[PATCH] dtc: Use pkg-config to locate libyaml

[PATCH] dtc: Use pkg-config to locate libyaml

[Pavel Modilaynen]

From: Pavel Modilaynen <pavel.modilaynen@axis.com>

Using Makefile's wildcard with absolute path to detect
the presence of libyaml results in false-positive
detection when cross-compiling e.g. in yocto environment.
The latter results in build error:
| scripts/dtc/yamltree.o: In function `yaml_propval_int':
| yamltree.c: undefined reference to `yaml_sequence_start_event_initialize'
| yamltree.c: undefined reference to `yaml_emitter_emit'
| yamltree.c: undefined reference to `yaml_scalar_event_initialize'
...
Use pkg-config to locate libyaml to address this scenario.

Signed-off-by: Pavel Modilaynen <pavel.modilaynen@axis.com>
---
 scripts/dtc/Makefile | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/scripts/dtc/Makefile b/scripts/dtc/Makefile
index 82160808765c..99d51b665432 100644
--- a/scripts/dtc/Makefile
+++ b/scripts/dtc/Makefile
@@ -11,7 +11,7 @@ dtc-objs	+= dtc-lexer.lex.o dtc-parser.tab.o
 # Source files need to get at the userspace version of libfdt_env.h to compile
 HOST_EXTRACFLAGS := -I $(srctree)/$(src)/libfdt
 
-ifeq ($(wildcard /usr/include/yaml.h),)
+ifeq ($(shell pkg-config --exists yaml-0.1 && echo yes),)
 ifneq ($(CHECK_DTBS),)
 $(error dtc needs libyaml for DT schema validation support. \
 	Install the necessary libyaml development package.)
@@ -19,7 +19,7 @@ endif
 HOST_EXTRACFLAGS += -DNO_YAML
 else
 dtc-objs	+= yamltree.o
-HOSTLDLIBS_dtc	:= -lyaml
+HOSTLDLIBS_dtc	:= $(shell pkg-config yaml-0.1 --libs)
 endif
 
 # Generated files need one more search path to include headers in source tree
-- 
2.11.0

Re: [PATCH] dtc: Use pkg-config to locate libyaml

[Rob Herring]

+Masahiro

On Fri, Jul 12, 2019 at 6:59 AM Pavel Modilaynen
<pavel.modilaynen@axis.com> wrote:
>
> From: Pavel Modilaynen <pavel.modilaynen@axis.com>

Sorry for missing this.

> Using Makefile's wildcard with absolute path to detect
> the presence of libyaml results in false-positive
> detection when cross-compiling e.g. in yocto environment.

As this is a host tool, it's not really about cross-compiling, but
sandboxing the host env? IOW, I cross-compile all the time and don't
have an issue.

> The latter results in build error:
> | scripts/dtc/yamltree.o: In function `yaml_propval_int':
> | yamltree.c: undefined reference to `yaml_sequence_start_event_initialize'
> | yamltree.c: undefined reference to `yaml_emitter_emit'
> | yamltree.c: undefined reference to `yaml_scalar_event_initialize'
> ...
> Use pkg-config to locate libyaml to address this scenario.

The reason I didn't use pkg-config in the first place is it adds
another dependency. AIUI, it's only needed for gconfig/xconfig which
are probably not widely used especially for CI. Looks like objtool
needs it too, but that's x86 only though arm64 support is being worked
on. So I guess it is pretty much becoming a requirement.

So I've applied it. I added suppressing stderr in case pkg-config
isn't present.

Rob

>
> Signed-off-by: Pavel Modilaynen <pavel.modilaynen@axis.com>
> ---
>  scripts/dtc/Makefile | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/scripts/dtc/Makefile b/scripts/dtc/Makefile
> index 82160808765c..99d51b665432 100644
> --- a/scripts/dtc/Makefile
> +++ b/scripts/dtc/Makefile
> @@ -11,7 +11,7 @@ dtc-objs      += dtc-lexer.lex.o dtc-parser.tab.o
>  # Source files need to get at the userspace version of libfdt_env.h to compile
>  HOST_EXTRACFLAGS := -I $(srctree)/$(src)/libfdt
>
> -ifeq ($(wildcard /usr/include/yaml.h),)
> +ifeq ($(shell pkg-config --exists yaml-0.1 && echo yes),)
>  ifneq ($(CHECK_DTBS),)
>  $(error dtc needs libyaml for DT schema validation support. \
>         Install the necessary libyaml development package.)
> @@ -19,7 +19,7 @@ endif
>  HOST_EXTRACFLAGS += -DNO_YAML
>  else
>  dtc-objs       += yamltree.o
> -HOSTLDLIBS_dtc := -lyaml
> +HOSTLDLIBS_dtc := $(shell pkg-config yaml-0.1 --libs)
>  endif
>
>  # Generated files need one more search path to include headers in source tree
> --
> 2.11.0
>

RE: [PATCH] dtc: Use pkg-config to locate libyaml

[Pavel Modilaynen]

> From: Rob Herring <robh+dt@kernel.org>

> > Using Makefile's wildcard with absolute path to detect the presence of
> > libyaml results in false-positive detection when cross-compiling e.g.
> > in yocto environment.
> 
> As this is a host tool, it's not really about cross-compiling, but sandboxing the
> host env? IOW, I cross-compile all the time and don't have an issue.

Yes, you are correct, this is to address sandboxing, too late to correct?

> 
> > Use pkg-config to locate libyaml to address this scenario.
> 
> The reason I didn't use pkg-config in the first place is it adds another
> dependency. AIUI, it's only needed for gconfig/xconfig which are probably
> not widely used especially for CI. Looks like objtool needs it too, but that's
> x86 only though arm64 support is being worked on. So I guess it is pretty
> much becoming a requirement.

Exactly, the patch was inspired by usage of pkg-config in that shell scripts 
assuming that it's more correct way to handle libyaml dependency...
I see it also used for building tools.

Should I maybe add new patch to fallback to wildcard when pkg-config is not found?

> 
> So I've applied it. I added suppressing stderr in case pkg-config isn't present.

Thank you!

Pavel