RE: [PATCH 1/4] target/ppc: Code motion required to build disabling tcg

From: Bruno Piazera Larsen <bruno.larsen@eldorado.org.br>
To: David Gibson <david@gibson.dropbear.id.au>,
	Fabiano Rosas <farosas@linux.ibm.com>
Cc: Thomas Huth <thuth@redhat.com>,
	"qemu-devel@nongnu.org" <qemu-devel@nongnu.org>,
	Andre Fernando da Silva <andre.silva@eldorado.org.br>,
	Lucas Mateus Martins Araujo e Castro
	<lucas.araujo@eldorado.org.br>,
	Fernando Eckhardt Valle <fernando.valle@eldorado.org.br>,
	"qemu-ppc@nongnu.org" <qemu-ppc@nongnu.org>,
	"lagarcia@br.ibm.com" <lagarcia@br.ibm.com>,
	Matheus Kowalczuk Ferst <matheus.ferst@eldorado.org.br>,
	Luis Fernando Fujita Pires <luis.pires@eldorado.org.br>
Subject: RE: [PATCH 1/4] target/ppc: Code motion required to build disabling tcg
Date: Mon, 19 Apr 2021 14:40:35 +0000	[thread overview]
Message-ID: <CP2PR80MB44998EBF7704B13C79081093C7499@CP2PR80MB4499.lamprd80.prod.outlook.com> (raw)

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> > > * move gen_write_xer and gen_read_xer into cpu_init.c, as they're
> > > used for some sprs, and whatever needs to be moved with it
> >
> > I'd leave them where they are currently. Instead what I think we should
> > do is to find a way to not need the uea/oea/hea|read/write callbacks
> > with KVM.
> >
> > Maybe extract a function from _spr_register that sets what is common for
> > both tcg and kvm (num, name, initial_value, AFAICT). Then alter the
> > gen_spr* functions to first create all registers and then call both
> > configs to supplement:
> >
> > //tcg.c
> > static void tcg_gen_spr_generic(CPUPPCState *env)
> > {
> >     // these only set the callbacks
> >     spr_register(env, SPR_FOO,
> >                  SPR_NOACCESS, SPR_NOACCESS,
> >                  &spr_read_foo, &spr_write_foo);
> >     spr_register(env, SPR_BAR,
> >                  SPR_NOACCESS, SPR_NOACCESS,
> >                  &spr_read_bar, &spr_write_bar);
> > }
> >
> > //kvm.c
> > static void kvm_gen_spr_generic(CPUPPCState *env)
> > {
> >     // these only set one_reg_id
> >     spr_register_kvm(env, SPR_FOO, KVM_REG_PPC_FOO);
> >     spr_register_kvm(env, SPR_BAR, KVM_REG_PPC_BAR);
> > }
>
> I really dislike the idea above - it'd be way too easy for KVM and TCG
> to get out of sync.  Instead make spr_register() itself a macro if
> necessary, so it just ignores the access functions in the !TCG case.

What I was doing was to only register the spr once, and use the
accel-specific functions to set the relevant attributes, so spr_common
wouldn't need to where (and if) spr_read_* exists or not.
Would this work?

Just ignoring the read and write functions means we still need
to compile them, or at least stub them, otherwise we'd get linker
problems. And ifdef'ing them out of the calls would be quite a
pain to understand the code later on.

Bruno Piazera Larsen

Instituto de Pesquisas ELDORADO<http://clickemailmkt.eldorado.org.br/ls/click?upn=UPoxpeIcHnAcbUZyo7TTaswyiVb1TXP3jEbQqiiJKKGsxOn8hBEs5ZsMLQfXkKuKXZ7MVDg0ij9eG8HV4TXI75dBzDiNGLxQ8Xx5PzCVNt6TpGrzBbU-2Biu0o69X5ce-2FW-2FOk1uUipuK0fZnWXJEgbRw-3D-3DJY4T_wWk-2BG6VvNBoa1YzxYjhCdFS9IfANIaBzDSklR1NyyrKOI1wj0P-2BdBFcuO4FnHcsA1MyHu0ly1Yt3oDMp7KKdJPM68iKuI2jiRH5v4B0d8wf3chU3qy5n5iXWnW1QjSaNFHOgELzxaP-2FnesTeBgJ5dFkjH4f279sVQpOtyjw5xAqj34M6pgNRAxVvuXif4IWDcVzXg1FzfYlEfkKzr9vvpA3Hg8kitwMtlU3zwbQUBCgL30fQoJPcRPMGKyOY8RmoAlXNqTJYDYIvqmfnI7KLUvw6vKB5R-2B5q1FJRAzX7H-2BmF0NnDET6jMLuIqtCcVIch>

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