Created attachment 235429 [details] [review]
Patch file to fix the issue

The function print_long_long always prints a long long number as signed (when conversion is "u", e.g. %llu in printf). So printing a number with the MSB set results in a negative output.

E.g.: g_snprintf(buf, sizeof(buf), "%llu", 0xffffffffffffffffLL); 

will print "-1" (instead of 18446744073709551615).

The problem seems to be, that the function always checks whether the number is negative, unless the conversion is o,x or X. 

    default:
      base = 10;
      digits = lower;
      negative = (long long)number < 0;
      if (negative)
        number = -((long long)number);
      break;

Adding a special case for 'u' would of course fix this (I think):

    case 'u':
      base = 10;
      digits = lower;
      negative = FALSE;
      break;


I noticed this in glib 2.22.5 but it looks like this is still the same in the latest version? Of course this function is only used when glib is compiled with --enable-included-printf or the system does not provide a proper printf function itself.