On 17 December 2024 11:14:29 CET, Ard Biesheuvel <ardb@xxxxxxxxxx> wrote: >On Tue, 17 Dec 2024 at 11:07, David Woodhouse <dwmw2@xxxxxxxxxxxxx> wrote: >> >> On 17 December 2024 10:54:19 CET, Ard Biesheuvel <ardb@xxxxxxxxxx> wrote: >> >On Tue, 17 Dec 2024 at 10:42, David Woodhouse <dwmw2@xxxxxxxxxxxxx> wrote: >> >> Hm, I am perfectly happy to believe that my memory is failing me, especially when it comes to specifics of i386 assembler code. But are you also telling me that >> >> <https://kernelnewbies.org/FAQ/asmlinkage> is a lie? >> >> >> > >> >It seems wildly out of date, at least. >> > >> >Commit 96a388de5dc53a8b2 from 2007 removed the asmlinkage definition >> >containing regparm(0) from include/asm-i386/linkage.h, and I'm not >> >convinced it was ever sound to conflate linkage with calling >> >convention like that. Today, asmlinkage evaluates to 'extern "C"' when >> >using a C++ compiler, which is also not part of the type. >> > >> >However, I failed to notice that this just moves code around, and only >> >applies to 32-bit in the first place. So I won't waste any more of >> >your time obsessing over this. >> >> Too late :) >> >> You've already made me concerned about what the calling convention *is* for relocate_kernel() on i386. Because if asmlinkage doesn't mean regparm(0) any more and the i386 kernel is still built with -mregparm=3, then how does the asm code (which seems to believe all its arguments are on the stack) actually work? >> >> It seems slightly unlikely that kexec on i386 has just been broken since 2007 but I'm not sure I'd completely rule it out. >> >> So now I guess I have to actually build a 32-bit userspace test case and *test* it. >> >> And that means I no longer have any excuse for not doing all the same cleanups in the i386 version of the code that I've done for x86_64... >> >> Thanks for that :) >> > >Actually, asmlinkage still means regparm(0) on i386, so I'm going to >have to apologise again, for my poor git foo this time. Heh, no problem. I'm pleased to find my memory wasn't failing me after all, so I might have a bit more time left before they put me out to pasture. I'll take that win :)
