Re: [FFmpeg-devel] [PATCH v2] ffbuild/commonmak: Fix rebuild check with implicit rule chains

["softworkz ." <softworkz-at-hotmail.com@ffmpeg.org>]

> -----Original Message-----
> From: softworkz <ffmpegagent@gmail.com>
> Sent: Sonntag, 18. Mai 2025 08:31
> To: ffmpeg-devel@ffmpeg.org
> Cc: softworkz <softworkz@hotmail.com>; softworkz <softworkz@hotmail.com>
> Subject: [PATCH v2] ffbuild/commonmak: Fix rebuild check with implicit rule
> chains
> 
> From: softworkz <softworkz@hotmail.com>
> 
> When there's a chain of implicit rules, make treats files generated
> inside that chain as intermediate files. Those intermediate files are
> removed after completion of make. When make is run again, it normally
> determines the need for a rebuild by comparing the timestamps of the
> original source file and the final output of the chain and if still
> up-to-date, it doesn't rebuild, even when the intermediate files are
> not present. That makes sense of course - why would it delete them
> otherwise, it would end up in builds being never up-to-date.
> But this original by-the-book logic appeared to be broken and has been
> worked around by adding all intermediate files to the .SECONDARY
> special target, which required extra logic and issues with make clean.
> 
> What broke the up-to-date checking is the dependency file generation.
> For the .c files generated by BIN2C the compile target created a .d
> file which indicated that the .ptx.o file has a dependency on the
> ptx.c file. And that dependency broke the normal make behavior with
> intermediate files.
> 
> This patch compiles the BIN2C generated .c files without generating
> .d files. In turn the files do not longer need to be added to the
> .SECONDARY target in common.mak.
> 
> When interested in those files for debugging, a line can be added to
> the corresponding Makefile like
> 
> .SECONDARY: %.ptx.c %.ptx.gz
> 
> Signed-off-by: softworkz <softworkz@hotmail.com>
> ---
>     ffbuild/commonmak: Fix rebuild check with implicit rule chains
> 
>     When there's a chain of implicit rules, make treats files generated
>     inside that chain as intermediate files. Those intermediate files are
>     removed after completion of make. When make is run again, it normally
>     determines the need for a rebuild by comparing the timestamps of the
>     original source file and the final output of the chain and if still
>     up-to-date, it doesn't rebuild, even when the intermediate files are not
>     present. That makes sense of course - why would it delete them
>     otherwise, it would end up in builds being never up-to-date. But this
>     original by-the-book logic appeared to be broken and has been worked
>     around by adding all intermediate files to the .SECONDARY special
>     target, which required extra logic and issues with make clean.
> 
>     What broke the up-to-date checking is the dependency file generation.
>     For the .c files generated by BIN2C the compile target created a .d file
>     which indicated that the .ptx.o file has a dependency on the ptx.c file.
>     And that dependency broke the normal make behavior with intermediate
>     files.
> 
>     This patch compiles the BIN2C generated .c files without generating .d
>     files. In turn the files do not longer need to be added to the
>     .SECONDARY target in common.mak.
> 
>     When interested in those files for debugging, a line can be added to the
>     corresponding Makefile like
> 
>     .SECONDARY: %.ptx.c %.ptx.gz
> 
> 
>     V2
>     ==
> 
