Re: question about __builtin___memcpy_chk and friends

[Siddhesh Poyarekar]

On 2025-12-16 09:31, Siddhesh Poyarekar wrote:
Aha, ok!  It looks like test2_sub needs to be broken up then, to have 
each of those tests run independently.  That way the compiler won't have 
a chance to leak the result of one test into the ones that follow.

Something like:

__attribute__((noinline))
test2_sub_1 (...)
{
   if (__builtin_memcpy (buf3, "ABCDEF", 6) != (char *) buf1
       || memcmp (buf1, "ABCDEFghijklmnopq\0", 19))
     abort ();
}

test2_sub ()
{
...
   test2_sub_1 (buf3, buf4, buf6, n);
...
}

and so on.  Basically all of the tests with buf3 based expressions as 
the destination need their own noinline function.

Alternatively, maybe this (attached) could work too, to reduce the 
amount of churn in the test?  Basically compare with a volatile b1 
instead of buf1 to prevent the comparisons from resulting in a proof of 
equivalence?

Siddiff --git a/gcc/testsuite/gcc.c-torture/execute/builtins/memcpy-chk.c 
b/gcc/testsuite/gcc.c-torture/execute/builtins/memcpy-chk.c
index 5b245e58e22..7904878a47f 100644
--- a/gcc/testsuite/gcc.c-torture/execute/builtins/memcpy-chk.c
+++ b/gcc/testsuite/gcc.c-torture/execute/builtins/memcpy-chk.c
@@ -88,6 +88,7 @@ __attribute__((noinline))
 test2_sub (long *buf3, char *buf4, char *buf6, int n)
 {
   int i = 0;
+  volatile char *b1 = buf1;
 
   /* All the memcpy/__builtin_memcpy/__builtin___memcpy_chk
      calls in this routine are either fixed length, or have
@@ -104,22 +105,22 @@ test2_sub (long *buf3, char *buf4, char *buf6, int n)
       || memcmp (buf1, "abcdefghijklmnopq\0", 19))
     abort ();
 
-  if (__builtin_memcpy (buf3, "ABCDEF", 6) != (char *) buf1
-      || memcmp (buf1, "ABCDEFghijklmnopq\0", 19))
+  if (__builtin_memcpy (buf3, "ABCDEF", 6) != (char *) b1
+      || memcmp (b1, "ABCDEFghijklmnopq\0", 19))
     abort ();
 
-  if (__builtin_memcpy (buf3, "a", 1) != (char *) buf1
-      || memcmp (buf1, "aBCDEFghijklmnopq\0", 19))
+  if (__builtin_memcpy (buf3, "a", 1) != (char *) b1
+      || memcmp (b1, "aBCDEFghijklmnopq\0", 19))
     abort ();
 
-  if (memcpy ((char *) buf3 + 2, "bcd" + ++i, 2) != (char *) buf1 + 2
-      || memcmp (buf1, "aBcdEFghijklmnopq\0", 19)
+  if (memcpy ((char *) buf3 + 2, "bcd" + ++i, 2) != (char *) b1 + 2
+      || memcmp (b1, "aBcdEFghijklmnopq\0", 19)
       || i != 1)
     abort ();
 
   /* These should probably be handled by move_by_pieces on most arches.  */
-  if (memcpy ((char *) buf3 + 4, buf5, 6) != (char *) buf1 + 4
-      || memcmp (buf1, "aBcdRSTUVWklmnopq\0", 19))
+  if (memcpy ((char *) buf3 + 4, buf5, 6) != (char *) b1 + 4
+      || memcmp (b1, "aBcdRSTUVWklmnopq\0", 19))
     abort ();
 
   if (__builtin_memcpy ((char *) buf1 + ++i + 8, (char *) buf5 + 1, 1)
@@ -128,16 +129,16 @@ test2_sub (long *buf3, char *buf4, char *buf6, int n)
       || i != 2)
     abort ();
 
-  if (memcpy ((char *) buf3 + 14, buf6, 2) != (char *) buf1 + 14
-      || memcmp (buf1, "aBcdRSTUVWSlmnrsq\0", 19))
+  if (memcpy ((char *) buf3 + 14, buf6, 2) != (char *) b1 + 14
+      || memcmp (b1, "aBcdRSTUVWSlmnrsq\0", 19))
     abort ();
 
-  if (memcpy (buf3, buf5, 8) != (char *) buf1
-      || memcmp (buf1, "RSTUVWXYVWSlmnrsq\0", 19))
+  if (memcpy (buf3, buf5, 8) != (char *) b1
+      || memcmp (b1, "RSTUVWXYVWSlmnrsq\0", 19))
     abort ();
 
-  if (memcpy (buf3, buf5, 17) != (char *) buf1
-      || memcmp (buf1, "RSTUVWXYZ01234567\0", 19))
+  if (memcpy (buf3, buf5, 17) != (char *) b1
+      || memcmp (b1, "RSTUVWXYZ01234567\0", 19))
     abort ();
 
   __builtin_memcpy (buf3, "aBcdEFghijklmnopq\0", 19);