Messages in this thread | | | Date | Tue, 16 Oct 2018 14:09:49 +0200 | From | Stefan Agner <> | Subject | Re: [PATCH 2/2] ARM: copypage: do not use naked functions |
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On 16.10.2018 10:33, Russell King - ARM Linux wrote: > 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.
The build system requires at least GCC 4.6 currently, so we do not have to deal with 4.5.
> > 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!
The commit message as well as the above message sounds more like it was a newly introduced behavior in 4.5. I would suggest to at least check 4.6 to make sure it has been corrected.
-- Stefan
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