[PATCH] xen: move xen_setup_callback_vector() definition to include/xen/hvm.h

[Vitaly Kuznetsov]

Kbuild test robot reports the following problem on ARM:

>> drivers/xen/events/events_base.c:1664:6: warning: no previous prototype
  for 'xen_setup_callback_vector' [-Wmissing-prototypes]
1664 | void xen_setup_callback_vector(void) {}
|      ^~~~~~~~~~~~~~~~~~~~~~~~~
The problem is that xen_setup_callback_vector is a x86 only thing, its
definition is present in arch/x86/xen/xen-ops.h but not on ARM. In
events_base.c we have a stub for !CONFIG_XEN_PVHVM but it is not
declared as 'static'.

On x86 the situation is hardly better: drivers/xen/events/events_base.c
doesn't include 'xen-ops.h' from arch/x86/xen/, it includes its namesake
from include/xen/ so we also get the 'no previous prototype' warning.

Currently, xen_setup_callback_vector() has two call sites: one in
drivers/xen/events_base.c and another in arch/x86/xen/suspend_hvm.c. The
former is placed under #ifdef CONFIG_X86 and the later is only compiled
in when CONFIG_XEN_PVHVM.

Resolve the issue by moving xen_setup_callback_vector() declaration to
arch neutral 'include/xen/hvm.h' as the implementation lives in arch
neutral drivers/xen/events/events_base.c.

Reported-by: kbuild test robot <lkp@xxxxxxxxx>
Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
---
- The patch needs to be applied on top of 'x86/xen: Split HVM vector callback
 setup and interrupt gate allocation' ('tip/entry' branch currently). This
 patch doesn't introduce the issue (and that's why I don't add 'Fixes:' tag)
 but it renames xen_callback_vector() -> xen_setup_callback_vector().
---
 arch/x86/xen/suspend_hvm.c | 1 +
 arch/x86/xen/xen-ops.h     | 1 -
 include/xen/hvm.h          | 2 ++
 3 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/xen/suspend_hvm.c b/arch/x86/xen/suspend_hvm.c
index 5152afe16876..9d548b0c772f 100644
--- a/arch/x86/xen/suspend_hvm.c
+++ b/arch/x86/xen/suspend_hvm.c
@@ -2,6 +2,7 @@
 #include <linux/types.h>
 
 #include <xen/xen.h>
+#include <xen/hvm.h>
 #include <xen/features.h>
 #include <xen/interface/features.h>
 
diff --git a/arch/x86/xen/xen-ops.h b/arch/x86/xen/xen-ops.h
index 1cc1568bfe04..937a53e73ea5 100644
--- a/arch/x86/xen/xen-ops.h
+++ b/arch/x86/xen/xen-ops.h
@@ -55,7 +55,6 @@ void xen_enable_sysenter(void);
 void xen_enable_syscall(void);
 void xen_vcpu_restore(void);
 
-void xen_setup_callback_vector(void);
 void xen_hvm_init_shared_info(void);
 void xen_unplug_emulated_devices(void);
 
diff --git a/include/xen/hvm.h b/include/xen/hvm.h
index 0b15f8cb17fc..b7fd7fc9ad41 100644
--- a/include/xen/hvm.h
+++ b/include/xen/hvm.h
@@ -58,4 +58,6 @@ static inline int hvm_get_parameter(int idx, uint64_t *value)
 #define HVM_CALLBACK_VECTOR(x) (((uint64_t)HVM_CALLBACK_VIA_TYPE_VECTOR)<<\
 		HVM_CALLBACK_VIA_TYPE_SHIFT | (x))
 
+void xen_setup_callback_vector(void);
+
 #endif /* XEN_HVM_H__ */
-- 
2.25.4