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

[Ramiro Polla <ramiro.polla@gmail.com>]

On Tue, May 20, 2025 at 9:46 PM softworkz .
<softworkz-at-hotmail.com@ffmpeg.org> wrote:
> > -----Original Message-----
> > From: ffmpeg-devel <ffmpeg-devel-bounces@ffmpeg.org> On Behalf Of Ramiro Polla
> > Sent: Dienstag, 20. Mai 2025 21:36
> > To: FFmpeg development discussions and patches <ffmpeg-devel@ffmpeg.org>
> > Subject: Re: [FFmpeg-devel] [PATCH v2] ffbuild/commonmak: Fix rebuild check
> > with implicit rule chains
> > On Sun, May 18, 2025 at 8:30 AM softworkz <ffmpegagent@gmail.com> wrote:
> > > 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)/%,$<)
> > > +
> >
> > I'm not a big fan of adding new targets with a stripped-down version
> > of the original rule. It seems like unnecessary duplication, and
> > increases the chance of divergence over time.
> >
> > Instead, I think it's cleaner to use target-specific variables to
> > disable a part of the original rule. For example, in this case, you
> > would disable the dependency generation for just those targets, and
> > end up with something like this:
> > %.html.o: CC_DEPFLAGS =
> > %.css.o: CC_DEPFLAGS =
>
> Hi Ramiro,
>
> I didn't know that one can do that. That's clearly a better way, then.
>
> What about the first line in the COMPILE macro:
>
> define COMPILE
>        $(call $(1)DEP,$(1))
>        $($(1)) $($(1)FLAGS) $($(2)) $($(1)_DEPFLAGS) $($(1)_C) $($(1)_O) $(patsubst $(SRC_PATH)/%,$(SRC_LINK)/%,$<)
> endef
>
> I haven't traced back what it actually does - is it harmless when
> it's executed in those cases where no dependency file is desired?
>
> If that's fine, I'd send an updated patch with your suggestion.

I had forgotten about that part. It's not triggered with gcc/clang,
but it seems to be triggered when using msvc. I don't have an msvc
setup ready, but I believe you do, right? You can then check with
"make V=1".

Ramiro
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