After the blamed commit, running a out-of-tree build for ynltool fails :

  # make -C tools/net/ynl/ynltool O=/tmp/o1
  make: Entering directory 'tools/net/ynl/ynltool'
  make: *** No rule to make target '/tmp/o1/json_writer.o', needed by '/tmp/o1/ynltool'.  Stop.

ynltool's Makefile correctly accounts for $(OUTPUT) to get the list of
object files to generate :

OBJS := $(patsubst %.c,$(OUTPUT)%.o,$(SRCS))

but it never actually set $(OUTPUT) before the blamed commit, meaning
that out-of-tree buils of ynltool were always actually in-tree.

Now, the O= parameter is correctly accounted for, and the %o: %c rule fails.

Let's update the %o: %c rule to also use $(OUTPUT).

Reported-by: Bobby Eshleman <bobbyeshleman@gmail.com>
Closes: https://lore.kernel.org/all/aqCyWQxqKDuQnZYR@devvm29614.prn0.facebook.com/
Fixes: 917f713b4ec4 ("tools: ynl: Allow cross-compiling ynl and associated tools")
Signed-off-by: Maxime Chevallier (Netdev Foundation) <maxime.chevallier@bootlin.com>
---
Re-sending, the previous submission didn't reach netdev@ :/
Fixes a bug in net-next, so targetting net-next.

 tools/net/ynl/ynltool/Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/net/ynl/ynltool/Makefile b/tools/net/ynl/ynltool/Makefile
index b8c67cdb4fdf..1053e7606c86 100644
--- a/tools/net/ynl/ynltool/Makefile
+++ b/tools/net/ynl/ynltool/Makefile
@@ -31,7 +31,7 @@ $(YNLTOOL): ../libynl.a $(OBJS)
 	$(Q)echo -e "\tLINK $@"
 	$(Q)$(CC) $(CFLAGS) -o $@ $(OBJS) ../libynl.a -lm
 
-%.o: %.c ../libynl.a
+$(OUTPUT)%.o: %.c ../libynl.a
 	$(Q)echo -e "\tCC $@"
 	$(Q)$(COMPILE.c) -MMD -c -o $@ $<
 
-- 
2.55.0

Thank you for your contribution! Sashiko AI review found 2 potential
issue(s) to consider:

Critical: 0 · High: 0 · Medium: 2 · Low: 0

- [Medium] Incomplete $(OUTPUT) plumbing in
  tools/net/ynl/ynltool/Makefile: the patched rule `$(OUTPUT)%.o: %.c`…
- [Medium] The `install` target in tools/net/ynl/ynltool/Makefile (lines
  49-50) reuses `$(YNLTOOL)` as the destination file name: `$(INSTALL)…

--

tools: ynl: Fix out-of-tree build for ynltool

This changes the object compile rule in tools/net/ynl/ynltool/Makefile from
%.o: %.c to $(OUTPUT)%.o: %.c so that the pattern rule matches the
$(OUTPUT)-prefixed object names already used in OBJS.  This unblocks
make -C tools/net/ynl/ynltool O=<dir>, which previously stopped with
"No rule to make target '/tmp/o1/json_writer.o'".

Closes: https://lore.kernel.org/all/aqCyWQxqKDuQnZYR@devvm29614.prn0.facebook.com/

> diff --git a/tools/net/ynl/ynltool/Makefile b/tools/net/ynl/ynltool/Makefile
> index b8c67cdb4fdf0..1053e7606c86c 100644
> --- a/tools/net/ynl/ynltool/Makefile
> +++ b/tools/net/ynl/ynltool/Makefile
> @@ -31,7 +31,7 @@ $(YNLTOOL): ../libynl.a $(OBJS)
>  	$(Q)echo -e "\tLINK $@"
>  	$(Q)$(CC) $(CFLAGS) -o $@ $(OBJS) ../libynl.a -lm
>  
> -%.o: %.c ../libynl.a
> +$(OUTPUT)%.o: %.c ../libynl.a
>  	$(Q)echo -e "\tCC $@"
>  	$(Q)$(COMPILE.c) -MMD -c -o $@ $<

[Severity: Medium]
Since -MMD derives the depfile name from the -o argument, does this rule
now write the dependency files into $(OUTPUT) as well, i.e. /tmp/o1/foo.d
next to /tmp/o1/foo.o?

The consumer side of that convention still globs the source directory only:

tools/net/ynl/ynltool/Makefile:
	include $(wildcard *.d)

With OUTPUT set to an absolute path ending in '/' (tools/scripts/Makefile.include
defines OUTPUT := $(ABSOLUTE_O)/$(if $(subdir),$(subdir)/) when O= is given
on the command line), can *.d ever match /tmp/o1/*.d?  If it cannot, are
header dependencies simply untracked for the O= builds this patch enables?

The only remaining prerequisites of $(OUTPUT)%.o are the .c file and
../libynl.a, and that archive has no prerequisites of its own:

tools/net/ynl/ynltool/Makefile:
	../libynl.a:
		$(Q)$(MAKE) -C ../

so once ../libynl.a exists make treats it as up to date.  Does editing a
header under ../lib, or regenerating ../generated, then leave a stale
$(OUTPUT)foo.o to be re-linked into $(OUTPUT)ynltool?

