[PATCH 1/2] Makefile: limit make re-execution to avoid infinite spin

[PATCH 1/2] Makefile: limit make re-execution to avoid infinite spin

[Sergei Trofimovich]

make-4.4 became intentionally more eager at rebuilding outdated Makefile
includes. Currently this causes `dtc` to spin infinitely in
parser/dependency loop:

    $ make
    ...
        CHK version_gen.h
         BISON dtc-parser.tab.h
         DEP dtc-lexer.lex.c
         DEP dtc-parser.tab.c
        CHK version_gen.h
         BISON dtc-parser.tab.h
         DEP dtc-lexer.lex.c
         DEP dtc-parser.tab.c
    ... # never stops

After the change build eventually fails when gets into this state:

    $ make
    ...
        CHK version_gen.h
        UPD version_gen.h
         DEP util.c
         BISON dtc-parser.tab.h
         DEP dtc-lexer.lex.c
         DEP dtc-parser.tab.c
        CHK version_gen.h
         BISON dtc-parser.tab.h
         DEP dtc-lexer.lex.c
         DEP dtc-parser.tab.c
    Makefile:394: *** "Make re-executed itself 10 times. Infinite recursion?".  Stop.

The actual recursion will be fixed separately.

Signed-off-by: Sergei Trofimovich <slyich-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
---
 Makefile | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/Makefile b/Makefile
index 9f1223f..e7a0dcb 100644
--- a/Makefile
+++ b/Makefile
@@ -389,3 +389,7 @@ clean: libfdt_clean pylibfdt_clean tests_clean
 	$(BISON) -b $(basename $(basename $@)) -d $<
 
 FORCE:
+
+ifeq ($(MAKE_RESTARTS),10)
+$(error "Make re-executed itself $(MAKE_RESTARTS) times. Infinite recursion?")
+endif
-- 
2.37.2

[PATCH 2/2] Makefile: fix infinite recursion by dropping non-existent `%.output`

[Sergei Trofimovich]

Without the change GNU `make-4.4` falls into infinite recursion of trying
to generate %.output files (bison is not passed flags to generate debug
output).

This happens on GNU `make-4.4` only after GNU make change to more eagerly
rebuild all target outputs in multiple targets:
    https://savannah.gnu.org/bugs/index.php?63098

The recursion here is the following:

- Makefile depends on *.d files
- *.d files depend on *.c files
- *.c files are generated by bison
- bison is triggered whenever some of it's multiple targets are missing

In our case `%.output` is always missing and bison is always reran.
*.d files are always regenerated on `make` run. And make is always
restarted as *.d files are always regenerated.

The fix removes infeasible `%.output`.

Signed-off-by: Sergei Trofimovich <slyich-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
---
 Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Makefile b/Makefile
index e7a0dcb..d4e7551 100644
--- a/Makefile
+++ b/Makefile
@@ -384,7 +384,7 @@ clean: libfdt_clean pylibfdt_clean tests_clean
 	@$(VECHO) LEX $@
 	$(LEX) -o$@ $<
 
-%.tab.c %.tab.h %.output: %.y
+%.tab.c %.tab.h: %.y
 	@$(VECHO) BISON $@
 	$(BISON) -b $(basename $(basename $@)) -d $<
 
-- 
2.37.2

Re: [PATCH 2/2] Makefile: fix infinite recursion by dropping non-existent `%.output`

[David Gibson]

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On Sun, Sep 25, 2022 at 11:42:03AM +0100, Sergei Trofimovich wrote:
> Without the change GNU `make-4.4` falls into infinite recursion of trying
> to generate %.output files (bison is not passed flags to generate debug
> output).
> 
> This happens on GNU `make-4.4` only after GNU make change to more eagerly
> rebuild all target outputs in multiple targets:
>     https://savannah.gnu.org/bugs/index.php?63098
> 
> The recursion here is the following:
> 
> - Makefile depends on *.d files
> - *.d files depend on *.c files
> - *.c files are generated by bison
> - bison is triggered whenever some of it's multiple targets are missing
> 
> In our case `%.output` is always missing and bison is always reran.
> *.d files are always regenerated on `make` run. And make is always
> restarted as *.d files are always regenerated.
> 
> The fix removes infeasible `%.output`.
> 
> Signed-off-by: Sergei Trofimovich <slyich-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>

Huh, interesting.  That .output target seems to have been there since
the dawn of time, really can't remember why it was included in the
first place.

Anyway, both patches applied, thanks.

> ---
>  Makefile | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/Makefile b/Makefile
> index e7a0dcb..d4e7551 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -384,7 +384,7 @@ clean: libfdt_clean pylibfdt_clean tests_clean
>  	@$(VECHO) LEX $@
>  	$(LEX) -o$@ $<
>  
> -%.tab.c %.tab.h %.output: %.y
> +%.tab.c %.tab.h: %.y
>  	@$(VECHO) BISON $@
>  	$(BISON) -b $(basename $(basename $@)) -d $<
>  

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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