This is the mail archive of the glibc-bugs@sourceware.org mailing list for the glibc project.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

[Bug libc/12518] memcpy acts randomly (and differently) with overlapping areas


http://sourceware.org/bugzilla/show_bug.cgi?id=12518

--- Comment #29 from Ondrej Bilka <neleai at seznam dot cz> ---
On Mon, Aug 12, 2013 at 05:19:54PM +0000, tudorb at gmail dot com wrote:
> --- Comment #28 from Tudor Bosman <tudorb at gmail dot com> ---
> FYI, this bug has bitten me in a different way: memcpy() copying backwards
> defeats the MADV_SEQUENTIAL flag to madvise(). A trivial file copier
> implementation (mmap source, mmap destination, set MADV_SEQUENTIAL, memcpy from
> source to destination) would perform much worse on machines that support SSSE3
> than on machines that don't because of this bug.
>
Wait, do you have overlapping source and destination areas? If so then a
backward copy is necessary.

Or is backward copy called for not overlapping areas? 
I have a patch that could call backward copy only if src-n < dest < src+n
holds.

> (Before anyone tells me that I should copy files using read() and write(), my
> actual usage pattern was more complex, but the details are irrelevant.)
> 
> -- 
> You are receiving this mail because:
> You are on the CC list for the bug.

-- 
You are receiving this mail because:
You are on the CC list for the bug.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]