[PATCH v2] kbuild, rust: use -fremap-path-prefix to make paths relative

["Thomas Weißschuh" <linux@weissschuh.net>]

Remap source path prefixes in all output, including compiler
diagnostics, debug information, macro expansions, etc.
This removes a few absolute paths from the binary and also makes it
possible to use core::panic::Location properly.

Equivalent to the same configuration done for C sources in
commit 1d3730f0012f ("kbuild: support -fmacro-prefix-map for external modules")
and commit a73619a845d5 ("kbuild: use -fmacro-prefix-map to make __FILE__ a relative path").

Link: https://doc.rust-lang.org/rustc/command-line-arguments.html#--remap-path-prefix-remap-source-names-in-output
Acked-by: Miguel Ojeda <ojeda@kernel.org>
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
---
Changes in v2:
- Drop the usage of $(call rustc-option)
- Link to v1: https://lore.kernel.org/r/20250210-rust-path-remap-v1-1-021c48188df1@weissschuh.net
---
 Makefile | 1 +
 1 file changed, 1 insertion(+)

diff --git a/Makefile b/Makefile
index 9e0d63d9d94b90672f91929e5e148e5a0c346cb6..9ed2222fafd4fa37a367b87a5c681936368318e7 100644
--- a/Makefile
+++ b/Makefile
@@ -1068,6 +1068,7 @@ endif
 # change __FILE__ to the relative path to the source directory
 ifdef building_out_of_srctree
 KBUILD_CPPFLAGS += $(call cc-option,-fmacro-prefix-map=$(srcroot)/=)
+KBUILD_RUSTFLAGS += --remap-path-prefix=$(srcroot)/=
 endif
 
 # include additional Makefiles when needed

---
base-commit: beeb78d46249cab8b2b8359a2ce8fa5376b5ad2d
change-id: 20250210-rust-path-remap-e97cec71e61a

Best regards,
-- 
Thomas Weißschuh <linux@weissschuh.net>