Re: [Xen-devel] [PATCH] x86: fix off-by-one error when printing memory ranges

[Wei Liu <wl@xxxxxxx>]

On Wed, Feb 05, 2020 at 11:45:39AM +0000, Wei Liu wrote:
> On Wed, Feb 05, 2020 at 09:12:50AM +0100, Jan Beulich wrote:
> > On 04.02.2020 18:19, Wei Liu wrote:
> > > On Tue, Feb 04, 2020 at 06:07:00PM +0100, Jan Beulich wrote:
> > >> On 04.02.2020 17:55, Wei Liu wrote:
> > >>> Signed-off-by: Wei Liu <liuwe@xxxxxxxxxxxxx>
> > >>> ---
> > >>>  xen/arch/x86/e820.c | 2 +-
> > >>>  1 file changed, 1 insertion(+), 1 deletion(-)
> > >>>
> > >>> diff --git a/xen/arch/x86/e820.c b/xen/arch/x86/e820.c
> > >>> index b9f589cac3..d67387f137 100644
> > >>> --- a/xen/arch/x86/e820.c
> > >>> +++ b/xen/arch/x86/e820.c
> > >>> @@ -94,7 +94,7 @@ static void __init print_e820_memory_map(struct 
> > >>> e820entry *map, unsigned int ent
> > >>>      for (i = 0; i < entries; i++) {
> > >>>          printk(" %016Lx - %016Lx ",
> > >>>                 (unsigned long long)(map[i].addr),
> > >>> -               (unsigned long long)(map[i].addr + map[i].size));
> > >>> +               (unsigned long long)(map[i].addr + map[i].size) - 1);
> > >>
> > >> Why was this an error? If we used [,] like Linux does - sure.
> > >> But we don't. The presentation, without looking at the source,
> > >> simply leaves open whether this was meant to be [,] or [,).
> > >> And it continues to be left open with the adjustment made.
> > >>
> > > 
> > > Well, Linux's representation is not what is normally done in math
> > > either.
> > > 
> > > It is like
> > > 
> > >   Xen: [mem 0x0000000000000000-0x000000000009efff] usable
> > > 
> > > Note it is using '-', not ','. And there is "mem" at the beginning.
> > > 
> > > I have always interpreted the [] pair as something to enclose the range,
> > > not of mathematically meaning.
> > > 
> > > If you want, I can change Xen's format string to "[%016Lx, %016Lx]".
> > 
> > I think this would make things less ambiguous, yes. But my primary
> > request here is to have neither "fix" nor "error" nor anything
> > alike in the title or description.
> 
> OK. I can certainly change the subject line to
> 
>   x86: subtract 1 when printing e820 ranges

If I hear no further objections I will commit this patch with the above
subject line today.

Wei.

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