Date: Thu, 27 Jun 2024 17:22:31 +0200
From: Guilherme Amadio <amadio@...too.org>
To: Arnaldo Carvalho de Melo <acme@...nel.org>
Cc: Namhyung Kim <namhyung@...nel.org>, Ian Rogers <irogers@...gle.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-perf-users@...gentoo.org
Subject: Re: [PATCH 1/2] perf build: Use pkg-config for feature check for
 libtrace{event,fs}

Hi Arnaldo,

On Wed, Jun 26, 2024 at 04:19:57PM -0300, Arnaldo Carvalho de Melo wrote:
> Sorry, forgot to CC the mailing lists.
>
> On Wed, Jun 26, 2024 at 04:19:29PM -0300, Arnaldo Carvalho de Melo wrote:
> > On Tue, Jun 25, 2024 at 09:36:35PM +0200, Guilherme Amadio wrote:
> > > On Mon, Jun 24, 2024 at 10:50:56AM -0700, Namhyung Kim wrote:
> > > > On Thu, 06 Jun 2024 17:33:01 +0200, amadio@...too.org wrote:
> > > >
> > > > > Needed to add required include directories for the feature detection
> > > > > to succeed. The header tracefs.h is installed either into the include
> > > > > directory /usr/include/tracefs/tracefs.h when using the Makefile, or
> > > > > into /usr/include/libtracefs/tracefs.h when using meson to build
> > > > > libtracefs. The header tracefs.h uses #include <event-parse.h> from
> > > > > libtraceevent, so pkg-config needs to pick the correct include directory
> > > > > for libtracefs and add the one for libtraceevent to succeed.
> > > > >
> > > > > [...]
> > > >
> > > > Applied both to perf-tools-next, thanks!
> > >
> > > Thank you very much!
> >
> > So now when we don't libtracefs installed we get (with current
> > perf-tools-next):
> >
> > ⬢[acme@...lbox perf-tools-next]$ m
> > make: Entering directory '/home/acme/git/perf-tools-next/tools/perf'
> >   BUILD:   Doing 'make -j28' parallel build
> >   HOSTCC  /tmp/build/perf-tools-next/fixdep.o
> >   HOSTLD  /tmp/build/perf-tools-next/fixdep-in.o
> >   LINK    /tmp/build/perf-tools-next/fixdep
> > Warning: Kernel ABI header differences:
> >   diff -u tools/include/uapi/drm/i915_drm.h include/uapi/drm/i915_drm.h
> >   diff -u tools/include/uapi/linux/kvm.h include/uapi/linux/kvm.h
> >   diff -u tools/include/uapi/linux/stat.h include/uapi/linux/stat.h
> >   diff -u tools/arch/x86/include/asm/msr-index.h arch/x86/include/asm/msr-index.h
> >   diff -u tools/arch/x86/include/uapi/asm/kvm.h arch/x86/include/uapi/asm/kvm.h
> >   diff -u tools/include/uapi/asm-generic/unistd.h include/uapi/asm-generic/unistd.h
> >   diff -u tools/arch/arm64/include/asm/cputype.h arch/arm64/include/asm/cputype.h
> >   diff -u tools/perf/arch/x86/entry/syscalls/syscall_64.tbl arch/x86/entry/syscalls/syscall_64.tbl
> >   diff -u tools/perf/arch/powerpc/entry/syscalls/syscall.tbl arch/powerpc/kernel/syscalls/syscall.tbl
> >   diff -u tools/perf/arch/s390/entry/syscalls/syscall.tbl arch/s390/kernel/syscalls/syscall.tbl
> >   diff -u tools/perf/arch/mips/entry/syscalls/syscall_n64.tbl arch/mips/kernel/syscalls/syscall_n64.tbl
> >   diff -u tools/perf/trace/beauty/arch/x86/include/asm/irq_vectors.h arch/x86/include/asm/irq_vectors.h
> >   diff -u tools/perf/trace/beauty/include/linux/socket.h include/linux/socket.h
> >   diff -u tools/perf/trace/beauty/include/uapi/linux/fcntl.h include/uapi/linux/fcntl.h
> >   diff -u tools/perf/trace/beauty/include/uapi/linux/prctl.h include/uapi/linux/prctl.h
> >   diff -u tools/perf/trace/beauty/include/uapi/linux/stat.h include/uapi/linux/stat.h
> > Package libtracefs was not found in the pkg-config search path.
> > Perhaps you should add the directory containing `libtracefs.pc'
> > to the PKG_CONFIG_PATH environment variable
> > Package 'libtracefs', required by 'virtual:world', not found
> > Package libtracefs was not found in the pkg-config search path.
> > Perhaps you should add the directory containing `libtracefs.pc'
> > to the PKG_CONFIG_PATH environment variable
> > Package 'libtracefs', required by 'virtual:world', not found
> >
> > Auto-detecting system features:
> > ...                                   dwarf: [ on  ]
> > ...                      dwarf_getlocations: [ on  ]
> > ...                                   glibc: [ on  ]
> > ...                                  libbfd: [ on  ]
> > ...                          libbfd-buildid: [ on  ]
> > ...                                  libcap: [ on  ]
> > ...                                  libelf: [ on  ]
> > ...                                 libnuma: [ on  ]
> > ...                  numa_num_possible_cpus: [ on  ]
> > ...                                 libperl: [ on  ]
> > ...                               libpython: [ on  ]
> > ...                               libcrypto: [ on  ]
> > ...                               libunwind: [ on  ]
> > ...                      libdw-dwarf-unwind: [ on  ]
> > ...                             libcapstone: [ on  ]
> > ...                                    zlib: [ on  ]
> > ...                                    lzma: [ on  ]
> > ...                               get_cpuid: [ on  ]
> > ...                                     bpf: [ on  ]
> > ...                                  libaio: [ on  ]
> > ...                                 libzstd: [ on  ]
> >
> >   GEN     /tmp/build/perf-tools-next/common-cmds.h
> >   GEN     /tmp/build/perf-tools-next/arch/arm64/include/generated/asm/sysreg-defs.h
> >
> > Which is a new behaviour, we never had those kinds of warnings from
> > pkg-config, and when something wasn´t available we would reflect that
> > somehow in the "Auto-detecting system features", additionally telling
> > the users which set of features would not be available due to some
> > system component not being available.
> >
> > Further more we would suggest the name of the package to install.
> >
> > Now I have this "virtual:world" thing that I never heard about (what is
> > that)?

