[Valgrind-users] memcheck 2.0.0 complains about init bit [false positive error report]

[John R. <jr...@Bi...>]

Valgrind 2.0.0 (memcheck) complains about a bit that is not uninitialized.

-----jfrtest1.c
int
test1()
{
          unsigned x;  /* uninitialized */
          x &= 0x0000000c;  /* possible 0, 4, 8, 12 */
          if (2 & (x % 15)) { /* memcheck complains but should not */
                  return 1;
          }
          else {
                  return 0;
          }
}

int
main()
{
          return test1();
}
-----end jfrtest1.c

$ gcc -g -o jfrtest1 jfrtest1.c
$ valgrind ./jfrtest1
==7084== Memcheck, a.k.a. Valgrind, a memory error detector for x86-linux.
==7084== Copyright (C) 2002-2003, and GNU GPL'd, by Julian Seward.
==7084== Using valgrind-2.0.0, a program supervision framework for x86-linux.
==7084== Copyright (C) 2000-2003, and GNU GPL'd, by Julian Seward.
==7084== Estimated CPU clock rate is 1619 MHz
==7084== For more details, rerun with: -v
==7084==
==7084== Conditional jump or move depends on uninitialised value(s)
==7084==    at 0x8048318: test1 (jfrtest1.c:6)
==7084==    by 0x8048343: main (jfrtest1.c:17)
==7084==    by 0x40247AB6: __libc_start_main (in /lib/libc-2.3.2.so)
==7084==    by 0x8048264: ??? (start.S:81)

$ gdb ./jfrtest1   ## generated assembly code looks OK
(gdb) x/23i test1
0x80482f4 <test1>:      push   %ebp
0x80482f5 <test1+1>:    mov    %esp,%ebp
0x80482f7 <test1+3>:    sub    $0xc,%esp
0x80482fa <test1+6>:    lea    0xfffffffc(%ebp),%eax
0x80482fd <test1+9>:    andl   $0xc,(%eax)
0x8048300 <test1+12>:   mov    0xfffffffc(%ebp),%edx
0x8048303 <test1+15>:   mov    %edx,%eax
0x8048305 <test1+17>:   mov    $0xf,%ecx
0x804830a <test1+22>:   mov    $0x0,%edx
0x804830f <test1+27>:   div    %ecx
0x8048311 <test1+29>:   mov    %edx,%eax
0x8048313 <test1+31>:   and    $0x2,%eax
0x8048316 <test1+34>:   test   %eax,%eax
0x8048318 <test1+36>:   je     0x8048323 <test1+47>   ## complaint here
0x804831a <test1+38>:   movl   $0x1,0xfffffff8(%ebp)
0x8048321 <test1+45>:   jmp    0x804832a <test1+54>
0x8048323 <test1+47>:   movl   $0x0,0xfffffff8(%ebp)
0x804832a <test1+54>:   mov    0xfffffff8(%ebp),%eax
0x804832d <test1+57>:   leave
0x804832e <test1+58>:   ret


gcc version 3.2.2 20030222 (Red Hat Linux 3.2.2-5)
glibc-2.3.2-27.9.6
System is Red Hat 9: 2.4.20-20.9.

-- 
John Reiser, jr...@Bi...