x86: identify reset_stack_and_jump() as noreturn

reset_stack_and_jump() is actually a macro, but can effectivly become noreturn
by giving it an unreachable() declaration.

Propagate the 'noreturn-ness' up through the direct and indirect callers.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Tim Deegan <tim@xen.org>
Acked-by: Keir Fraser <keir@xen.org>

xen/arch/x86/domain.c

@@ -133,12 +133,12 @@ void startup_cpu_idle_loop(void)
     reset_stack_and_jump(idle_loop);
 }
 
-static void continue_idle_domain(struct vcpu *v)
+static void noreturn continue_idle_domain(struct vcpu *v)
 {
     reset_stack_and_jump(idle_loop);
 }
 
-static void continue_nonidle_domain(struct vcpu *v)
+static void noreturn continue_nonidle_domain(struct vcpu *v)
 {
     check_wakeup_from_wait();
     mark_regs_dirty(guest_cpu_user_regs());
@@ -1521,13 +1521,11 @@ void context_switch(struct vcpu *prev, struct vcpu *next)
     update_vcpu_system_time(next);
 
     schedule_tail(next);
-    BUG();
 }
 
 void continue_running(struct vcpu *same)
 {
     schedule_tail(same);
-    BUG();
 }
 
 int __sync_local_execstate(void)

xen/arch/x86/hvm/svm/svm.c

@@ -911,7 +911,7 @@ static void svm_ctxt_switch_to(struct vcpu *v)
         wrmsrl(MSR_TSC_AUX, hvm_msr_tsc_aux(v));
 }
 
-static void svm_do_resume(struct vcpu *v) 
+static void noreturn svm_do_resume(struct vcpu *v)
 {
     struct vmcb_struct *vmcb = v->arch.hvm_svm.vmcb;
     bool_t debug_state = v->domain->debugger_attached;

xen/arch/x86/setup.c

@@ -537,7 +537,7 @@ static char * __init cmdline_cook(char *p, char *loader_name)
     return p;
 }
 
-void __init __start_xen(unsigned long mbi_p)
+void __init noreturn __start_xen(unsigned long mbi_p)
 {
     char *memmap_type = NULL;
     char *cmdline, *kextra, *loader;

xen/include/asm-x86/current.h

@@ -59,10 +59,13 @@ static inline struct cpu_info *get_cpu_info(void)
     ((sp & (~(STACK_SIZE-1))) +                 \
      (STACK_SIZE - sizeof(struct cpu_info) - sizeof(unsigned long)))
 
-#define reset_stack_and_jump(__fn)              \
-    __asm__ __volatile__ (                      \
-        "mov %0,%%"__OP"sp; jmp %c1"            \
-        : : "r" (guest_cpu_user_regs()), "i" (__fn) : "memory" )
+#define reset_stack_and_jump(__fn)                                      \
+    ({                                                                  \
+        __asm__ __volatile__ (                                          \
+            "mov %0,%%"__OP"sp; jmp %c1"                                \
+            : : "r" (guest_cpu_user_regs()), "i" (__fn) : "memory" );   \
+        unreachable();                                                  \
+    })
 
 #define schedule_tail(vcpu) (((vcpu)->arch.schedule_tail)(vcpu))
 

xen/include/asm-x86/domain.h

@@ -395,7 +395,7 @@ struct arch_vcpu
 
     unsigned long      flags; /* TF_ */
 
-    void (*schedule_tail) (struct vcpu *);
+    void noreturn (*schedule_tail) (struct vcpu *);
 
     void (*ctxt_switch_from) (struct vcpu *);
     void (*ctxt_switch_to) (struct vcpu *);

xen/include/asm-x86/hvm/vmx/vmx.h

@@ -91,7 +91,7 @@ typedef enum {
 void vmx_asm_vmexit_handler(struct cpu_user_regs);
 void vmx_asm_do_vmentry(void);
 void vmx_intr_assist(void);
-void vmx_do_resume(struct vcpu *);
+void noreturn vmx_do_resume(struct vcpu *);
 void vmx_vlapic_msr_changed(struct vcpu *v);
 void vmx_realmode(struct cpu_user_regs *regs);
 void vmx_update_debug_state(struct vcpu *v);