We are calling, e.g. pkg-config --libs libtraceevent, but the package is
not there. I changed the Makefile to only add these calls for the
feature check if the package is actually installed, by calling first
pkg-config --exists libtraceevent.

> > Ditto for PKG_CONFIG_PATH, I probably guess what this is about, but then
> > it is a novelty for people with just enough muscle memory to build the
> > kernel, build perf and use it.
> >
> > If I try:
> >
> > $ sudo dnf install libtracefs
> >
> > Cool:
> >
> > Installed:
> >   libtracefs-1.6.4-3.fc39.x86_64
> >
> > Complete!
> > $
> >
> > but then when I try to build perf again I get those warnings again, but
> > a full build neverthless:
> >
> > Package libtracefs was not found in the pkg-config search path.
> > Perhaps you should add the directory containing `libtracefs.pc'
> > to the PKG_CONFIG_PATH environment variable
> > Package 'libtracefs', required by 'virtual:world', not found
> > Package libtracefs was not found in the pkg-config search path.
> > Perhaps you should add the directory containing `libtracefs.pc'
> > to the PKG_CONFIG_PATH environment variable
> > Package 'libtracefs', required by 'virtual:world', not found
> >
> > Its only when I try:
> >
> > $ sudo dnf install libtracefs-devel
> >
> > That I get a build without warnings.
> >
> > So, what is the feature detection that is failing when libtracefs-devel
> > isn't installed? What are the features that we lose in such a situation?

I added a warning for when libtraceevent-devel is installed, but not
libtracefs-devel. So if someone forgets to install the latter, there
will be a message to remind them now.

Indeed, this was not very nice behavior which was introduced. I've sent
the patches to address this to the list. I tried to set the reply-to to
this message, but it doesn't seem to have worked, unfortunately. Please
let me know if the new patches are ok or if you have any suggestions for
improvement.

Best regards,
-Guilherme

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