On 11/05/2017 01:18 PM, Nicholas Piggin wrote:

> There was a recent change to move to 128TB address space by default,
> and option for 512TB addresses if explicitly requested.

Do you have a commit hash for the introduction of 128TB by default?  Thanks.

> Your brk request asked for > 128TB which the kernel gave it, but the
> address limit in the paca that the SLB miss tests against was not
> updated to reflect the switch to 512TB address space.
> 
> Why is your brk starting so high? Are you trying to test the > 128TB
> case, or maybe something is confused by the 64->128TB change? What's
> the strace look like if you run on a distro or <= 4.10 kernel?

I think it is a consequence of running with an explicit loader 
invocation.  With that, the heap is placed above ld.so, which can be 
quite high in the address space.

I'm attaching two runs of cat, one executing directly as /bin/cat, and 
one with /lib64/ld64.so.1 /bin/cat.

Fortunately, this does *not* apply to PIE binaries (also attached). 
However, explicit loader invocations are sometimes used in test suites 
(not just for glibc), and these sporadic test failures are quite annoying.

Do you still need the strace log?  And if yes, of what exactly?

> Something like the following patch may help if you could test.

Okay, this will take some time.

Thanks,
Florian