Date: Sun, 20 Jul 2014 09:18:33 +0300 From: Stefan Kristiansson <stefan.kristiansson@...nalahti.fi> To: Rich Felker <dalias@...c.org> Cc: musl@...ts.openwall.com Subject: Re: How to build a musl toolchain for or1k On Sat, Jul 19, 2014 at 07:06:56PM -0400, Rich Felker wrote: > On Sun, Jul 20, 2014 at 01:26:29AM +0300, Stefan Kristiansson wrote: > > Mainline kernel is missing support for a couple of features required > > by musl (mostly related to the atomic instructions). I've added > > support for them, but sending out patches for them is yet to be done. > > In the meantime, they are all present in the smp branch of > > git://openrisc.net/stefan/linux. > > What kernel features are needed for atomics to work? I figured it was > mainly a cpu-level issue. Or were changes needed for the kernel to > properly clear the lwa/swa flag on context switch? > It is mainly a cpu-level issue, and there's actually only two patches in that branch that are required for musl to work. 1) There's no way on or1k to determine if a data page fault was a read or write fault other than reading the instruction at the faulting PC and check if it was a store instructions. The atomic store instruction (l.swa) was missing from this check. http://git.openrisc.net/cgit.cgi/stefan/linux/commit/?h=smp&id=a966c95bb10a43cab16e2be97518ad8be0695a95 2) In order to get kernel support for robust_list, there need to be arch specific implementations of the futex_atomic_* operations. These implementations were missing. http://git.openrisc.net/cgit.cgi/stefan/linux/commit/?h=smp&id=d863b0637811dd559363a3f1bf9d966e35b21bab > It would be really nice if the kernel could also trap and emulate > l.lwa/l.swa and perhaps also l.msync so that these features could be > used on old emulators/hardware that lack them. > I agree. > > git clone -b smp git://openrisc.net/stefan/linux > > make ARCH=openrisc musl_defconfig > > make ARCH=openrisc > > What's special in musl_defconfig? :) > Actually very little ;) The support for the atomic instructions is enabled. Stefan
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