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References: <20171228180814.9749-1-lukeshu@lukeshu.com>
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From: Laurent Vivier <laurent@vivier.eu>
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Date: Fri, 9 Mar 2018 21:26:56 +0100
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Subject: Re: [Qemu-devel] [PATCH 04/10] linux-user: init_guest_space:
 Correctly handle guest_start in commpage initialization
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To: Luke Shumaker <lukeshu@lukeshu.com>, qemu-devel@nongnu.org
Cc: Luke Shumaker <lukeshu@parabola.nu>, Riku Voipio <riku.voipio@iki.fi>

Le 28/12/2017 à 19:08, Luke Shumaker a écrit :
> From: Luke Shumaker <lukeshu@parabola.nu>
> 
> init_guest_commpage  needs to check if the mapped space, which ends at
> real_start+real_size overlaps with where it needs to put the commpage,
> which is (assuming sane qemu_host_page_size) guest_base + 0xffff000, where
> guest_base is real_start - guest_start.
> 
>     [guest_base][       0xffff0000      ][commpage]
>     [guest_base][guest_start][real_size] [commpage]
>     [       real_start      ][real_size] [commpage]
>                                         ^
>                                  fail if this gap < 0
> 
> Since init_guest_commpage wants to do everything relative to guest_base
> (rather than real_start), it obviously needs to be comparing 0xffff0000
> against guest_start+real_size, not just real_size.
> 
> This bug has been present since 806d102141b99d4f1e55a97d68b7ea8c8ba3129f in
> 2012, but guest_start is usually 0, and prior to v2.11 real_size was
> usually much smaller than 0xffff0000, so it was uncommon for it to have
> made a difference.
> 
> Signed-off-by: Luke Shumaker <lukeshu@parabola.nu>
> ---
>  linux-user/elfload.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Applied to my 'linux-user-for-2.12' branch.

Thanks,
Laurent