Hi Maciej, On Sun, 2025-05-04 at 12:11 +0100, Maciej W. Rozycki wrote: > > 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.
>From my personal experience, qemu-user has various issues that don't exist on qemu-system. So, if you're experiencing a qemu-related bug in qemu-user, it's always worth verifying it with qemu-system. > 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. Could you point me to the bug report in question? I would like to look into it and see if it is alpha-specific. > > > 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. Aha, I wasn't aware that the original cause for the removal of non-BWX support was due to issue with RCU. I thought the original motivation was that non-BWX Alpha doesn't support byte-access which Linus called a design mistake. Adrian -- .''`. John Paul Adrian Glaubitz : :' : Debian Developer `. `' Physicist `- GPG: 62FF 8A75 84E0 2956 9546 0006 7426 3B37 F5B5 F913
