Date: Wed, 11 Mar 2020 19:08:48 -0400 From: Rich Felker <dalias@...c.org> To: Andreas Dröscher <musl@...free.ch> Cc: musl@...ts.openwall.com Subject: Re: mips32 little endian -ENOSYS is not -(-ENOSYS) On Wed, Mar 11, 2020 at 10:08:11PM +0100, Andreas Dröscher wrote: > Am 11.03.20 um 03:18 schrieb Rich Felker: > >On Wed, Mar 11, 2020 at 03:08:22AM +0100, Andreas Dröscher wrote: > >>The current implementation of __syscall5, __syscall6 and __syscall7 > >>(those use caller saved registers) violate the calling conventions > >>of MIPS32 Linux Kernels prior 2.6.35. Those were assuming that the > >>instruction immediately preceding the SYSCALL instruction was an > >>instruction for loading the syscall number. > >> > >>I’ll will try to rearrange the stack pushes to accommodate this > >>requirement and report back if I manage to come up with something > >>presentable. > > > >Uhg, so commit 604f8d3d8b08ee4f548de193050ef93a7753c2e0 was probably > >wrong and there was a reason for the nonsensical code it removed: > >making old broken kernels happy. I'm not sure if you can just revert > >it or need to make new changes. > > > >Do you know if this "rule" applies to n32/n64 too or just o32? > > I've reverted 604f8d3d8b08ee4f548de193050ef93a7753c2e0 and additionally > replaced all: > return r7 ? -r2 : r2; > with > return (r7 && r2 > 0) ? -r2 : r2; > > My software stack (built with OE-Core Zeus) now works almost flawlessly. > Some Daemons have hiccups but those most likely come from source > that expects syscalls to always succeed and on my system they are > simply missing. > > Thank you for your helping to sort this out. > > You asked about n32/n64. I am not familiar with more modern MIPS Architectures. > Therefore I can't give any informed answer. I found some documentation: > https://www.linux-mips.org/wiki/Syscall but it does not give a > definitive answer. It just points towards "all 3 mips are effected > by the ordering requirement". I'm posting a patch series now. Rich
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