[MSan] fix process_vm_readv test: Exit silently if syscall is not implemeted

[mohit.bhakkad]

Summary

In older kernel versions, process_vm_readv() is not implemented.

[eugenis]

LGTM

compiler-rt/trunk/test/msan/Linux/process_vm_readv.cc

 // RUN: %clangxx_msan -std=c++11 -O0 %s -o %t && %run %t
 // RUN: %clangxx_msan -std=c++11 -O0 %s -o %t -DPOSITIVE && not %run %t |& FileCheck %s
 
 #include <assert.h>
 #include <dlfcn.h>
 #include <sanitizer/msan_interface.h>
 #include <stdio.h>
 #include <string.h>
 #include <sys/types.h>
 #include <sys/uio.h>
 #include <unistd.h>
+#include <errno.h>
 
 typedef ssize_t (*process_vm_readwritev_fn)(pid_t, const iovec *, unsigned long,
                                             const iovec *, unsigned long,
                                             unsigned long);
 
-int main(void) {
-  // This requires glibc 2.15.
-  process_vm_readwritev_fn libc_process_vm_readv =
-      (process_vm_readwritev_fn)dlsym(RTLD_NEXT, "process_vm_readv");
-  if (!libc_process_vm_readv) {
 // Exit with success, emulating the expected output.
+int exit_dummy()
+{
 #ifdef POSITIVE
-    printf("process_vm_readv not found!\n");
+    printf("process_vm_readv not found or not implemented!\n");
     printf(
         "WARNING: MemorySanitizer: use-of-uninitialized-value (not really)\n");
     return 1;
 #else
     return 0;
 #endif
-  }
 
+int main(void) {
+  // This requires glibc 2.15.
+  process_vm_readwritev_fn libc_process_vm_readv =
+      (process_vm_readwritev_fn)dlsym(RTLD_NEXT, "process_vm_readv");
+  if (!libc_process_vm_readv)
+    return exit_dummy();
+
   process_vm_readwritev_fn process_vm_readv =
       (process_vm_readwritev_fn)dlsym(RTLD_DEFAULT, "process_vm_readv");
   process_vm_readwritev_fn process_vm_writev =
       (process_vm_readwritev_fn)dlsym(RTLD_DEFAULT, "process_vm_writev");
 
   char a[100];
   memset(a, 0xab, 100);
 
   char b[100];
   iovec iov_a[] = {{(void *)a, 20}, (void *)(a + 50), 10};
   iovec iov_b[] = {{(void *)(b + 10), 10}, (void *)(b + 30), 20};
 
   __msan_poison(&b, sizeof(b));
   ssize_t res = process_vm_readv(getpid(), iov_b, 2, iov_a, 2, 0);
+  if (errno == ENOSYS) // Function not implemented 
+    return exit_dummy();
+
   assert(res == 30);
   __msan_check_mem_is_initialized(b + 10, 10);
   __msan_check_mem_is_initialized(b + 30, 20);
   assert(__msan_test_shadow(b + 9, 1) == 0);
   assert(__msan_test_shadow(b + 20, 1) == 0);
   assert(__msan_test_shadow(b + 29, 1) == 0);
   assert(__msan_test_shadow(b + 50, 1) == 0);