Re: [PATCH] i386/kvm: Fix kvm_enable_x2apic link error in non-KVM builds

[Paolo Bonzini <pbonzini@redhat.com>]

On 11/13/24 15:49, Phil Dennis-Jordan wrote:
> It appears that existing call sites for the kvm_enable_x2apic()
> function rely on the compiler eliding the calls during optimisation
> when building with KVM disabled, or on platforms other than Linux,
> where that function is declared but not defined.
> 
> This fragile reliance recently broke down when commit b12cb38 added
> a new call site which apparently failed to be optimised away when
> building QEMU on macOS with clang, resulting in a link error.

That's weird, can you check the preprocessor output?  The definition
of kvm_irqchip_in_kernel() should be just "false" on macOS, in fact
even the area you're changing should be simplified like

diff --git a/target/i386/kvm/kvm_i386.h b/target/i386/kvm/kvm_i386.h
index 9de9c0d3038..7edb154a16e 100644
--- a/target/i386/kvm/kvm_i386.h
+++ b/target/i386/kvm/kvm_i386.h
@@ -13,8 +13,7 @@

  #include "sysemu/kvm.h"

-#ifdef CONFIG_KVM
-
+/* always false if !CONFIG_KVM */
  #define kvm_pit_in_kernel() \
      (kvm_irqchip_in_kernel() && !kvm_irqchip_is_split())
  #define kvm_pic_in_kernel()  \
@@ -22,14 +21,6 @@
  #define kvm_ioapic_in_kernel() \
      (kvm_irqchip_in_kernel() && !kvm_irqchip_is_split())

-#else
-
-#define kvm_pit_in_kernel()      0
-#define kvm_pic_in_kernel()      0
-#define kvm_ioapic_in_kernel()   0
-
-#endif  /* CONFIG_KVM */
-
  bool kvm_has_smm(void);
  bool kvm_enable_x2apic(void);

Paolo

> 
> Signed-off-by: Phil Dennis-Jordan <phil@philjordan.eu>
> ---
>   target/i386/kvm/kvm_i386.h | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/target/i386/kvm/kvm_i386.h b/target/i386/kvm/kvm_i386.h
> index 9de9c0d3038..7ce47388d90 100644
> --- a/target/i386/kvm/kvm_i386.h
> +++ b/target/i386/kvm/kvm_i386.h
> @@ -21,17 +21,18 @@
>       (kvm_irqchip_in_kernel() && !kvm_irqchip_is_split())
>   #define kvm_ioapic_in_kernel() \
>       (kvm_irqchip_in_kernel() && !kvm_irqchip_is_split())
> +bool kvm_enable_x2apic(void);
>   
>   #else
>   
>   #define kvm_pit_in_kernel()      0
>   #define kvm_pic_in_kernel()      0
>   #define kvm_ioapic_in_kernel()   0
> +#define kvm_enable_x2apic()      0
>   
>   #endif  /* CONFIG_KVM */
>   
>   bool kvm_has_smm(void);
> -bool kvm_enable_x2apic(void);
>   bool kvm_hv_vpindex_settable(void);
>   bool kvm_enable_hypercall(uint64_t enable_mask);
>