[Arm-dev] [PATCH v2] config-centos-sig: aarch64: Enable 48 bit VA

Christopher Covington cov at codeaurora.org
Mon Nov 21 13:51:57 UTC 2016


On 11/18/2016 05:34 PM, Jeremy Linton wrote:
> On 11/18/2016 04:29 PM, Jeremy Linton wrote:
>> The current RHELSA kernel is using a 42bit VA which
>> is too limiting for possible near future workloads.
>> Update this to 48 bits. This patch has a dependency
>> on mozjs versions in the distro being patched to
>> work with virtual address spaces >47 bits.
> 
> Just a quick comment. An easy way to verify that the kernel in use has 48bit VA's is to check the /proc/xxx/maps of a userspace process.
> 
> A 48bit VA kernel will place shared libraries into addresses at the top of the userspace address region. For example:
> 
> ffffacbb0000-ffffacbc0000 r-xp 00000000 103:04 33858952 /usr/lib64/libnss_files-2.17.so
> ffffacbc0000-ffffacbd0000 r--p 00000000 103:04 33858952 /usr/lib64/libnss_files-2.17.so
> ffffacbd0000-ffffacbe0000 rw-p 00010000 103:04 33858952 /usr/lib64/libnss_files-2.17.so
> ffffacbf0000-ffffacc30000 r-xp 00000000 103:04 33644605 /usr/lib64/libpcre.so.1.2.0
> ffffacc30000-ffffacc40000 r--p 00030000 103:04 33644605 /usr/lib64/libpcre.so.1.2.0
> ffffacc40000-ffffacc50000 rw-p 00040000 103:04 33644605 /usr/lib64/libpcre.so.1.2.0

How does GNU ld determine VA bits?

Thanks,
Cov

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