>      * Fix MSVC build
>        (use the universal command pattern)
> 
> Published-As: https://github.com/ffstaging/FFmpeg/releases/tag/pr-ffstaging-
> 80%2Fsoftworkz%2Fsubmit_commonmak-v2
> Fetch-It-Via: git fetch https://github.com/ffstaging/FFmpeg pr-ffstaging-
> 80/softworkz/submit_commonmak-v2
> Pull-Request: https://github.com/ffstaging/FFmpeg/pull/80
> 
> Range-diff vs v1:
> 
>  1:  e276f54ffc ! 1:  f468ea2431 ffbuild/commonmak: Fix rebuild check with
> implicit rule chains
>      @@ ffbuild/common.mak: else
>        endif
> 
>       +%.ptx.o: %.ptx.c
>      -+	$(CC) $(CCFLAGS) -x c -c -o $@ $<
>      ++	$(CC) $(CCFLAGS) $(CC_C) $(CC_O) $(patsubst
> $(SRC_PATH)/%,$(SRC_LINK)/%,$<)
>       +
>       +
>        # 1) Preprocess CSS to a minified version
>      @@ ffbuild/common.mak: else   # NO COMPRESSION
>        endif
> 
>       +%.html.o: %.html.c
>      -+	$(CC) $(CCFLAGS) -x c -c -o $@ $<
>      ++	$(CC) $(CCFLAGS) $(CC_C) $(CC_O) $(patsubst
> $(SRC_PATH)/%,$(SRC_LINK)/%,$<)
>       +
>       +%.css.o: %.css.c
>      -+	$(CC) $(CCFLAGS) -x c -c -o $@ $<
>      ++	$(CC) $(CCFLAGS) $(CC_C) $(CC_O) $(patsubst
> $(SRC_PATH)/%,$(SRC_LINK)/%,$<)
>       +
>       +
>        clean::
> 
> 
>  ffbuild/common.mak | 15 ++++++++++++---
>  1 file changed, 12 insertions(+), 3 deletions(-)
> 
> diff --git a/ffbuild/common.mak b/ffbuild/common.mak
> index 0e1eb1f62b..d9462271d5 100644
> --- a/ffbuild/common.mak
> +++ b/ffbuild/common.mak
> @@ -139,6 +139,10 @@ else
>  	$(BIN2C) $(patsubst $(SRC_PATH)/%,$(SRC_LINK)/%,$<) $@ $(subst
> .,_,$(basename $(notdir $@)))
>  endif
> 
> +%.ptx.o: %.ptx.c
> +	$(CC) $(CCFLAGS) $(CC_C) $(CC_O) $(patsubst
> $(SRC_PATH)/%,$(SRC_LINK)/%,$<)
> +
> +
>  # 1) Preprocess CSS to a minified version
>  %.css.min: %.css
>  	# Must start with a tab in the real Makefile
> @@ -177,6 +181,13 @@ else   # NO COMPRESSION
>  	$(BIN2C) $< $@ $(subst .,_,$(basename $(notdir $@)))
>  endif
> 
> +%.html.o: %.html.c
> +	$(CC) $(CCFLAGS) $(CC_C) $(CC_O) $(patsubst
> $(SRC_PATH)/%,$(SRC_LINK)/%,$<)
> +
> +%.css.o: %.css.c
> +	$(CC) $(CCFLAGS) $(CC_C) $(CC_O) $(patsubst
> $(SRC_PATH)/%,$(SRC_LINK)/%,$<)
> +
> +
>  clean::
>  	$(RM) $(BIN2CEXE) $(CLEANSUFFIXES:%=ffbuild/%)
> 
> @@ -228,11 +239,9 @@ ALLHEADERS := $(subst $(SRC_DIR)/,$(SUBDIR),$(wildcard
> $(SRC_DIR)/*.h $(SRC_DIR)
>  SKIPHEADERS += $(ARCH_HEADERS:%=$(ARCH)/%) $(SKIPHEADERS-)
>  SKIPHEADERS := $(SKIPHEADERS:%=$(SUBDIR)%)
>  HOBJS        = $(filter-out $(SKIPHEADERS:.h=.h.o),$(ALLHEADERS:.h=.h.o))
> -PTXOBJS      = $(filter %.ptx.o,$(OBJS))
> -RESOURCEOBJS = $(filter %.css.o %.html.o,$(OBJS))
>  $(HOBJS):     CCFLAGS += $(CFLAGS_HEADERS)
>  checkheaders: $(HOBJS)
> -.SECONDARY:   $(HOBJS:.o=.c) $(PTXOBJS:.o=.c) $(PTXOBJS:.o=.gz)
> $(PTXOBJS:.o=) $(RESOURCEOBJS:.o=.c) $(RESOURCEOBJS:%.css.o=%.css.min)
> $(RESOURCEOBJS:%.css.o=%.css.min.gz) $(RESOURCEOBJS:%.html.o=%.html.gz)
> $(RESOURCEOBJS:.o=)
> +.SECONDARY:   $(HOBJS:.o=.c)
> 
>  alltools: $(TOOLS)
> 
> 
> base-commit: eb6dc952cbd479bf43673af9ca0bc83f37f8f329
> --


I just realized that I forgot to mention the specific problem that this
is addressing: Andreas and James had discovered that the up-to-date check
doesn't work properly - in a way that when you run make after make again,
it wants to rebuild the .o files from the BIN2C-generated .c files.

This patch fixes this by making it work in the way it is intended by make.
(https://www.gnu.org/software/make/manual/html_node/Chained-Rules.html) 

sw





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