On Tue, Jun 18, 2019 at 02:55:12PM +0200, Peter Zijlstra wrote: > On Tue, Jun 18, 2019 at 02:47:00PM +0200, Florian Weimer wrote: > > * Peter Zijlstra: > > > > > I'm not sure I read Thomas' comment like that. In my reading keeping the > > > PT_NOTE fallback is exactly one of those 'fly workarounds'. By not > > > supporting PT_NOTE only the 'fine' people already shit^Hpping this out > > > of tree are affected, and we don't have to care about them at all. > > > > Just to be clear here: There was an ABI document that required PT_NOTE > > parsing. > > URGH. > > > The Linux kernel does *not* define the x86-64 ABI, it only > > implements it. The authoritative source should be the ABI document. > > > > In this particularly case, so far anyone implementing this ABI extension > > tried to provide value by changing it, sometimes successfully. Which > > makes me wonder why we even bother to mainatain ABI documentation. The > > kernel is just very late to the party. > > How can the kernel be late to the party if all of this is spinning > wheels without kernel support? PT_GNU_PROPERTY is mentioned and allocated a p_type value in hjl's spec [1], but otherwise seems underspecified. In particular, it's not clear whether a PT_GNU_PROPERTY phdr _must_ be emitted for NT_GNU_PROPERTY_TYPE_0. While it seems a no-brainer to emit it, RHEL's linker already doesn't IIUC, and there are binaries in the wild. Maybe this phdr type is a late addition -- I haven't attempted to dig through the history. For arm64 we don't have this out-of-tree legacy to support, so we can avoid exhausitvely searching for the note: no PT_GNU_PROPERTY -> no note. So, can we do the same for x86, forcing RHEL to carry some code out of tree to support their legacy binaries? Or do we accept that there is already a de facto ABI and try to be compatible with it? >From my side, I want to avoid duplication between x86 and arm64, and keep unneeded complexity out of the ELF loader where possible. Cheers ---Dave [1] https://github.com/hjl-tools/linux-abi/wiki/Linux-Extensions-to-gABI
