| From | Andy Lutomirski <> | Date | Mon, 23 Dec 2019 18:27:40 -0800 | Subject | Re: [RFC PATCH v2 04/10] lib: vdso: get pointer to vdso data from the arch |
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On Mon, Dec 23, 2019 at 6:31 AM Christophe Leroy <christophe.leroy@c-s.fr> 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
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