[PATCH] x86: mark compat hypercall regs clobbering for intended fall-through

[Jan Beulich <jbeulich@xxxxxxxx>]

Oddly enough in the original report Coverity only complained about the
native hypercall related switch() statements. Now that it has seen those
fixed, it complains about (only HVM) compat ones. Hence the CIDs below
are all for the HVM side of things, yet while at it take care of the PV
side as well.

Coverity-ID: 1487105, 1487106, 1487107, 1487108, 1487109.
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
I have to admit that I really have trouble spotting a pattern in what
Coverity spots or does not spot.

--- a/xen/arch/x86/hvm/hypercall.c
+++ b/xen/arch/x86/hvm/hypercall.c
@@ -292,11 +292,11 @@ int hvm_hypercall(struct cpu_user_regs *
         /* Deliberately corrupt parameter regs not used by this hypercall. */
         switch ( hypercall_args_table[eax].compat )
         {
-        case 0: ebx = 0xdeadf00d;
-        case 1: ecx = 0xdeadf00d;
-        case 2: edx = 0xdeadf00d;
-        case 3: esi = 0xdeadf00d;
-        case 4: edi = 0xdeadf00d;
+        case 0: ebx = 0xdeadf00d; fallthrough;
+        case 1: ecx = 0xdeadf00d; fallthrough;
+        case 2: edx = 0xdeadf00d; fallthrough;
+        case 3: esi = 0xdeadf00d; fallthrough;
+        case 4: edi = 0xdeadf00d; fallthrough;
         case 5: ebp = 0xdeadf00d;
         }
 #endif
@@ -312,11 +312,11 @@ int hvm_hypercall(struct cpu_user_regs *
             /* Deliberately corrupt parameter regs used by this hypercall. */
             switch ( hypercall_args_table[eax].compat )
             {
-            case 6: regs->rbp = 0xdeadf00d;
-            case 5: regs->rdi = 0xdeadf00d;
-            case 4: regs->rsi = 0xdeadf00d;
-            case 3: regs->rdx = 0xdeadf00d;
-            case 2: regs->rcx = 0xdeadf00d;
+            case 6: regs->rbp = 0xdeadf00d; fallthrough;
+            case 5: regs->rdi = 0xdeadf00d; fallthrough;
+            case 4: regs->rsi = 0xdeadf00d; fallthrough;
+            case 3: regs->rdx = 0xdeadf00d; fallthrough;
+            case 2: regs->rcx = 0xdeadf00d; fallthrough;
             case 1: regs->rbx = 0xdeadf00d;
             }
         }
--- a/xen/arch/x86/pv/hypercall.c
+++ b/xen/arch/x86/pv/hypercall.c
@@ -197,11 +197,11 @@ void pv_hypercall(struct cpu_user_regs *
         /* Deliberately corrupt parameter regs not used by this hypercall. */
         switch ( hypercall_args_table[eax].compat )
         {
-        case 0: ebx = 0xdeadf00d;
-        case 1: ecx = 0xdeadf00d;
-        case 2: edx = 0xdeadf00d;
-        case 3: esi = 0xdeadf00d;
-        case 4: edi = 0xdeadf00d;
+        case 0: ebx = 0xdeadf00d; fallthrough;
+        case 1: ecx = 0xdeadf00d; fallthrough;
+        case 2: edx = 0xdeadf00d; fallthrough;
+        case 3: esi = 0xdeadf00d; fallthrough;
+        case 4: edi = 0xdeadf00d; fallthrough;
         case 5: ebp = 0xdeadf00d;
         }
 #endif
@@ -223,11 +223,11 @@ void pv_hypercall(struct cpu_user_regs *
             /* Deliberately corrupt parameter regs used by this hypercall. */
             switch ( hypercall_args_table[eax].compat )
             {
-            case 6: regs->ebp = 0xdeadf00d;
-            case 5: regs->edi = 0xdeadf00d;
-            case 4: regs->esi = 0xdeadf00d;
-            case 3: regs->edx = 0xdeadf00d;
-            case 2: regs->ecx = 0xdeadf00d;
+            case 6: regs->ebp = 0xdeadf00d; fallthrough;
+            case 5: regs->edi = 0xdeadf00d; fallthrough;
+            case 4: regs->esi = 0xdeadf00d; fallthrough;
+            case 3: regs->edx = 0xdeadf00d; fallthrough;
+            case 2: regs->ecx = 0xdeadf00d; fallthrough;
             case 1: regs->ebx = 0xdeadf00d;
             }
         }