Epiphany port - printf prints wrong values of vars argument list

[Hesham Moustafa]

Hi Gedare,

Thanks for your reply.

On Thu, Dec 4, 2014 at 6:51 PM, Gedare Bloom <gedare at rtems.org> wrote:
> With only a string, printf goes to puts. So it sounds like the printf
> with arguments is broken. There is a slew of code hiding underneath
> the printf interface, and tiny problems in register ABI and memory
> layout easily render printf broken. I would start by modifying hello
> world to print a formatted string, so that you isolate from any
> problems due to timers / interrupts. You can then step in printf and
> see what the register arguments are, and that they correspond to what
> you might expect. Stepping through printf is a painful, tedious
> exercise, but hopefully you can find where things are going wrong. You
> might also try to binary search through the call trace, by generating
> the stack trace and then checking along it to see what the function
> arguments are, and how they track back to the high-level printf()
> call.
>
I did the exact same debugging technique you said here. I think it's
something related to a bug that I fixed related to GCC alignment that
broke down the ABI. I can't revert back the gcc code, because this
will cause unalignment exception (during initializing data structures)
and even hello world won't work. I am discussing this issue with
Epiphany folks currently.
> -Gedare
>
> On Thu, Dec 4, 2014 at 12:46 PM, Hesham Moustafa
> <heshamelmatary at gmail.com> wrote:
>> Hi,
>>
>> I have a problem with getting printf working correctly. printf is
>> working totally fine with just one string argument (hello world for
>> example), however when printf is passed some variable arguments, it
>> totally prints some garbage strings. Printing time function (in
>> ticker) is an example for this, even a simple printf("x = %d", x);
>> where x is defined before to an arbitrary value, output a wrong value
>> for x, although it output the "x =" string right. I made sure that the
>> address of x (or time structure content in case of ticker) is not
>> overwritten, and from GDB, breaking at this and printing x or
>> time->seconds for example gets me the right expected values. I think
>> the problem is with var arg list, any ideas?
>>
>> Thanks,
>> Hesham
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