currently, rustc is only given --out-dir and the list of emitted types.
> So, all the rust build rules output the dep-info into the default
> <CRATE_NAME>.d, causing the conflict.
>
> Fortunately, the --emit option is able to specify the output path
> individually, with the form --emit=<type>=<path>.
>
> Add --emit=dep-info=$(depfile) to the common command part. Also, remove
> the redundant --out-dir because we specify the output path for each type.
>
> The code gets much cleaner because we do not need to rename *.d files.
>
> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
> ---
>
>  rust/Makefile          | 10 ++++------
>  scripts/Makefile.build | 14 +++++++-------
>  scripts/Makefile.host  |  9 +++------
>  3 files changed, 14 insertions(+), 19 deletions(-)
>
> diff --git a/rust/Makefile b/rust/Makefile
> index ff70c4c916f8..0e2a32f4b3e9 100644
> --- a/rust/Makefile
> +++ b/rust/Makefile
> @@ -331,10 +331,9 @@ $(obj)/exports_kernel_generated.h: $(obj)/kernel.o FORCE
>  quiet_cmd_rustc_procmacro = $(RUSTC_OR_CLIPPY_QUIET) P $@
>        cmd_rustc_procmacro = \
>  	$(RUSTC_OR_CLIPPY) $(rust_common_flags) \
> -		--emit=dep-info,link --extern proc_macro \
> -		--crate-type proc-macro --out-dir $(objtree)/$(obj) \
> +		--emit=dep-info=$(depfile) --emit=link=$@ --extern proc_macro \
> +		--crate-type proc-macro \
>  		--crate-name $(patsubst lib%.so,%,$(notdir $@)) $<; \
> -	mv $(objtree)/$(obj)/$(patsubst lib%.so,%,$(notdir $@)).d $(depfile); \
>  	sed -i '/^\#/d' $(depfile)
>  
>  # Procedural macros can only be used with the `rustc` that compiled it.
> @@ -348,10 +347,9 @@ quiet_cmd_rustc_library = $(if $(skip_clippy),RUSTC,$(RUSTC_OR_CLIPPY_QUIET)) L
>  	OBJTREE=$(abspath $(objtree)) \
>  	$(if $(skip_clippy),$(RUSTC),$(RUSTC_OR_CLIPPY)) \
>  		$(filter-out $(skip_flags),$(rust_flags) $(rustc_target_flags)) \
> -		--emit=dep-info,obj,metadata --crate-type rlib \
> -		--out-dir $(objtree)/$(obj) -L$(objtree)/$(obj) \
> +		--emit=dep-info=$(depfile) --emit=obj=$@ --emit=metadata=$(dir $@)$(patsubst %.o,lib%.rmeta,$(notdir $@)) \
> +		--crate-type rlib -L$(objtree)/$(obj) \
>  		--crate-name $(patsubst %.o,%,$(notdir $@)) $<; \
> -	mv $(objtree)/$(obj)/$(patsubst %.o,%,$(notdir $@)).d $(depfile); \
>  	sed -i '/^\#/d' $(depfile) \
>  	$(if $(rustc_objcopy),;$(OBJCOPY) $(rustc_objcopy) $@)
>  
> diff --git a/scripts/Makefile.build b/scripts/Makefile.build
> index a0d5c6cca76d..40de20246e50 100644
> --- a/scripts/Makefile.build
> +++ b/scripts/Makefile.build
> @@ -285,11 +285,11 @@ rust_common_cmd = \
>  	-Zcrate-attr=no_std \
>  	-Zcrate-attr='feature($(rust_allowed_features))' \
>  	--extern alloc --extern kernel \
> -	--crate-type rlib --out-dir $(obj) -L $(objtree)/rust/ \
> -	--crate-name $(basename $(notdir $@))
> +	--crate-type rlib -L $(objtree)/rust/ \
> +	--crate-name $(basename $(notdir $@)) \
> +	--emit=dep-info=$(depfile)
>  
>  rust_handle_depfile = \
> -	mv $(obj)/$(basename $(notdir $@)).d $(depfile); \
>  	sed -i '/^\#/d' $(depfile)
>  
>  # `--emit=obj`, `--emit=asm` and `--emit=llvm-ir` imply a single codegen unit
> @@ -302,7 +302,7 @@ rust_handle_depfile = \
>  
