On 11/23/2015 07:43 AM, Chris Adams wrote:
Once upon a time, Michael Eager <ea...@eagerm.com> said:
I'm trying to build an application on CentOS 7 which
can run on older versions of CentOS. I'm running into
problems with versioning of memcpy in Glibc. Executables
built on CentOS 7 require memcpy from glibc-2.14, which
causes the program not to load on systems with older
versions of glibc.
Most shared libraries are "upwards compatible" but not "backwards
compatible" - builds against an old version will run with the new
version, but not the other way around. You've found this with glibc,
but you could also run into it with other libraries.
The situation with memcpy is a bit different. This isn't really a
forward/backward interface compatibility issue.
There was a patch applied to memcpy to improve performance on
some architectures, but it also changed the order in which data was
moved. Some programs were dependent on this and they broke with the
new implementation. These programs did not conform to the non-overlapping
data requirements in memcpy's specification. Programs which did conform
worked with both the new and old implementation.
To prevent non-conforming programs from using the new version of
memcpy, they tagged it with glibc-2.14. Unfortunately, this also
makes conforming programs, which work with either the old or new
implementation from running on systems which have older versions of
glibc.
My online search suggests to add an asm() with a .symver
option to select memcpy from glibc-2.2.5 in each of the
source files which reference memcpy(). This isn't practical
with a program with tens of thousands of source files.
Does anyone have a reasonable solution?
Would it be practical to use mock and build on the oldest version you
want to support? This is how EPEL packages are built for example. It
is targeted at building RPMs, but you can manually use copy-in and
copy-out to do other things.
I'll look into mock.
--
Michael Eager ea...@eagercon.com
1960 Park Blvd., Palo Alto, CA 94306 650-325-8077
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