[Bug c/52602] New: false compilation warning of uninitialized variable

[Bug c/52602] New: false compilation warning of uninitialized variable

[asmwarrior at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52602

             Bug #: 52602
           Summary: false compilation warning of uninitialized variable
    Classification: Unclassified
           Product: gcc
           Version: 4.6.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: asmwarrior@gmail.com


Hi, when building gdb, I found a false warning, the code is below:

static void
print_one_vtable (struct gdbarch *gdbarch, struct value *value,
          int max_voffset,
          struct value_print_options *opts)
{
  int i;
  struct type *type = check_typedef (value_type (value));
  struct value *vtable;
  CORE_ADDR vt_addr;

  vtable = gnuv3_get_vtable (gdbarch, type,
                 value_address (value)
                 + value_embedded_offset (value));
  vt_addr = value_address (value_field (vtable,
                    vtable_field_virtual_functions));

  printf_filtered (_("vtable for '%s' @ %s (subobject @ %s):\n"),
           TYPE_SAFE_NAME (type),
           paddress (gdbarch, vt_addr),
           paddress (gdbarch, (value_address (value)
                       + value_embedded_offset (value))));

  for (i = 0; i <= max_voffset; ++i)
    {
      struct value *vfn;
      CORE_ADDR addr;
      volatile struct gdb_exception ex;

      printf_filtered ("[%d]: ", i);

      vfn = value_subscript (value_field (vtable,
                      vtable_field_virtual_functions),
                 i);

      if (gdbarch_vtable_function_descriptors (gdbarch))
    vfn = value_addr (vfn);

      TRY_CATCH (ex, RETURN_MASK_ERROR)
    {
      addr = value_as_address (vfn);
    }
      if (ex.reason < 0)
    printf_filtered (_("<error: %s>"), ex.message);
      else
    print_function_pointer_address (gdbarch, addr, gdb_stdout,
                    opts->addressprint);
      printf_filtered ("\n");
    }
}

in GDB's source: gnu-v3-abi.c, the warning is:

.../../gdb/gdb/gnu-v3-abi.c: In function 'print_one_vtable.isra.2':
.../../gdb/gdb/gnu-v3-abi.c:892:33: error: 'addr' may be used uninitialized in
this function [-Werror=uninitialized]

and the bug is workaround by this patch:
http://sourceware.org/ml/gdb-cvs/2012-03/msg00203.html

Simply use: CORE_ADDR addr = 0;

Yuanhui Zhang

[Bug c/52602] false compilation warning of uninitialized variable

[asmwarrior at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52602

--- Comment #1 from asmwarrior <asmwarrior at gmail dot com> 2012-03-16 14:06:08 UTC ---
BTW: here is the discussion in gdb's patch mail list.
http://sourceware.org/ml/gdb-patches/2012-03/msg00585.html

[Bug c/52602] false compilation warning of uninitialized variable

[manu at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52602

Manuel López-Ibáñez <manu at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |WAITING
   Last reconfirmed|                            |2012-03-16
                 CC|                            |manu at gcc dot gnu.org
     Ever Confirmed|0                           |1

--- Comment #2 from Manuel López-Ibáñez <manu at gcc dot gnu.org> 2012-03-16 15:32:04 UTC ---
I know it is a pain in the ass to generate a (minimal) preprocessed testcase,
but this report is not very useful without it: http://gcc.gnu.org/bugs/

There are at least as many explanations for this as bugs are listed for
PR24639.