Undefined reference to mempcy@GLIBC_2.14 when compiling on Linux

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The mempcy@GLIBC_2.14 is called a versioned symbol. Glibc uses them while other runtime libraries like musl do not.

The significance of mempcy@GLIBC_2.14 when compiling on Linux is due to Glibc changing the way memcpy worked back in 2012. memcpy used to copy bytes {begin → end} (low memory address to high memory address). Glibc 2.13 provided an optimized memcpy that copied {end → begin} on some platforms. I believe “some platforms” included Intel machines with SSE4.1. Then, Glibc 2.14 provided a memcpy that restored the {begin → end} behavior.

Some programs depended upon the {begin → end} copy. When programs used overlapping buffers then memcpy produced undefined behavior. In this case a program should have used memmove, but they were getting by due to a copy that occurred {begin → end}. Also see Strange sound on mp3 flash website (due to Adobe Flash), Glibc change exposing bugs (on LWN), The memcpy vs memmove saga and friends.

To fix it it looks like you can add the following to your source code:

__asm__(".symver memcpy,memcpy@GLIBC_2.2.5");

Maybe something like the following. Then include the extra source file in your project.

$ cat version.c

__asm__(".symver memcpy,memcpy@GLIBC_2.2.5");

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