Missing build dependency pesign on s390

Hi everybody, I was reported that 'dnf builddep kernel' fails on RHEL8 on s390 with No matching package to install: 'pesign >= 0.10-4' which doesn't make sense as the kernel.spec only adds pesign as build requirement for x86_64 and aarch64. While looking into this I think I fond a rather fundamental problem in the building process not only affecting RHEL8 but also RHEL7 and Fedora (guess CentOS too, but haven't checked). So I'm reaching out to you in the hope we can find a solution together. My theory is that the BuildRequires in the .spec file are only evaluated once during the creation of the srpm and then stored in a simple list in some rpm meta data in the header [1]. After that the meta data is fixed and any condition (architecture, with_* flags) are fixed to what was chosen while creating the srpm. Thus by sharing a srpm among the architectures all architectures get the same build requirements regardless of what's been defined for them in the kernel.spec. To proof the theory I took a closer look at a freshly downloaded the srpm (dnf download --source kernel) for RHEL8 on s390 and indeed its architecture (rpm -qi) is x86_64. After rebuilding the srpm (rpmbuild -rs) on s390 pesign is no longer listed as build requirement and dnf builddep works again. As said above RHEL7 and Fedora are also affected by the problem. The only reason why it does not show is that their srpms are build on ppc (3.10.0-1152.el7) and armv7hl (5.7.7-200.fc32), which both don't require pesign (which of course is missing for x86 in these cases...). Using the same trick from above, i.e. rebuilding the srpm on x86 and running dnf builddep on s390 triggers the same error as for RHEL8. To be honest I'm not really sure what I shall make of this problem myself. Currently it only seems to affect the build requirements, which is annoying but no real deal beaker. But it is easy to create cases where, e.g. Conflicts or even the License are affected, which elevates the problem to completely different levels. Sorry for the long mail Philipp P.S. Checking resent RHEL8 brew builds I see in the root.log that it too calls 'dnf builddep' on s390. Apparently without any problem. I have absolutely no clue what kind of magic is responsible for that. [1] http://ftp.rpm.org/max-rpm/s1-rpm-file-format-rpm-file-format.html#S2-RPM...