Date: Fri, 20 Mar 2020 23:18:56 +0100 From: Andreas Dröscher <musl@...free.ch> To: Rich Felker <dalias@...c.org> Cc: musl@...ts.openwall.com Subject: Re: mips32 little endian -ENOSYS is not -(-ENOSYS) Am 20.03.20 um 17:34 schrieb Rich Felker: > On Wed, Mar 11, 2020 at 07:08:48PM -0400, Rich Felker wrote: >> 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. > > I've pushed a version of this upstream now, a long with a lot of other > commits that had backed up in my queue. Please let me know if this > does or doesn't fix the issues with mips on old kernels. > Sorry for now sending an update in a timely manner. I've tested your patches and they definitely get me to the point I had with my manual changes. However, the incompatibilities I reported earlier stil need to be ironed out. Sadly I got sidetracked by another project. There was no progress in the past week. I’m planning to pick up the task on Monday. I was wondering if the inclusion of our fixes for a 13-year-old kernel benefits anyone except my niche use case. Andreas
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