Related, the clean recipe only touches the source directory:

tools/net/ynl/ynltool/Makefile:
	clean:
		rm -f *.o *.d *~

Is make O=/tmp/o1 clean a no-op for the artifacts the new rule produces,
leaving no way to force the rebuild?  Note distclean just below it is
$(OUTPUT)-aware through $(YNLTOOL).  Would it make sense to change the
include to $(wildcard $(OUTPUT)*.d) and the clean recipe to remove
$(OUTPUT)*.o and $(OUTPUT)*.d in the same patch?

[Severity: Medium]
The commit message says "Now, the O= parameter is correctly accounted for",
but there is another $(OUTPUT) consumer left in this same Makefile:

tools/net/ynl/ynltool/Makefile:
	YNLTOOL := $(OUTPUT)ynltool
	...
	bindir ?= /usr/bin

	install: $(YNLTOOL)
		$(INSTALL) -m 0755 $(YNLTOOL) $(DESTDIR)$(bindir)/$(YNLTOOL)

Since $(YNLTOOL) carries the absolute $(OUTPUT) prefix, does
make -C tools/net/ynl/ynltool O=/tmp/o1 install expand to

	install -m 0755 /tmp/o1/ynltool /usr/bin//tmp/o1/ynltool

and fail with ENOENT because the intermediate directories do not exist?
With a non-empty DESTDIR that happens to contain that nested path, would
the binary instead land somewhere unintended?

Should the destination be $(DESTDIR)$(bindir)/ynltool, or
$(DESTDIR)$(bindir)/$(notdir $(YNLTOOL))?

The same path is reachable from the parent Makefile, which recurses with

tools/net/ynl/Makefile:
	@make -C ynltool install

and a command-line O= is inherited through MAKEFLAGS, so does
make -C tools/net/ynl O=<dir> install fail the same way?

Unrelated to O=, bindir ?= /usr/bin hardcodes the path while the
prefix ?= /usr declared earlier in the same file is never used, whereas the
parent Makefile derives libdir and includedir from $(prefix).  Was the
inconsistency intended?

-- 
Sashiko AI review · https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20260910165451.1027541-1-maxime.chevallier%40bootlin.com

Hi Maxime

On 10.9.2026 18:54, Maxime Chevallier (Netdev Foundation) wrote:
> After the blamed commit, running a out-of-tree build for ynltool fails 
> :
> 
>   # make -C tools/net/ynl/ynltool O=/tmp/o1
>   make: Entering directory 'tools/net/ynl/ynltool'
>   make: *** No rule to make target '/tmp/o1/json_writer.o', needed by 
> '/tmp/o1/ynltool'.  Stop.
> 
> ynltool's Makefile correctly accounts for $(OUTPUT) to get the list of
> object files to generate :
> 
> OBJS := $(patsubst %.c,$(OUTPUT)%.o,$(SRCS))
> 
> but it never actually set $(OUTPUT) before the blamed commit, meaning
> that out-of-tree buils of ynltool were always actually in-tree.
> 
> Now, the O= parameter is correctly accounted for, and the %o: %c rule 
> fails.
> 
> Let's update the %o: %c rule to also use $(OUTPUT).
> 
> Reported-by: Bobby Eshleman <bobbyeshleman@gmail.com>
> Closes: 
> https://lore.kernel.org/all/aqCyWQxqKDuQnZYR@devvm29614.prn0.facebook.com/
> Fixes: 917f713b4ec4 ("tools: ynl: Allow cross-compiling ynl and 
> associated tools")
> Signed-off-by: Maxime Chevallier (Netdev Foundation) 
> <maxime.chevallier@bootlin.com>
> ---
> Re-sending, the previous submission didn't reach netdev@ :/
> Fixes a bug in net-next, so targetting net-next.
> 
>  tools/net/ynl/ynltool/Makefile | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/net/ynl/ynltool/Makefile 
> b/tools/net/ynl/ynltool/Makefile
> index b8c67cdb4fdf..1053e7606c86 100644
> --- a/tools/net/ynl/ynltool/Makefile
> +++ b/tools/net/ynl/ynltool/Makefile
> @@ -31,7 +31,7 @@ $(YNLTOOL): ../libynl.a $(OBJS)
>  	$(Q)echo -e "\tLINK $@"
>  	$(Q)$(CC) $(CFLAGS) -o $@ $(OBJS) ../libynl.a -lm
> 
> -%.o: %.c ../libynl.a
> +$(OUTPUT)%.o: %.c ../libynl.a

There is a second issue if I'm not mistaken:

   out=$(mktemp -d)
   make -C tools/net/ynl/ynltool O="$out"
   touch tools/net/ynl/ynltool/main.h
   make -C tools/net/ynl/ynltool O="$out"

-> make: Nothing to be done for 'all'.

Add $(OUTPUT) to the wildcard include

   include $(wildcard $(OUTPUT)*.d)

and it works.

>  	$(Q)echo -e "\tCC $@"
>  	$(Q)$(COMPILE.c) -MMD -c -o $@ $<

Thanks,
Nicolai