Patrick Georgi has submitted this change and it was merged. ( https://review.coreboot.org/28197 )
Change subject: Makefile.inc: Ensure update of build.h ......................................................................
Makefile.inc: Ensure update of build.h
There were so many pitfalls that I wrote my own version of this even- tually. This version is inspired by the procedure of Alex Thiessen[1]. Instead of generating a `build.h` on demand, we always generate a tem- porary version that, if it differs from the current one, is added as a dependency.
As we use .SECONDEXPANSION on the prerequisites, special care is taken that we won't generate the file twice. As it would be too late to add the dependency if we'd run `genbuild_h.sh` inside a recipe, we have to run it through the `$(shell)` function. But that brings us to the next issue: The make variables used by `genbuild_h.sh` are not expor- ted to this shell like they would be in a recipe. So we export them manually. We could also make these variables explicit parameters of `genbuild_h.sh` instead.
An alternative to always creating the temporary `build.h` would be to add a phony target as dependency instead, and finally calling `genbuild_h.sh` again in case we need an update. But, um, we create so many files anyway...
[1] https://review.coreboot.org/25685
Change-Id: I311cf610eabae873c70f2985fc7a09acec8061f0 Signed-off-by: Nico Huber nico.h@gmx.de Reviewed-on: https://review.coreboot.org/28197 Tested-by: build bot (Jenkins) no-reply@coreboot.org Reviewed-by: Patrick Rudolph siro@das-labor.org --- M Makefile.inc 1 file changed, 17 insertions(+), 4 deletions(-)
Approvals: build bot (Jenkins): Verified Patrick Rudolph: Looks good to me, approved
diff --git a/Makefile.inc b/Makefile.inc index 7ce2360..3840505 100644 --- a/Makefile.inc +++ b/Makefile.inc @@ -464,11 +464,24 @@
####################################################################### # generate build support files -$(obj)/build.h: .xcompile + +build_h := $(obj)/build.h + +# We have to manually export variables that `genbuild_h.sh` uses +# when we call it through the `$(shell)` function. This is fragile +# but as variables newly added to `genbuild_h.sh` would just not +# work, we'd notice that instantly at least. +build_h_exports := BUILD_TIMELESS KERNELVERSION COREBOOT_EXTRA_VERSION + +# Report new `build.ht` as dependency if `build.h` differs. +build_h_check := \ + export $(foreach exp,$(build_h_exports),$(exp)="$($(exp))"); \ + util/genbuild_h/genbuild_h.sh >$(build_h)t 2>/dev/null; \ + cmp -s $(build_h)t $(build_h) >/dev/null 2>&1 || echo $(build_h)t + +$(build_h): $$(shell $$(build_h_check)) @printf " GEN build.h\n" - rm -f $(obj)/build.h - util/genbuild_h/genbuild_h.sh > $(obj)/build.ht - mv $(obj)/build.ht $(obj)/build.h + mv $< $@
build-dirs: mkdir -p $(objcbfs) $(objgenerated)