Hi Dave,
Thanks for your reply.
Maybe I wasn't being entirely clear; the call to mincore() itself succeeded,
i.e. returned 0.
However, when the result array is checked, one or more of the pages are not in
memory.
If we have a look at commit bc8698fd, part of the commit comment says:
> we should also check that the pages are mapped, through the passed mvec
> array. This patch
> also adds this verification.
I think the code that part of the code the comment refers to is this:
> for (i = 0; i < (len + PAGE_SIZE - 1) / PAGE_SIZE; i++)
> {
> if (!(mvec[i] & 1)) return -1;
> }
I'm not sure this is correct. According to the man page for mincore:
> mincore() returns a vector that indicates whether pages of the
> calling process's virtual memory are resident in core (RAM), and so
> will not cause a disk access (page fault) if referenced.
Is this what the author intended to check?
Furthermore, the man page states hat mincore() can return
> ENOMEM addr to addr + length contained unmapped memory.
Thus it looks to me as if mincore() already returns an error code for what the
comment says the block above is checking for.
This is a little out of my comfort zone so I may be talking nonsense, but maybe
have a look at it?
- Daniel
-----Original Message-----
From: Dave Watson [mailto:davejwat...@fb.com]
Sent: 16 January 2018 19:18
To: Daniel Vassdal <d...@meshtech.no>
Cc: Libunwind-devel@nongnu.org
Subject: Re: [Libunwind-devel] mincore_validate fails sometimes
On 01/15/18 12:00 PM, Daniel Vassdal wrote:
> We have an issue where on Yocto Morty 2.2 mincore_validate() sometimes
> unexpectedly returns -1.
> This seems to happen most often directly after the system has been booted.
Do you know what the errno is when it returns -1? Is there some condition we
should be checking for?
> The check that fails is
> > if (!(mvec[i] & 1)) return -1;
>
> The reason I suspect this is a libunwind problem is that when HAVE_MINCORE
> isn't defined, it works well.
> This workaround is sufficient for us, but in case this indeed is a bug I
> figured I'd let you guys know.
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