On Sun, 4 May 2025, John Paul Adrian Glaubitz wrote: > > I only have non-BWX hardware and I'm not interested in decommissioning it > > or upgrading. There appear to be a few users around, but I seem to be the > > last GCC developer remaining who is willing to do anything about the port. > > It doesn't help that Alpha/QEMU appears broken and produces unreliable > > results, so it'd have to be someone with actual hardware (or willing to > > fix QEMU first). > > What exactly is broken with the QEMU emulation in Alpha? I don't know of any > bugs, but it could be that you have run into the nasty stack alignment issue > in the kernel that was fixed in Linux 6.14.
This was with QEMU in the user emulation mode, causing intermittent failures across the GCC testsuite, so unrelated to any Linux kernel issues. Perhaps the system emulation mode works better, but the GCC testsuite doesn't rely much on syscall emulation and the nature of the failures didn't indicate this aspect of the user emulation mode mattered here. I have reported it at the time and this has led to Magnus being kind enough, following your request, to let me use his BWX Alpha system for verification instead, where no intermittent failures were observed, so again no Linux kernel bugs mattered here (this was last year, well before the fix) and it was QEMU clearly at fault. > > What I was not aware of is the situation with the Alpha backend and the > > need to put out fires there. That non-BWX issue with Linux kernel's RCU > > algorithms was a nasty surprise to me, one I could have dealt with before > > with less time pressure if I knew about it. > > What RCU issue are you talking about? I can only stress that to use Linux on > Alpha, you *must* use kernel 6.14 or later with CONFIG_COMPACTION disabled > otherwise you will run into all kinds of issues. The very RCU issue that prompted the removal of non-BWX support from the kernel last year and then this whole effort of mine. Maciej
