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Re: [Xen-devel] [PATCH] x86/dom0-build: fix build with clang5
- To: Jan Beulich <JBeulich@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Mon, 15 Jul 2019 14:49:54 +0100
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- Cc: Wei Liu <wl@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Delivery-date: Mon, 15 Jul 2019 13:50:08 +0000
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On 15/07/2019 11:35, 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>
> ---
> I'm open to going the !! or yet some different route. 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.
>
> --- 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);
First and foremost, there is an identical construct on the ARM side,
which wants an equivalent adjustment.
As to the change, I'm going to suggest what I suggested instead of this
the first time around, which is strlen(CONFIG_DOM0_MEM) to make the
logic easier to follow.
~Andrew
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