Re: [PATCH 01/14] Prepare vfprintf to use __printf_fp/__printf_fphex with float128 arg

["Gabriel F. T. Gomes" <gabriel at inconstante dot eti dot br>]

On Tue, 18 Dec 2018, Florian Weimer wrote:

>* Gabriel F. T. Gomes:
>>
>> @@ -1887,7 +1930,12 @@ printf_positional (FILE *s, const CHAR_T *format, int readonly_format,
>>  	      (args_value[cnt].pa_user, ap_savep);
>>  	  }
>>  	else
>> -	  args_value[cnt].pa_long_double = 0.0;
>> +	  {
>> +	    args_value[cnt].pa_long_double = 0.0;
>> +#if __HAVE_FLOAT128_UNLIKE_LDBL
>> +	    args_value[cnt].pa_float128 = 0;
>> +#endif
>> +	  }  
>
>This bit doesn't look right to me because args_value[cnt] is a union.
>You need to assign to the right member, or perhaps zero-initialize using
>memset.

Hmm, the original code doesn't seem to be dealing with anything particular
to the long double type.  It seems that assigning to .pa_long_double,
rather than to other members, was an arbitrary decision.  Do you know
why .pa_long_double was chosen?

So, if this code is just zero-initializing the memory, do you think I
should zero-initialize the whole of args_value/argsbuf.data when it gets
expanded (see below)?  Then I could remove the else block entirely.

Like this:

diff --git a/stdio-common/vfprintf-internal.c b/stdio-common/vfprintf-internal.c
index 61769e0ce1..17f1bae796 100644
--- a/stdio-common/vfprintf-internal.c
+++ b/stdio-common/vfprintf-internal.c
@@ -1789,10 +1789,11 @@ printf_positional (FILE *s, const CHAR_T *format, int readonly_format,
     if (!scratch_buffer_set_array_size (&argsbuf, nargs, bytes_per_arg))
       {
        done = -1;
        goto all_done;
       }
+    memset (argsbuf.data, 0, argsbuf.size);
     args_value = argsbuf.data;
     /* Set up the remaining two arrays to each point past the end of
        the prior array, since space for all three has been allocated
        now.  */
     args_size = &args_value[nargs].pa_int;
@@ -1884,12 +1885,10 @@ printf_positional (FILE *s, const CHAR_T *format, int readonly_format,
          {
            args_value[cnt].pa_user = alloca (args_size[cnt]);
            (*__printf_va_arg_table[args_type[cnt] - PA_LAST])
              (args_value[cnt].pa_user, ap_savep);
          }
-       else
-         args_value[cnt].pa_long_double = 0.0;
        break;
       case -1:
        /* Error case.  Not all parameters appear in N$ format
           strings.  We have no way to determine their type.  */
        assert ((mode_flags & PRINTF_FORTIFY) != 0);