Re: [PATCH v9 1/4] Create source symlink in perf object dir

[Luca Ceresoli <luca.ceresoli@bootlin.com>]

Hello Andi,

thanks for the feedback.

On Mon, 25 Nov 2024 11:12:50 -0800
Andi Kleen <ak@linux.intel.com> wrote:

> On Mon, Nov 25, 2024 at 06:25:06PM +0100, Luca Ceresoli wrote:
> > Hello Andi,
> > 
> > +cc Yann and the Buildroot mailing list (see the end of this report).
> > 
> > On Wed,  7 Aug 2024 16:18:20 -0700
> > Andi Kleen <ak@linux.intel.com> wrote:
> >   
> > > Create a source symlink to the original source in the objdir.
> > > This is similar to what the main kernel build script does.
> > > 
> > > Signed-off-by: Andi Kleen <ak@linux.intel.com>
> > > ---
> > >  tools/perf/Makefile.perf | 2 ++
> > >  1 file changed, 2 insertions(+)
> > > 
> > > diff --git a/tools/perf/Makefile.perf b/tools/perf/Makefile.perf
> > > index 175e4c7898f0..d46892d8223b 100644
> > > --- a/tools/perf/Makefile.perf
> > > +++ b/tools/perf/Makefile.perf
> > > @@ -163,6 +163,8 @@ ifneq ($(OUTPUT),)
> > >  # for flex/bison parsers.
> > >  VPATH += $(OUTPUT)
> > >  export VPATH
> > > +# create symlink to the original source
> > > +SOURCE := $(shell ln -sf $(srctree)/tools/perf $(OUTPUT)/source)  
> > 
> > I found that since this patch got applied in 890a1961c812 (v6.12-rc1)
> > building perf fails silently in some cases.
> > 
> > The cases I have tested:
> >  - make <FLAGS> -C tools/perf                       -> OK
> >  - make <FLAGS> -C tools/perf O=/my/out/of/tree/dir -> OK
> >  - make <FLAGS> -C tools/perf O=tools/perf          -> fails
> > 
> > The failure in the third case is silent: make exits with a return value
> > of 0, but there is no perf executable created.  
> 
> The failing case is incorrect arguments because the O= is relative to -C 
> and there is no tools/perf/tools/perf

OK. However I get the same result even with O=$(pwd)/tools/perf, which
is precisely what Buildroot does:
https://git.buildroot.net/buildroot/tree/package/linux-tools/linux-tool-perf.mk.in#n170

> But yes a error message would be good.

Sure, as well as a non-zero return value.

> Could just ignore the linking error, so that you hopefully get a better
> error message later.
> 
> diff --git a/tools/perf/Makefile.perf b/tools/perf/Makefile.perf
> index 9dd2e8d3f3c9..18f639ec853b 100644
> --- a/tools/perf/Makefile.perf
> +++ b/tools/perf/Makefile.perf
> @@ -164,7 +164,7 @@ ifneq ($(OUTPUT),)
>  VPATH += $(OUTPUT)
>  export VPATH
>  # create symlink to the original source
> -SOURCE := $(shell ln -sf $(srctree)/tools/perf $(OUTPUT)/source)
> +SOURCE := $(shell ln -sf $(srctree)/tools/perf $(OUTPUT)/source || true)

I tried this but I don't see any difference. What is the change you
would have expected in the build output?

I'm afraid I don't understand what the SOURCE variable is supposed to
do so I can hardly follow the logic.

Luca

-- 
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com