rust: Use absolute paths to build Rust objects

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.

Signed-off-by: Asahi Lina <lina@asahilina.net>

Author: hoshinolina

rust/Makefile

@@ -339,7 +339,7 @@ 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 $<) \
 		--sysroot=/dev/null \
 	$(if $(rustc_objcopy),;$(OBJCOPY) $(rustc_objcopy) $@) \
 	$(cmd_objtool)

scripts/Makefile.build

@@ -273,7 +273,7 @@ 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_objtool)
+      cmd_rustc_o_rs = $(rust_common_cmd) --emit=obj=$@ $(abspath $<) $(cmd_objtool)
 
 define rule_rustc_o_rs
 	$(call cmd_and_fixdep,rustc_o_rs)
@@ -285,20 +285,20 @@ $(obj)/%.o: $(obj)/%.rs FORCE
 
 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: $(obj)/%.rs FORCE
 	+$(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: $(obj)/%.rs FORCE
 	+$(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: $(obj)/%.rs FORCE
 	+$(call if_changed_dep,rustc_ll_rs)