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Re: [Libunwind-devel] Re: [PATCH][x86_64] Make address validation a per

From: Arun Sharma
Subject: Re: [Libunwind-devel] Re: [PATCH][x86_64] Make address validation a per thread setting
Date: Thu, 19 Feb 2009 07:50:48 -0800

On Thu, Feb 19, 2009 at 3:45 AM, Mattias Engdegård <address@hidden> wrote:
> msync(2) does not protect against reading from mapped but
> read-protected addresses (MAP_NONE), which are not uncommon on x86_64.
> We recently had a number of crashes resulting from this (although
> libunwind was not directly involved in this case).

Yes - I've seen this particular crash before. But it seems to be
relatively uncommon and most of the bad references were due to issues
that could be handled in libunwind.

Due to the patches that went in during the last year or so, I think
many of those cases are resolved. Remaining x86_64 issues have to do

* Compiler generating incomplete unwind info
* Occasional patches that introduce calls to malloc

Will also benchmark pread(). We have code that's sensitive to unwind
performance. So we tend to use a small (but potentially racy) cache to
avoid getting into the kernel often.


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