syscall_steal: rename sys_call_table to fix compile error

sys_call_table is already declared in arch/x86/include/asm/syscall.h but of
cource not exported by the kernel.
before this commit, gcc complains as follows:
/usr/src/linux-headers-6.1.0-16-common/arch/x86/include/asm/syscall.h:21:29:
note: previous declaration of 'sys_call_table' with type 'long int (*
const[])(const struct pt_regs *)'
   21 | extern const sys_call_ptr_t sys_call_table[];

examples/syscall_steal.c

@@ -61,7 +61,7 @@ module_param(sym, ulong, 0644);
 
 #endif /* Version < v5.7 */
 
-static unsigned long **sys_call_table;
+static unsigned long **sys_call_table_stolen;
 
 /* UID we want to spy on - will be filled from the command line. */
 static uid_t uid = -1;
@@ -208,16 +208,16 @@ static void disable_write_protection(void)
 
 static int __init syscall_steal_start(void)
 {
-    if (!(sys_call_table = acquire_sys_call_table()))
+    if (!(sys_call_table_stolen = acquire_sys_call_table()))
         return -1;
 
     disable_write_protection();
 
     /* keep track of the original open function */
-    original_call = (void *)sys_call_table[__NR_openat];
+    original_call = (void *)sys_call_table_stolen[__NR_openat];
 
     /* use our openat function instead */
-    sys_call_table[__NR_openat] = (unsigned long *)our_sys_openat;
+    sys_call_table_stolen[__NR_openat] = (unsigned long *)our_sys_openat;
 
     enable_write_protection();
 
@@ -228,11 +228,11 @@ static int __init syscall_steal_start(void)
 
 static void __exit syscall_steal_end(void)
 {
-    if (!sys_call_table)
+    if (!sys_call_table_stolen)
         return;
 
     /* Return the system call back to normal */
-    if (sys_call_table[__NR_openat] != (unsigned long *)our_sys_openat) {
+    if (sys_call_table_stolen[__NR_openat] != (unsigned long *)our_sys_openat) {
         pr_alert("Somebody else also played with the ");
         pr_alert("open system call\n");
         pr_alert("The system may be left in ");
@@ -240,7 +240,7 @@ static void __exit syscall_steal_end(void)
     }
 
     disable_write_protection();
-    sys_call_table[__NR_openat] = (unsigned long *)original_call;
+    sys_call_table_stolen[__NR_openat] = (unsigned long *)original_call;
     enable_write_protection();
 
     msleep(2000);