[Xen-devel] Ping: [PATCH v2] dom0-build: fix build with clang5

[Jan Beulich <jbeulich@xxxxxxxx>]

On 17.07.2019 08:47, Jan Beulich wrote:
> With non-empty CONFIG_DOM0_MEM clang5 produces
> 
> dom0_build.c:344:24: error: use of logical '&&' with constant operand 
> [-Werror,-Wconstant-logical-operand]
>      if ( !dom0_mem_set && CONFIG_DOM0_MEM[0] )
>                         ^  ~~~~~~~~~~~~~~~~~~
> dom0_build.c:344:24: note: use '&' for a bitwise operation
>      if ( !dom0_mem_set && CONFIG_DOM0_MEM[0] )
>                         ^~
>                         &
> dom0_build.c:344:24: note: remove constant to silence this warning
>      if ( !dom0_mem_set && CONFIG_DOM0_MEM[0] )
>                        ~^~~~~~~~~~~~~~~~~~~~~
> 1 error generated.
> 
> Obviously neither of the two suggestions are an option here. Oddly
> enough swapping the operands of the && helps, while e.g. casting or
> parenthesizing doesn't. Another workable variant looks to be the use of
> !! on the constant.
> 
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> ---
> v2: Also adjust the Arm incarnation of the same construct.
> ---
> I'm open to going the !! or yet some different route (but not really the
> suggested strlen() one). No matter which one we choose, I'm afraid it is
> going to remain guesswork what newer (and future) versions of clang will
> choke on.

I guess the disagreement on how to exactly address the issue has
stalled this. But I think we should rather have _some_ (e.g.
this) solution in the repo, than continue to ship versions which
don't build. People wanting to beautify the code further could
then submit incremental patches.

Jan

> --- a/xen/arch/arm/domain_build.c
> +++ b/xen/arch/arm/domain_build.c
> @@ -2125,7 +2125,7 @@ int __init construct_dom0(struct domain
>   
>       printk("*** LOADING DOMAIN 0 ***\n");
>   
> -    if ( !dom0_mem_set && CONFIG_DOM0_MEM[0] )
> +    if ( CONFIG_DOM0_MEM[0] && !dom0_mem_set )
>           parse_dom0_mem(CONFIG_DOM0_MEM);
>   
>       if ( dom0_mem <= 0 )
> --- a/xen/arch/x86/dom0_build.c
> +++ b/xen/arch/x86/dom0_build.c
> @@ -341,7 +341,7 @@ unsigned long __init dom0_compute_nr_pag
>       unsigned long avail = 0, nr_pages, min_pages, max_pages;
>       bool need_paging;
>   
> -    if ( !dom0_mem_set && CONFIG_DOM0_MEM[0] )
> +    if ( CONFIG_DOM0_MEM[0] && !dom0_mem_set )
>           parse_dom0_mem(CONFIG_DOM0_MEM);
>   
>       for_each_node_mask ( node, dom0_nodes )
> 


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