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Re: [Qemu-ppc] [PATCH v3] linux-user: elf: mmap all the target-pages of

From: Laurent Vivier
Subject: Re: [Qemu-ppc] [PATCH v3] linux-user: elf: mmap all the target-pages of hostpage for data segment
Date: Wed, 29 Aug 2018 11:33:50 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1

Le 29/08/2018 à 11:23, Shivaprasad G Bhat a écrit :
> If the hostpage size is greater than the TARGET_PAGESIZE, the
> target-pages of size TARGET_PAGESIZE are marked valid only till the
> length requested during the elfload. The glibc attempts to consume unused
> space in the last page of data segment(__libc_memalign() in
> elf/dl-minimal.c). If PT_LOAD p_align is greater than or
> equal to hostpage size, the GLRO(dl_pagesize) is actually the host pagesize
> as set in the auxillary vectors. So, there is no explicit mmap request for
> the remaining target-pages on the last hostpage. The glibc assumes that
> particular space as available and subsequent attempts to use
> those addresses lead to crash as the target_mmap has not marked them valid
> for those target-pages.
> The issue is seen when trying to chroot to 16.04-x86_64 ubuntu on a PPC64
> host where the fork fails to access the thread_id as it is allocated on a
> page not marked valid. The recent glibc doesn't have checks for thread-id in
> fork, but the issue can manifest somewhere else, none the less.
> The fix here is to map all the target-pages of the hostpage during the
> elfload if the p_align is greater than or equal to hostpage size, for
> data segment to allow the glibc for proper consumption.
> Signed-off-by: Shivaprasad G Bhat <address@hidden>
> ---
> v2: https://lists.gnu.org/archive/html/qemu-devel/2018-08/msg05943.html
> Changes from v2:
>     - Simplified the macro as suggested.
>     - Fixed some grammatical error in commit message.
> v1: https://lists.gnu.org/archive/html/qemu-devel/2018-08/msg05730.html
> Changes from v1:
>    - Made the conditionals consistent with the commit "33143c446e" and
>      changed the commit message accordingly.
>  linux-user/elfload.c |   10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)

Reviewed-by: Laurent Vivier <address@hidden>

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