Re: [Xen-devel] [PATCH] mm: make opt_bootscrub non-init

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Fri, Nov 23, 2018 at 03:30:02PM +0100, Roger Pau Monne wrote:
> LLVM code generation can attempt to load from a variable in the next
> condition of an expression under certain circumstances, thus turning
> the following condition:
> 
> if ( system_state < SYS_STATE_active && opt_bootscrub == BOOTSCRUB_IDLE )
> 
> Into:
> 
> 0xffff82d080223967 <+103>: cmpl   $0x3,0x37b032(%rip) # 0xffff82d08059e9a0 
> <system_state>
> 0xffff82d08022396e <+110>: setb   -0x29(%rbp)
> 0xffff82d080223972 <+114>: cmpl   $0x2,0x228a8b(%rip) # 0xffff82d08044c404 
> <opt_bootscrub>
> 
> Such code will trigger a page fault if system_state >=
> SYS_STATE_active because opt_bootscrub will be unmapped.
> 
> Fix this by making opt_bootscrub non-init, thus preventing the page
> fault. The LLVM bug with the discussion about this issue can be found
> at:
> 
> https://bugs.llvm.org/show_bug.cgi?id=39707
> 
> I haven't been able to find any other instances of such conditional
> expression that uses system_state together with an init variable or
> function.
> 
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

Acked-by: Wei Liu <wei.liu2@xxxxxxxxxx>

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel