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

[Mark Wielaard]

On Tue, 2020-04-14 at 17:25 +0200, Mark Wielaard wrote:
> 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...

OK, I found a workaround, as attached.
It feels a bit like a hack, but seems to do what is expected.

Cheers,

Mark
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