linux-kernel - Re: [PATCH RFC 03/11] rust: Use absolute paths to build Rust objects

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Message-ID: <3de23cc5-ceef-555d-8a16-854f179705bc@asahilina.net>
Date:   Sun, 16 Jul 2023 16:53:57 +0900
From:   Asahi Lina <lina@...hilina.net>
To:     Gary Guo <gary@...yguo.net>
Cc:     Miguel Ojeda <ojeda@...nel.org>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Wedson Almeida Filho <wedsonaf@...il.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Björn Roy Baron <bjorn3_gh@...tonmail.com>,
        Benno Lossin <benno.lossin@...ton.me>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nicolas Schier <nicolas@...sle.eu>, Tom Rix <trix@...hat.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Hector Martin <marcan@...can.st>,
        Sven Peter <sven@...npeter.dev>,
        Alyssa Rosenzweig <alyssa@...enzweig.io>,
        asahi@...ts.linux.dev, rust-for-linux@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org,
        llvm@...ts.linux.dev
Subject: Re: [PATCH RFC 03/11] rust: Use absolute paths to build Rust objects

On 15/07/2023 23.35, Gary Guo wrote:
> On Fri, 14 Jul 2023 18:13:55 +0900
> Asahi Lina <lina@...hilina.net> wrote:
> 
>> We want to use caller_location to uniquely identify callsites, to
>> automatically create lockdep classes without macros. The location
>> filename in local code uses the relative path passed to the compiler,
>> but if that code is generic and instantiated from another crate, the
>> path becomes absolute.
>>
>> To make this work and keep the paths consistent, always pass an absolute
>> path to the compiler. Then the Location path is always identical
>> regardless of how the code is being compiled.
> 
> I wonder if this can have some reproducible build implications. We
> probably also need to use remap-path-prefix?

We already end up with absolute paths in objects anyway, just not 
consistently. If it were consistently relative paths that would be fine 
too, but it looks like Rust likes to internally absolute-ize some paths, 
that's why I wrote this patch to make it always like that.

TIL about remap-path-prefix, that looks very useful! I'll give it a try.

> 
>>
>> Signed-off-by: Asahi Lina <lina@...hilina.net>
>> ---
>>   rust/Makefile          | 2 +-
>>   scripts/Makefile.build | 8 ++++----
>>   2 files changed, 5 insertions(+), 5 deletions(-)
>>
>> diff --git a/rust/Makefile b/rust/Makefile
>> index 7c9d9f11aec5..552f023099c8 100644
>> --- a/rust/Makefile
>> +++ b/rust/Makefile
>> @@ -369,7 +369,7 @@ quiet_cmd_rustc_library = $(if $(skip_clippy),RUSTC,$(RUSTC_OR_CLIPPY_QUIET)) L
>>   		--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 $@)) $< \
>> +		--crate-name $(patsubst %.o,%,$(notdir $@)) $(abspath $<) \
>>   	$(if $(rustc_objcopy),;$(OBJCOPY) $(rustc_objcopy) $@)
>>   
>>   rust-analyzer:
>> diff --git a/scripts/Makefile.build b/scripts/Makefile.build
>> index 6413342a03f4..c925b90ebd80 100644
>> --- a/scripts/Makefile.build
>> +++ b/scripts/Makefile.build
>> @@ -283,27 +283,27 @@ rust_common_cmd = \
>>   # would not match each other.
>>   
>>   quiet_cmd_rustc_o_rs = $(RUSTC_OR_CLIPPY_QUIET) $(quiet_modtag) $@
>> -      cmd_rustc_o_rs = $(rust_common_cmd) --emit=obj=$@ $<
>> +      cmd_rustc_o_rs = $(rust_common_cmd) --emit=obj=$@ $(abspath $<)
>>   
>>   $(obj)/%.o: $(src)/%.rs FORCE
>>   	$(call if_changed_dep,rustc_o_rs)
>>   
>>   quiet_cmd_rustc_rsi_rs = $(RUSTC_OR_CLIPPY_QUIET) $(quiet_modtag) $@
>>         cmd_rustc_rsi_rs = \
>> -	$(rust_common_cmd) -Zunpretty=expanded $< >$@; \
>> +	$(rust_common_cmd) -Zunpretty=expanded $(abspath $<) >$@; \
>>   	command -v $(RUSTFMT) >/dev/null && $(RUSTFMT) $@
>>   
>>   $(obj)/%.rsi: $(src)/%.rs FORCE
>>   	$(call if_changed_dep,rustc_rsi_rs)
>>   
>>   quiet_cmd_rustc_s_rs = $(RUSTC_OR_CLIPPY_QUIET) $(quiet_modtag) $@
>> -      cmd_rustc_s_rs = $(rust_common_cmd) --emit=asm=$@ $<
>> +      cmd_rustc_s_rs = $(rust_common_cmd) --emit=asm=$@ $(abspath $<)
>>   
>>   $(obj)/%.s: $(src)/%.rs FORCE
>>   	$(call if_changed_dep,rustc_s_rs)
>>   
>>   quiet_cmd_rustc_ll_rs = $(RUSTC_OR_CLIPPY_QUIET) $(quiet_modtag) $@
>> -      cmd_rustc_ll_rs = $(rust_common_cmd) --emit=llvm-ir=$@ $<
>> +      cmd_rustc_ll_rs = $(rust_common_cmd) --emit=llvm-ir=$@ $(abspath $<)
>>   
>>   $(obj)/%.ll: $(src)/%.rs FORCE
>>   	$(call if_changed_dep,rustc_ll_rs)
>>
> 
> 

~~ Lina