This fixes cross-building in some scenarios. Specifically, when building for armv7l on x86_64, has_header() will see the x86_64 version of the header and consider it usable. Later, when an attempt is made to actually use it, the compiler will quickly realize that things can't quite work. The reason why we haven't hit this in our CI is that we only ever install the foreign version of header files. When building the Debian package, however, some of the Debian-specific tooling will bring in the native version of the Linux headers in addition to the foreign one, causing Meson to misreport the header's availability status. Checking for its actual usability, as opposed to mere presence, is enough to make things work correctly in all cases. https://bugs.debian.org/1024504 Suggested-by: Helmut Grohne <helmut(a)subdivi.de&gt; Signed-off-by: Andrea Bolognani <abologna(a)redhat.com&gt; --- meson.build | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) diff --git a/meson.build b/meson.build index d35d5e076b..21a4bd5b37 100644 --- a/meson.build +++ b/meson.build @@ -614,7 +614,6 @@ headers = [ 'asm/hwcap.h', 'ifaddrs.h', 'libtasn1.h', - 'linux/kvm.h', 'mntent.h', 'net/ethernet.h', 'net/if.h', @@ -635,12 +634,24 @@ if host_machine.system() == 'freebsd' headers += 'libutil.h' endif +# headers for which we need to check actual usability. in most +# cases, checking for presence is enough (and it's way faster) +check_headers = [ + 'linux/kvm.h', +] + foreach name : headers if cc.has_header(name) conf.set(&#39;WITH_@0(a)&#39;.format(name.underscorify().to_upper()), 1) endif endforeach +foreach name : check_headers + if cc.check_header(name) + conf.set(&#39;WITH_@0(a)&#39;.format(name.underscorify().to_upper()), 1) + endif +endforeach + # check for kernel header required by src/util/virnetdevbridge.c if host_machine.system() == 'linux' if not cc.has_header('linux/sockios.h')

On Thu, Apr 27, 2023 at 11:50:05AM +0200, Michal Prívozník wrote: > On 4/27/23 11:41, Andrea Bolognani wrote: > > +# headers for which we need to check actual usability. in most > > +# cases, checking for presence is enough (and it's way faster) > > +check_headers = [ > > + 'linux/kvm.h', > > +] > > + > > +foreach name : check_headers > > + if cc.check_header(name) > > + conf.set(&#39;WITH_@0(a)&#39;.format(name.underscorify().to_upper()), 1) > > + endif > > +endforeach > > One could argue, that the semantics of has_header() is broken then. What > good is there to check if the host has a header file when compiler > rejects it subsequently? > > But leaving meson aside, shouldn't we just use check_header() for every > header file then? I mean, this fixes this particular instance of the > problem, but can't we hit it again with say ifaddrs.h or any other > header file on the list? We could. The Meson documentation recommends not doing this, as check_header() is (understandably) slower than has_header(). I haven't tried to see how much slower we're actually talking... Maybe for the 20-ish headers that we care about, it wouldn't make a measurable difference? Especially since the results of the check are cached between Meson runs.