On Mon, Dec 23, 2019 at 6:31 AM Christophe Leroy
[off-list ref] wrote:

On powerpc, __arch_get_vdso_data() clobbers the link register,
requiring the caller to set a stack frame in order to save it.

As the parent function already has to set a stack frame and save
the link register to call the C vdso function, retriving the
vdso data pointer there is lighter.

I'm confused.  Can't you inline __arch_get_vdso_data()?  Or is the
issue that you can't retrieve the program counter on power without
clobbering the link register?

I would imagine that this patch generates worse code on any
architecture with PC-relative addressing modes (which includes at
least x86_64, and I would guess includes most modern architectures).

--Andy