[Bug 280146] Incorrect operation of strcpy/strncpy (libc.so.7)

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=280146

            Bug ID: 280146
           Summary: Incorrect operation of strcpy/strncpy (libc.so.7)
           Product: Base System
           Version: 14.1-RELEASE
          Hardware: amd64
                OS: Any
            Status: New
          Severity: Affects Many People
          Priority: ---
         Component: bin
          Assignee: bugs@FreeBSD.org
          Reporter: work+freebsd@vvv.kiev.ua

Starting from 14.1 strcpy/strncpy functions don't work correctly in some cases.

The following simple program prints wrong result with strcpy:

#include <stdio.h>
#include <string.h>

int main(void)
{
    char str[1024] = "0a1b2c3d4e5f6g7h8i9j0k1l2m3n4o5p6q7r8s9t0u1v2w3x";
    printf("%s\n", str);
    strcpy(str, str + 1);
    printf("%s\n", str);
    return 0;
}

Actual result:
0a1b2c3d4e5f6g7h8i9j0k1l2m3n4o5p6q7r8s9t0u1v2w3x
a1b2c3d4e5f6g7h8i9j0k1l2m3n4o5p67r8s9t0u1v2w3xx

Expected result:
0a1b2c3d4e5f6g7h8i9j0k1l2m3n4o5p6q7r8s9t0u1v2w3x
a1b2c3d4e5f6g7h8i9j0k1l2m3n4o5p6q7r8s9t0u1v2w3x


And with strncpy:

#include <stdio.h>
#include <string.h>

int main(void)
{
    char str[1024] = "0a1b2c3d4e5f6g7h8i9j0k1l2m3n4o5p6q7r8s9t0u1v2w3x";
    printf("%s\n", str);
    strncpy(str, str + 1, strlen(str));
    printf("%s\n", str);
    return 0;
}

Actual result:
0a1b2c3d4e5f6g7h8i9j0k1l2m3n4o5p6q7r8s9t0u1v2w3x
a1b2c3d4e5f6g7h8i9j0k1l2m3n4o5p

Expected result:
0a1b2c3d4e5f6g7h8i9j0k1l2m3n4o5p6q7r8s9t0u1v2w3x
a1b2c3d4e5f6g7h8i9j0k1l2m3n4o5p6q7r8s9t0u1v2w3x


Both programs work correctly in 13.3, 14.0 and older.

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