[PATCH] target/i386: Re-introduce few KVM stubs for Clang debug builds

[Philippe Mathieu-Daudé <philmd@xxxxxxxxxx>]

Since commits 3adce820cf..ef1cf6890f, When building on
a x86 host configured as:

  $ ./configure --cc=clang \
    --target-list=x86_64-linux-user,x86_64-softmmu \
    --enable-debug

we get:

  [71/71] Linking target qemu-x86_64
  FAILED: qemu-x86_64
  /usr/bin/ld: libqemu-x86_64-linux-user.fa.p/target_i386_cpu.c.o: in function `cpu_x86_cpuid':
  cpu.c:(.text+0x1374): undefined reference to `kvm_arch_get_supported_cpuid'
  /usr/bin/ld: libqemu-x86_64-linux-user.fa.p/target_i386_cpu.c.o: in function `x86_cpu_filter_features':
  cpu.c:(.text+0x81c2): undefined reference to `kvm_arch_get_supported_cpuid'
  /usr/bin/ld: cpu.c:(.text+0x81da): undefined reference to `kvm_arch_get_supported_cpuid'
  /usr/bin/ld: cpu.c:(.text+0x81f2): undefined reference to `kvm_arch_get_supported_cpuid'
  /usr/bin/ld: cpu.c:(.text+0x820a): undefined reference to `kvm_arch_get_supported_cpuid'
  /usr/bin/ld: libqemu-x86_64-linux-user.fa.p/target_i386_cpu.c.o:cpu.c:(.text+0x8225): more undefined references to `kvm_arch_get_supported_cpuid' follow
  clang: error: linker command failed with exit code 1 (use -v to see invocation)
  ninja: build stopped: subcommand failed.

'--enable-debug' disables optimizations (CFLAGS=-O0).

While at this (un)optimization level GCC eliminate the
following dead code:

  if (0 && foo()) {
      ...
  }

Clang does not. Therefore restore a pair of stubs for
unoptimized Clang builds.

Reported-by: Kevin Wolf <kwolf@xxxxxxxxxx>
Fixes: 3adce820cf ("target/i386: Remove unused KVM stubs")
Fixes: ef1cf6890f ("target/i386: Allow elision of kvm_hv_vpindex_settable()")
Signed-off-by: Philippe Mathieu-Daudé <philmd@xxxxxxxxxx>
---
 target/i386/kvm/kvm_i386.h | 21 ++++++++++++++++++---
 1 file changed, 18 insertions(+), 3 deletions(-)

diff --git a/target/i386/kvm/kvm_i386.h b/target/i386/kvm/kvm_i386.h
index 55d4e68c34..0b62ac628f 100644
--- a/target/i386/kvm/kvm_i386.h
+++ b/target/i386/kvm/kvm_i386.h
@@ -32,7 +32,6 @@
 
 bool kvm_has_smm(void);
 bool kvm_enable_x2apic(void);
-bool kvm_hv_vpindex_settable(void);
 bool kvm_has_pit_state2(void);
 
 bool kvm_enable_sgx_provisioning(KVMState *s);
@@ -41,8 +40,6 @@ bool kvm_hyperv_expand_features(X86CPU *cpu, Error **errp);
 void kvm_arch_reset_vcpu(X86CPU *cs);
 void kvm_arch_after_reset_vcpu(X86CPU *cpu);
 void kvm_arch_do_init_vcpu(X86CPU *cs);
-uint32_t kvm_arch_get_supported_cpuid(KVMState *env, uint32_t function,
-                                      uint32_t index, int reg);
 uint64_t kvm_arch_get_supported_msr_feature(KVMState *s, uint32_t index);
 
 void kvm_set_max_apic_id(uint32_t max_apic_id);
@@ -60,6 +57,10 @@ void kvm_put_apicbase(X86CPU *cpu, uint64_t value);
 
 bool kvm_has_x2apic_api(void);
 bool kvm_has_waitpkg(void);
+bool kvm_hv_vpindex_settable(void);
+
+uint32_t kvm_arch_get_supported_cpuid(KVMState *env, uint32_t function,
+                                      uint32_t index, int reg);
 
 uint64_t kvm_swizzle_msi_ext_dest_id(uint64_t address);
 void kvm_update_msi_routes_all(void *private, bool global,
@@ -76,6 +77,20 @@ typedef struct kvm_msr_handlers {
 bool kvm_filter_msr(KVMState *s, uint32_t msr, QEMURDMSRHandler *rdmsr,
                     QEMUWRMSRHandler *wrmsr);
 
+#elif defined(__clang__) && !defined(__OPTIMIZE__)
+
+static inline bool kvm_hv_vpindex_settable(void)
+{
+    g_assert_not_reached();
+}
+
+static inline uint32_t kvm_arch_get_supported_cpuid(KVMState *env,
+                                                    uint32_t function,
+                                                    uint32_t index, int reg)
+{
+    g_assert_not_reached();
+}
+
 #endif /* CONFIG_KVM */
 
 void kvm_pc_setup_irq_routing(bool pci_enabled);
-- 
2.41.0