Re: ZFS: i/o error - all block copies unavailable after upgrading to r225312

on 10/09/2011 10:32 Andriy Gapon said the following:
> I am now investigating what looks like a miscompilation of the code by *gcc*
> after applying the patch.  It seems that -mrtd option is to blame.
> I have found an older discussion about the -mrtd option causing trouble with clang:
> http://lists.freebsd.org/pipermail/freebsd-current/2011-August/026263.html
> There was a patch that made clang happy without disabling the flag, so I wonder
> if I made some subtle mistake in my patch.  Or maybe it's better to disable mrtd
> altogether for the zfs boot blocks, just to stay on the safe side.

Actually, removing either -mrtd _or_ -fno-unit-at-a-time produces the correct
code.  Puzzled.

> Some technical details in the form of a diff with some superimposed comments:
> --- /home/avg/tmp/vdev_read_phys-mrtd.s	2011-09-10 01:50:54.500620864 +0300
> +++ /home/avg/tmp/vdev_read_phys-no-mrtd.s	2011-09-10 01:49:59.157701373 +0300
> _at__at_ -29,16 +29,17 _at__at_
> 	... <- in the code before this %edi gets assigned a pointer to a function
>  	movl	60(%ecx), %eax
>  	movl	%eax, 24(%esp)
>  	movl	%ecx, 20(%esp)
> +	movl	%edi, %ecx  <- non-mrtd code saves the pointer
>  	popl	%ebx
>  	popl	%esi
>  	popl	%edi <- %edi gets over-written with an unrelated value
>  	popl	%ebp
> -	jmp	*%edi  <- mrtd code calls some garbage code
> +	jmp	*%ecx  <- non-mrtd code calls the correct code
>  .L601:
>  	movl	$5, %eax
>  	popl	%ebx
>  	popl	%esi
>  	popl	%edi
>  	popl	%ebp
> -	ret	$24
> +	ret
> 
> The problem is in the patched vdev_read_phys function in zfsimpl.c.
> Unpatched version of the function doesn't seem to be affected.
> 
> Any help/ideas will be greatly appreciated!
> 


-- 
Andriy Gapon