Re: [Qemu-devel] [PATCH uq/master v2 1/2] kvm: reset state from the CPU's reset method

[Paolo Bonzini <pbonzini@redhat.com>]

Il 08/04/2013 14:19, Gleb Natapov ha scritto:
>> > Does this compile with kvm support disabled?

Oops, sorry, I thought I had replied to this email (with "hmm, let me
check").

> Well, it does not:
>   CC    s390x-softmmu/target-s390x/cpu.o
> /users/gleb/work/qemu/target-s390x/cpu.c: In function 's390_cpu_reset':
> /users/gleb/work/qemu/target-s390x/cpu.c:89:9: error: implicit
> declaration of function 'kvm_arch_reset_vcpu'
> [-Werror=implicit-function-declaration]
> /users/gleb/work/qemu/target-s390x/cpu.c:89:9: error: nested extern
> declaration of 'kvm_arch_reset_vcpu' [-Werror=nested-externs]
> cc1: all warnings being treated as errors
> 
> I wonder if it is portable between compilers to rely on code in if(0){} to
> be dropped in all levels of optimizations.

It generally is okay to assume it (I think early GCC 3.x releases had no
-O0 dead-code optimization, but it was a long time ago).  However:

* in QEMU only some files have kvm_enabled() as 0 when KVM is disabled.
 Files that are shared among multiple targets have it defined to
kvm_allowed.  This is not the problem here.

* you still need to define the prototypes for anything you call, of course.

Paolo