On Mon, Oct 15, 2018 at 07:27:43PM -0400, Nicolas Pitre wrote: > It's hard to see what that commit was actually fixing, but the operands > usage is wrong as explained already. Maybe the generated code has been > OK for all those years but that is due to luck rather than correctness. ... > No idea. Maybe Russell remembers? > Maybe digging into the mailing list archive might tell.
I found this as a reply to the patch by Mikael Pettersson: I've tested and verified that this bit enables a gcc-4.5 compiled kernel to boot on TS-119 (Kirkwood) when combined with my fix for __naked. With neither or only one of the patches applied, the kernel oopses hard in copy_user_page() as it tries to start /sbin/init. ... - the asm() bodies of these __naked functions have inadequate input parameter constraints, in particular they fail to declare any dependencies on the functions' formal parameters; gcc-4.5 sees this and skips the parameter setup before calling these functions, causing runtime crashes; Khem's patch (this one) fixes that (copypage-xscale.c already had correct asm() constraints so it works with only the __naked fix, these other copypage-*.c files need both patches to work) So, while wrong to the GCC manual, it's fixing a bug that is present with gcc-4.5 and who-knows what other GCC versions. Reverting the commit has the chance to cause regressions with GCC. It looks like any change here needs to be validated on a range of GCC versions, because there are versions of GCC known not to follow it's manual! -- RMK's Patch system: http://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up According to speedtest.net: 11.9Mbps down 500kbps up