tests/tcg: take into account expected clashes pauth-4

Pointer authentication isn't perfect so measure the percentage of
failed checks. As we want to vary the pointer we work through a bunch
of different addresses.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Robert Foley <robert.foley@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20200225124710.14152-20-alex.bennee@linaro.org>

tests/tcg/aarch64/pauth-4.c

@@ -1,17 +1,30 @@
 #include <stdint.h>
 #include <assert.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#define TESTS 1000
 
 int main()
 {
-  uintptr_t x, y;
+    int i, count = 0;
+    float perc;
+    void *base = malloc(TESTS);
 
-  asm("mov %0, lr\n\t"
+    for (i = 0; i < TESTS; i++) {
+        uintptr_t in, x, y;
+
+        in = i + (uintptr_t) base;
+
+        asm("mov %0, %[in]\n\t"
             "pacia %0, sp\n\t"        /* sigill if pauth not supported */
             "eor %0, %0, #4\n\t"      /* corrupt single bit */
             "mov %1, %0\n\t"
             "autia %1, sp\n\t"        /* validate corrupted pointer */
             "xpaci %0\n\t"            /* strip pac from corrupted pointer */
-      : "=r"(x), "=r"(y));
+            : /* out */ "=r"(x), "=r"(y)
+            : /* in */ [in] "r" (in)
+            : /* clobbers */);
 
         /*
          * Once stripped, the corrupted pointer is of the form 0x0000...wxyz.
@@ -20,6 +33,13 @@ int main()
          * extracting explicit bits from the top, because the location of the
          * error code "e" depends on the configuration of virtual memory.
          */
-  assert(x != y);
+        if (x != y) {
+            count++;
+        }
+
+    }
+    perc = (float) count / (float) TESTS;
+    printf("Checks Passed: %0.2f%%", perc * 100.0);
+    assert(perc > 0.95);
     return 0;
 }