Re: [PATCH] kbuild: do not add srctree to sysroot relative includes

[Lars Persson]

On 08/16/2016 01:59 PM, Michal Marek wrote:
> On 2016-08-16 13:40, Lars Persson wrote:
> > We need to filter out also -I=/path to allow sysroot relative
> > include paths in the makefiles of external modules.
> >
> > Signed-off-by: Lars Persson <larper@xxxxxxxx>
> > ---
> >  scripts/Kbuild.include | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
> > index 1792198..ffe5c6c 100644
> > --- a/scripts/Kbuild.include
> > +++ b/scripts/Kbuild.include
> > @@ -206,7 +206,7 @@ hdr-inst := -f $(srctree)/scripts/Makefile.headersinst obj
> >  # Prefix -I with $(srctree) if it is not an absolute path.
> >  # skip if -I has no parameter
> >  addtree = $(if $(patsubst -I%,%,$(1)), \
> > -$(if $(filter-out -I/% -I./% -I../%,$(1)),$(patsubst -I%,-I$(srctree)/%,$(1)),$(1)))
> > +$(if $(filter-out -I/% -I./% -I../% -I=%,$(1)),$(patsubst -I%,-I$(srctree)/%,$(1)),$(1)))
>
> Hi Lars,
>
> Two questions: 1) Where is the -I=/... syntax documented? I could not
> find it gcc docs.

You should find this in your gcc manual:
If dir begins with "=", then the "=" will be replaced by the sysroot 
prefix; see --sysroot and -isysroot.


2) Why do these Makefiles use --sysroot at all? The
> kernel does not use any system libraries and the host programs are
> compiled for the host architecture.

One use-case is with the yocto build system. Suppose we have two kernel 
modules A and B. A installs header files into the sysroot that B will 
include.


- Lars