Make mmap livepatchable using glibc's syscall

This patch addresses the mmap livepatching issue[1]
by invoking mmap system call through glibc's syscall
interface. Hence, enabling livepatching on mmap
library function.

This change shifts the existing limitation from
mmap to syscall of glibc. Excluding syscall from
livepatchable set is acceptable due to its
minimal design.

[1] #239

Signed-off-by: Abhishek Dubey <adubey@linux.ibm.com>

Author: Abhishek Dubey

Diff for: lib/arch/powerpc64le/patch.c

@@ -25,6 +25,7 @@
 #include <unistd.h>
 #include <pthread.h>
 #include <sys/mman.h>
+#include <sys/syscall.h>
 
 #include <stddef.h>
 #include <string.h>
@@ -271,7 +272,7 @@ void *ulp_stack_helper(void)
   void *old = (void *)ulp_stack[ULP_STACK_PTR];
 
   /* Allocate buffer for our stack.  */
-  void *new = mmap(NULL, ulp_stack[ULP_STACK_REAL_SIZE],
+  void *new = (void*) syscall(SYS_mmap, NULL, ulp_stack[ULP_STACK_REAL_SIZE],
                    PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
 
   if (new == (void *) -1) {