linux-kernel - Re: [PATCH regression 4.0 -> 4.1] tools perf: Fix build breakage if prefix= is specified

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Date:	Thu, 18 Jun 2015 21:59:55 +0200
From:	Lukas Wunner <lukas@...ner.de>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH regression 4.0 -> 4.1] tools perf: Fix build breakage if
 prefix= is specified

Hi Jirka,

On Thu, Jun 18, 2015 at 09:29:32PM +0200, Jiri Olsa wrote:
> On Thu, Jun 18, 2015 at 01:00:32PM +0200, Lukas Wunner wrote:
> > Invoking Makefile.perf with prefix= breaks the build since Makefile.perf
> > hands that variable down to Makefile.build where it overrides
> >     prefix       := $(subst ./,,$(OUTPUT)$(dir)/)
> > 
> > leading to errors like this:
> >     No rule to make target '/usrabspath.o', needed by '/usrlibperf-in.o'
> hum, what specific make command is failing?

Makefile.perf may be invoked with a "prefix" parameter:

	@echo '  HINT: use "prefix" or "DESTDIR" to install to a particular'
	@echo '        path like "make prefix=/usr/local install install-doc"'

Source: https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git/tree/tools/perf/Makefile.perf#n414


E.g. the Debian "linux-tools" package makes use of that feature:

	MAKE_PERF := $(MAKE) prefix=/usr V=1 ARCH=$(KERNEL_ARCH_PERF) EXTRA_WARNINGS=-Wno-error

Source: http://anonscm.debian.org/viewvc/kernel/dists/trunk/linux-tools/debian/build/tools/perf/Makefile?view=markup (line 29)


The "prefix" parameter is handed down from Makefile.perf to Makefile.build
because it's invoked with $(MAKE), so the command line parameters are
inherited to Makefile.build:

	$(Q)$(MAKE) $(build)=perf

Source: https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git/tree/tools/perf/Makefile.perf#n282


That "prefix" feature is broken in all 4.1 release candidates because a
variable definition specified on the make command line is an "overriding
variable", so this definition in line 97 of tools/build/Makefile.build
has no effect:

	prefix       := $(subst ./,,$(OUTPUT)$(dir)/)

Source: https://www.gnu.org/software/make/manual/html_node/Overriding.html


So $(prefix) contains the wrong value, yet is subsequently used in
Makefile.build, causing the build to break.


Best regards,

Lukas

> 
> jirka
> 
> > 
> > Fixes: c819e2cf2eb6f65d3208d195d7a0edef6108d5
> > Signed-off-by: Lukas Wunner <lukas@...ner.de>
> > ---
> >  tools/build/Makefile.build | 8 ++++----
> >  1 file changed, 4 insertions(+), 4 deletions(-)
> > 
> > diff --git a/tools/build/Makefile.build b/tools/build/Makefile.build
> > index 10df572..98cfc38 100644
> > --- a/tools/build/Makefile.build
> > +++ b/tools/build/Makefile.build
> > @@ -94,12 +94,12 @@ obj-y        := $(patsubst %/, %/$(obj)-in.o, $(obj-y))
> >  subdir-obj-y := $(filter %/$(obj)-in.o, $(obj-y))
> >  
> >  # '$(OUTPUT)/dir' prefix to all objects
> > -prefix       := $(subst ./,,$(OUTPUT)$(dir)/)
> > -obj-y        := $(addprefix $(prefix),$(obj-y))
> > -subdir-obj-y := $(addprefix $(prefix),$(subdir-obj-y))
> > +objprefix    := $(subst ./,,$(OUTPUT)$(dir)/)
> > +obj-y        := $(addprefix $(objprefix),$(obj-y))
> > +subdir-obj-y := $(addprefix $(objprefix),$(subdir-obj-y))
> >  
> >  # Final '$(obj)-in.o' object
> > -in-target := $(prefix)$(obj)-in.o
> > +in-target := $(objprefix)$(obj)-in.o
> >  
> >  PHONY += $(subdir-y)
> >  
> > -- 
> > 1.8.5.2 (Apple Git-48)
> > 
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