xen/x86: add missing noreturn attributes

The marked functions never return to their caller, but lack the
`noreturn' attribute.

Functions that never return should be declared with a `noreturn'
attribute.

The lack of `noreturn' causes a violation of MISRA C Rule 17.11 (not
currently accepted in Xen), and also Rule 2.1: "A project shall not
contain unreachable code". Depending on the compiler used and the
compiler optimization used, the lack of `noreturn' might lead to the
presence of unreachable code.

The usage of the noreturn attribute together with asmlinkage is only for
the benefit of the static analysis tools.

No functional change.

Signed-off-by: Nicola Vetrini <nicola.vetrini@bugseng.com>
Signed-off-by: Victor Lira <victorm.lira@amd.com>
[stefano: improve commit message]
Signed-off-by: Stefano Stabellini <stefano.stabellini@amd.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Acked-by: Roger Pau Monné <roger.pau@citrix.com>

xen/arch/x86/cpu/mcheck/mce.c

@@ -79,7 +79,8 @@ static int __init cf_check mce_set_verbosity(const char *str)
 custom_param("mce_verbosity", mce_set_verbosity);
 
 /* Handle unconfigured int18 (should never happen) */
-static void cf_check unexpected_machine_check(const struct cpu_user_regs *regs)
+static void noreturn cf_check
+unexpected_machine_check(const struct cpu_user_regs *regs)
 {
     console_force_unlock();
     printk("Unexpected Machine Check Exception\n");

xen/arch/x86/efi/efi-boot.h

@@ -769,7 +769,7 @@ static void __init efi_arch_blexit(void)
         efi_bs->FreePages(ucode.addr, PFN_UP(ucode.size));
 }
 
-static void __init efi_arch_halt(void)
+static void noreturn __init efi_arch_halt(void)
 {
     local_irq_disable();
     for ( ; ; )

xen/arch/x86/smp.c

@@ -343,7 +343,7 @@ void __stop_this_cpu(void)
     cpumask_clear_cpu(smp_processor_id(), &cpu_online_map);
 }
 
-static void cf_check stop_this_cpu(void *dummy)
+static void noreturn cf_check stop_this_cpu(void *dummy)
 {
     const bool *stop_aps = dummy;
 

xen/arch/x86/traps.c

@@ -805,7 +805,7 @@ void fatal_trap(const struct cpu_user_regs *regs, bool show_remote)
           (regs->eflags & X86_EFLAGS_IF) ? "" : " IN INTERRUPT CONTEXT");
 }
 
-void asmlinkage do_unhandled_trap(struct cpu_user_regs *regs)
+void asmlinkage noreturn do_unhandled_trap(struct cpu_user_regs *regs)
 {
     fatal_trap(regs, false);
 }

xen/arch/x86/x86_64/traps.c

@@ -293,7 +293,7 @@ void show_page_walk(unsigned long addr)
            l1_table_offset(addr), l1e_get_intpte(l1e), pfn);
 }
 
-void asmlinkage do_double_fault(struct cpu_user_regs *regs)
+void asmlinkage noreturn do_double_fault(struct cpu_user_regs *regs)
 {
     unsigned int cpu;
     struct extra_state state;