>  quiet_cmd_rustc_o_rs = $(RUSTC_OR_CLIPPY_QUIET) $(quiet_modtag) $@
>        cmd_rustc_o_rs = \
> -	$(rust_common_cmd) --emit=dep-info,obj $<; \
> +	$(rust_common_cmd) --emit=obj=$@ $<; \
>  	$(rust_handle_depfile)
>  
>  $(obj)/%.o: $(src)/%.rs FORCE
> @@ -310,7 +310,7 @@ $(obj)/%.o: $(src)/%.rs FORCE
>  
>  quiet_cmd_rustc_rsi_rs = $(RUSTC_OR_CLIPPY_QUIET) $(quiet_modtag) $@
>        cmd_rustc_rsi_rs = \
> -	$(rust_common_cmd) --emit=dep-info -Zunpretty=expanded $< >$@; \
> +	$(rust_common_cmd) -Zunpretty=expanded $< >$@; \
>  	command -v $(RUSTFMT) >/dev/null && $(RUSTFMT) $@; \
>  	$(rust_handle_depfile)
>  
> @@ -319,7 +319,7 @@ $(obj)/%.rsi: $(src)/%.rs FORCE
>  
>  quiet_cmd_rustc_s_rs = $(RUSTC_OR_CLIPPY_QUIET) $(quiet_modtag) $@
>        cmd_rustc_s_rs = \
> -	$(rust_common_cmd) --emit=dep-info,asm $<; \
> +	$(rust_common_cmd) --emit=asm=$@ $<; \
>  	$(rust_handle_depfile)
>  
>  $(obj)/%.s: $(src)/%.rs FORCE
> @@ -327,7 +327,7 @@ $(obj)/%.s: $(src)/%.rs FORCE
>  
>  quiet_cmd_rustc_ll_rs = $(RUSTC_OR_CLIPPY_QUIET) $(quiet_modtag) $@
>        cmd_rustc_ll_rs = \
> -	$(rust_common_cmd) --emit=dep-info,llvm-ir $<; \
> +	$(rust_common_cmd) --emit=llvm-ir=$@ $<; \
>  	$(rust_handle_depfile)
>  
>  $(obj)/%.ll: $(src)/%.rs FORCE
> diff --git a/scripts/Makefile.host b/scripts/Makefile.host
> index da133780b751..4434cdbf7b8e 100644
> --- a/scripts/Makefile.host
> +++ b/scripts/Makefile.host
> @@ -84,8 +84,8 @@ _hostc_flags   = $(KBUILD_HOSTCFLAGS)   $(HOST_EXTRACFLAGS)   \
>                   $(HOSTCFLAGS_$(target-stem).o)
>  _hostcxx_flags = $(KBUILD_HOSTCXXFLAGS) $(HOST_EXTRACXXFLAGS) \
>                   $(HOSTCXXFLAGS_$(target-stem).o)
> -_hostrust_flags = $(KBUILD_HOSTRUSTFLAGS) $(HOST_EXTRARUSTFLAGS) \
> -                  $(HOSTRUSTFLAGS_$(target-stem))
> +hostrust_flags = $(KBUILD_HOSTRUSTFLAGS) $(HOST_EXTRARUSTFLAGS) \
> +                  $(HOSTRUSTFLAGS_$(target-stem)) --emit=dep-info=$(depfile)
>  
>  # $(objtree)/$(obj) for including generated headers from checkin source files
>  ifeq ($(KBUILD_EXTMOD),)
> @@ -97,7 +97,6 @@ endif
>  
>  hostc_flags    = -Wp,-MMD,$(depfile) $(_hostc_flags)
>  hostcxx_flags  = -Wp,-MMD,$(depfile) $(_hostcxx_flags)
> -hostrust_flags = $(_hostrust_flags)
>  
>  #####
>  # Compile programs on the host
> @@ -149,9 +148,7 @@ $(host-cxxobjs): $(obj)/%.o: $(src)/%.cc FORCE
>  # host-rust -> Executable
>  quiet_cmd_host-rust	= HOSTRUSTC $@
>        cmd_host-rust	= \
> -	$(HOSTRUSTC) $(hostrust_flags) --emit=dep-info,link \
> -		--out-dir=$(obj)/ $<; \
> -	mv $(obj)/$(target-stem).d $(depfile); \
> +	$(HOSTRUSTC) $(hostrust_flags) --emit=link=$@ $<; \
>  	sed -i '/^\#/d' $(depfile)
>  $(host-rust): $(obj)/%: $(src)/%.rs FORCE
>  	$(call if_changed_dep,host-rust)
> -- 
> 2.34.1
Re: [PATCH 1/6] kbuild: specify output names separately for each emission type from rustc
Posted by Miguel Ojeda 2 years, 8 months ago 
On Sat, Dec 31, 2022 at 7:42 AM Masahiro Yamada <masahiroy@kernel.org> wrote:
>
>   $ make -j$(nproc) samples/rust/rust_minimal.o samples/rust/rust_minimal.rsi \
>                     samples/rust/rust_minimal.s samples/rust/rust_minimal.ll

