[PATCH v2 2/2] kbuild: Use relative paths in generated .incbin directives

[Rasmus Villemoes]

On Fri, Mar 27 2026, Rasmus Villemoes <ravi at prevas.dk> wrote:

> On Thu, Mar 26 2026, Simon Glass <sjg at chromium.org> wrote:
>
>> The generated .S files for fonts and splash screens use .incbin with the
>> full prerequisite path. When building with O= this bakes an absolute
>> path into the .S file. If the build directory is later used on a
>> different machine (e.g. in a container), the assembler cannot find the
>> source file.
>
> I must be missing something, because I can't see how this can be a
> problem, while all the other absolute paths to the source dir that go
> into files generated in the build directory is not. For example, there's
> a top-level "source -> /path/to/u-boot" symlink created, and as far as I
> can tell, all the .foo.o.cmd files end up full of such references as
> well, e.g. $BUILD/lib/.vsprintf.o.cmd contains
>
> source_lib/vsprintf.o := /path/to/u-boot/lib/vsprintf.c

OK, I can sort-of reproduce, though I don't know if what I did is
representable for your use case. No containers involved, just moved the
source directory.

  # original source dir
  $ cd /tmp/u-boot 
  $ make O=/tmp/build sandbox_defconfig
  $ make O=/tmp/build -j7
  $ cd /tmp ; mv u-boot u-boot-new ; cd u-boot-new
  $ make O=/tmp/build -j7

This breaks as you describe, but most files simply get rebuilt due to
their .cmd files containing stale references to /tmp/u-boot/. Which
suggests that the bug is really the lack of a .S.cmd file describing how
the .S file was created in the first place.

This seems to be a better fix, which also causes the .S files to be
generated anew if one does some actual change to the rule:

diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 7386353e0cc..b2441080e7e 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -526,8 +526,8 @@ cmd_S_ttf=						\
 	echo '.balign 16';				\
 ) > $@
 
-$(obj)/%.S: $(src)/%.ttf
-	$(call cmd,S_ttf)
+$(obj)/%.S: $(src)/%.ttf FORCE
+	$(call if_changed,S_ttf)
 
 # Splash logos
 # ---------------------------------------------------------------------------
@@ -547,8 +547,8 @@ cmd_S_splash=						\
 	echo '.balign 16';				\
 ) > $@
 
-$(obj)/%.S: $(src)/%.bmp
-	$(call cmd,S_splash)
+$(obj)/%.S: $(src)/%.bmp FORCE
+	$(call if_changed,S_splash)
 
 # EFI applications
 # A Makefile target *.efi is built as EFI application.

See e.g. kernel commit a7f9241909 which did essentially the same change
to the .dtb -> .S rule back in 2018.

It still makes sense to put these rules in a u-boot specific makefile,
but this should avoid the need for each font .o file to need those
AFLAGS changes.

Rasmus