Re: [igt-dev] [PATCH i-g-t 1/4] tests: add libatomic dependency

["Ser, Simon" <simon.ser@intel.com>]

On Thu, 2019-06-13 at 13:55 +0100, Guillaume Tucker wrote:
> On 06/06/2019 08:18, Ser, Simon wrote:
> > On Mon, 2019-06-03 at 12:54 +0100, Guillaume Tucker wrote:
> > > Add dependency to libatomic in order to be able to use the __atomic_*
> > > functions instead of the older __sync_* ones.  This is to enable
> > > atomic operations on a wider number of architectures including MIPS.
> > 
> > Thanks for your patch! I have a few questions because I don't know well
> > how libatomic works.
> 
> Thanks for the review!
> 
> > Do we want to always link against libatomic? For instance LLVM tries to
> > compile a program with atomic before falling back to libatomic:
> > https://github.com/llvm-mirror/llvm/blob/master/cmake/modules/CheckAtomic.cmake
> > 
> > Should this dependency be mandatory?
> 
> I've had a look around, the short answer is we should make this
> dependency optional.  I'm sending a v2 of this series which
> addresses this issue.
> 
> From what I understand, linking against libatomic is actually
> only needed when some atomic operations aren't supported natively
> by a CPU architecture.  For example, this is the case with 64-bit
> atomics on 32-bit MIPS.  If the CPU can't do an atomic operation
> and there's no libatomic available, then it won't build.  So I've
> made a test in meson.build to check whether linking against
> libatomic is required or not, to drop the dependency when it
> isn't.  I've verified that the test passes on x86 (i.e. no
> dependency) and fails on 32-bit MIPS (i.e. with dependency).

Nice! Looks like a good idea to me.

> Guillaume
> 
> 
> > > Signed-off-by: Guillaume Tucker <guillaume.tucker@collabora.com>
> > > ---
> > >  meson.build       | 1 +
> > >  tests/meson.build | 2 +-
> > >  2 files changed, 2 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/meson.build b/meson.build
> > > index 6268c58d3634..4e5bb323fa49 100644
> > > --- a/meson.build
> > > +++ b/meson.build
> > > @@ -179,6 +179,7 @@ math = cc.find_library('m')
> > >  realtime = cc.find_library('rt')
> > >  dlsym = cc.find_library('dl')
> > >  zlib = cc.find_library('z')
> > > +libatomic = cc.find_library('atomic')
> > >  
> > >  if cc.has_header('linux/kd.h')
> > >  	config.set('HAVE_LINUX_KD_H', 1)
> > > diff --git a/tests/meson.build b/tests/meson.build
> > > index 806766e51667..6877ccd59235 100644
> > > --- a/tests/meson.build
> > > +++ b/tests/meson.build
> > > @@ -233,7 +233,7 @@ i915_progs = [
> > >  	'i915_suspend',
> > >  ]
> > >  
> > > -test_deps = [ igt_deps ]
> > > +test_deps = [ igt_deps, libatomic ]
> > >  
> > >  if libdrm_nouveau.found()
> > >  	test_progs += [
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