Yeah, we were testing the single targets, but not multiple at once, thanks!

> +               --emit=dep-info=$(depfile) --emit=obj=$@ --emit=metadata=$(dir $@)$(patsubst %.o,lib%.rmeta,$(notdir $@)) \

Perhaps a newline here to avoid the lengthy line?

>  hostc_flags    = -Wp,-MMD,$(depfile) $(_hostc_flags)
>  hostcxx_flags  = -Wp,-MMD,$(depfile) $(_hostcxx_flags)
> -hostrust_flags = $(_hostrust_flags)

This was originally meant to be consistent with C and C++ indeed, but
if you prefer less variables, I guess it is fine, in which case,
should we update the C/C++ side too (in another series)?

Reviewed-by: Miguel Ojeda <ojeda@kernel.org>
Tested-by: Miguel Ojeda <ojeda@kernel.org>

Cheers,
Miguel
Re: [PATCH 1/6] kbuild: specify output names separately for each emission type from rustc
Posted by Masahiro Yamada 2 years, 8 months ago 
On Wed, Jan 4, 2023 at 5:45 AM Miguel Ojeda
<miguel.ojeda.sandonis@gmail.com> wrote:
>
> On Sat, Dec 31, 2022 at 7:42 AM Masahiro Yamada <masahiroy@kernel.org> wrote:
> >
> >   $ make -j$(nproc) samples/rust/rust_minimal.o samples/rust/rust_minimal.rsi \
> >                     samples/rust/rust_minimal.s samples/rust/rust_minimal.ll
>
> Yeah, we were testing the single targets, but not multiple at once, thanks!
>
> > +               --emit=dep-info=$(depfile) --emit=obj=$@ --emit=metadata=$(dir $@)$(patsubst %.o,lib%.rmeta,$(notdir $@)) \
>
> Perhaps a newline here to avoid the lengthy line?


OK, I will wrap it in v2.


>
> >  hostc_flags    = -Wp,-MMD,$(depfile) $(_hostc_flags)
> >  hostcxx_flags  = -Wp,-MMD,$(depfile) $(_hostcxx_flags)
> > -hostrust_flags = $(_hostrust_flags)
>
> This was originally meant to be consistent with C and C++ indeed, but
> if you prefer less variables, I guess it is fine, in which case,
> should we update the C/C++ side too (in another series)?


Yup, we could do this with less variables.
I will send a clean up.


> Reviewed-by: Miguel Ojeda <ojeda@kernel.org>
> Tested-by: Miguel Ojeda <ojeda@kernel.org>
>
> Cheers,
> Miguel



-- 
Best Regards
Masahiro Yamada
Re: [PATCH 1/6] kbuild: specify output names separately for each emission type from rustc
Posted by Gary Guo 2 years, 8 months ago 
On Sat, 31 Dec 2022 15:41:58 +0900
Masahiro Yamada <masahiroy@kernel.org> wrote:

> diff --git a/scripts/Makefile.host b/scripts/Makefile.host
> index da133780b751..4434cdbf7b8e 100644
> --- a/scripts/Makefile.host
> +++ b/scripts/Makefile.host
> @@ -84,8 +84,8 @@ _hostc_flags   = $(KBUILD_HOSTCFLAGS)   $(HOST_EXTRACFLAGS)   \
>                   $(HOSTCFLAGS_$(target-stem).o)
>  _hostcxx_flags = $(KBUILD_HOSTCXXFLAGS) $(HOST_EXTRACXXFLAGS) \
>                   $(HOSTCXXFLAGS_$(target-stem).o)
> -_hostrust_flags = $(KBUILD_HOSTRUSTFLAGS) $(HOST_EXTRARUSTFLAGS) \
> -                  $(HOSTRUSTFLAGS_$(target-stem))
> +hostrust_flags = $(KBUILD_HOSTRUSTFLAGS) $(HOST_EXTRARUSTFLAGS) \
> +                  $(HOSTRUSTFLAGS_$(target-stem)) --emit=dep-info=$(depfile)
>  
>  # $(objtree)/$(obj) for including generated headers from checkin source files
>  ifeq ($(KBUILD_EXTMOD),)
> @@ -97,7 +97,6 @@ endif
>  
>  hostc_flags    = -Wp,-MMD,$(depfile) $(_hostc_flags)
>  hostcxx_flags  = -Wp,-MMD,$(depfile) $(_hostcxx_flags)
> -hostrust_flags = $(_hostrust_flags)

Would it be better to have `--emit=dep-info=$(depfile)` added here
instead so that it mimics c/cxx flags?

>  
>  #####
>  # Compile programs on the host
> @@ -149,9 +148,7 @@ $(host-cxxobjs): $(obj)/%.o: $(src)/%.cc FORCE
>  # host-rust -> Executable
>  quiet_cmd_host-rust	= HOSTRUSTC $@
>        cmd_host-rust	= \
> -	$(HOSTRUSTC) $(hostrust_flags) --emit=dep-info,link \
> -		--out-dir=$(obj)/ $<; \
> -	mv $(obj)/$(target-stem).d $(depfile); \
> +	$(HOSTRUSTC) $(hostrust_flags) --emit=link=$@ $<; \
>  	sed -i '/^\#/d' $(depfile)
>  $(host-rust): $(obj)/%: $(src)/%.rs FORCE
>  	$(call if_changed_dep,host-rust)

Best,
Gary

Patchew 2.1-devel-b67e4c2

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