[PATCH] lib: Use attribute symver when available to define symbol versioning.

[Mark Wielaard]

Hi,

On Fri, 2020-04-10 at 21:42 +0200, Mark Wielaard wrote:
> GCC 10 introduces a function attribute to define symbol versioning.
> Add a configure check to see if __attribute__((symver)) is supported.
> If it is then define the OLD_VERSION, NEW_VERSION, COMPAT_VERSION
> and COMPAT_VERSION_NEWPROTO macros using just attribute symver,
> attribute alias and typeof function names. And avoid defining symbols
> in asm statements.

Turns out this almost, but not completely work.

> +#define NEW_VERSION(name, version) \
> +  __attribute__((__symver__(#name "@@" #version))) \
> +  __typeof__ ( name ) name ;

Using the two @@ variant keeps the original name in the symbol table,
which will cause that symbol to be doubly marked as a version symbol my
the linker. We really need the tripple @@@ variant which will actually
rename and remove the original non-versioned name. But gcc10
attribute((symver)) only accepts the single and double @ variants.

I am looking how to work around this. The gcc function attribute
documentation implies that you shouldn't use the bare non-versioned
symbol name, but that is precisely what we do (so we don't have to mark
up each symbol, but can simply rely on the linker version map script).

Back to the drawing board...

Cheers,

Mark