Found on debian stable.

../target/i386/kvm/kvm.c: In function ‘kvm_handle_rdmsr’:
../target/i386/kvm/kvm.c:5345:1: error: control reaches end of non-void function [-Werror=return-type]
 5345 | }
      | ^
../target/i386/kvm/kvm.c: In function ‘kvm_handle_wrmsr’:
../target/i386/kvm/kvm.c:5364:1: error: control reaches end of non-void function [-Werror=return-type]
 5364 | }
---
 target/i386/kvm/kvm.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
index 31f149c9902..ddec27edd5b 100644
--- a/target/i386/kvm/kvm.c
+++ b/target/i386/kvm/kvm.c
@@ -5770,7 +5770,7 @@ static int kvm_handle_rdmsr(X86CPU *cpu, struct kvm_run *run)
         }
     }
 
-    assert(false);
+    g_assert_not_reached();
 }
 
 static int kvm_handle_wrmsr(X86CPU *cpu, struct kvm_run *run)
@@ -5789,7 +5789,7 @@ static int kvm_handle_wrmsr(X86CPU *cpu, struct kvm_run *run)
         }
     }
 
-    assert(false);
+    g_assert_not_reached();
 }
 
 static bool has_sgx_provisioning;
-- 
2.39.2