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Re: versioning of _Unwind_*() symbols

David Mosberger wrote:
Why are the _Unwind_*() symbols being versioned?
Do the GCC developers care about C++ ABI compatibility?

Yes, we care about C++ ABI compatibility.

I am not a library expert, so I don't know all of the ramifications of versioning symbols, but my understanding is that it is standard practice to version symbols exported by standard shared libraries. If we ever find a mistake, and need to fix a bug or change an interface, then the versioning helps us ensure that programs and/or shared libraries linked against the old version of the function still get the old version of the function.

The situation here is a bit special. We added routines to libgcc which are required by C++ ABI. Then you contributed patches to remove them from libgcc and replace them with equivalent versions from libunwind. Unfortunately, this means anything linked against an old version of libgcc can no longer find the old routines they need. This implies that removing the routines from libgcc was wrong.

Note that glibc does the same thing as libgcc, it versions all exported standard functions put in Suppose someone writes their own memcpy function which is better than the one in, and then relinks to remove the glibc memcpy function. What happens? Programs linked against the old no longer work, because they can't find the glibc versioned mempcy function anymore. It seems to make sense that relinking glibc to remove functions is wrong, and by extension, it is also wrong for libgcc.

So it seems that libgcc wasn't doing anything wrong, rather our attempt to remove functions from libgcc to save space was wrong. We can remove them from libgcc.a, but not from

This seems to match with Mark's suggestion of putting the functions back in to maintain backwards compatibility.
Jim Wilson, GNU Tools Support,

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