PIE/PIC issue ...w.r.t linker variable

[Kyrill Tkachov]

On 12/02/16 09:58, Umesh Kalappa wrote:
> Hi Kyrill ,
> Thank you for the info ,before i file a bug ,need to confirm its a bug or not .

I'm not familiar with linker scripts and the details of -fpie,
so unfortunately I can't judge.

Do file a bug report.
If it is not a bug, it will be closed as such by someone who does
the analysis.

Kyrill

> Thank you
> ~Umesh
>
> On Fri, Feb 12, 2016 at 3:00 PM, Kyrill Tkachov
> <kyrylo.tkachov@foss.arm.com> wrote:
>> Hi,
>>
>>
>> On 12/02/16 09:19, Umesh Kalappa wrote:
>>> Hi Guys ,
>>>
>>> we  do have a issue with below code ,When we enabled the pie (-fpie/pie)
>>> option
>>>    i.e
>>>
>>> main.c
>>> extern int *my_ptr ;
>>>
>>> int main()
>>> {
>>>      return *my_ptr;
>>> }
>>>
>>> foo.s
>>>    .syntax unified
>>>    .cpu cortex-m0
>>>    .fpu softvfp
>>>     .thumb
>>>     .global my_ptr
>>>      .global my_var
>>>       .data
>>>       .align  2
>>>      .type   my_ptr, %object
>>>      .size   my_ptr, 4
>>> my_ptr:
>>>     .word   my_var   //where my_var is the linker variable
>>>
>>> custom.ld  (linker script)
>>> /* Set stack top to end of RAM, and stack limit move down by
>>>       190      * size of stack_dummy section */
>>>       191     my_var = 20;
>>>       192     __StackTop = ORIGIN(RAM) + LENGTH(RAM);
>>>       193     __StackLimit = __StackTop - SIZEOF(.stack_dummy);
>>>       194     PROVIDE(__stack = __StackTop);
>>>
>>>
>>> command used
>>>
>>>         3  arm-none-eabi-gcc -c -fPIC main.c -mthumb -mcpu=cortex-m0
>>>         4
>>>         5 arm-none-eabi-gcc -c -fPIC foo.S -mthumb -mcpu=cortex-m0
>>>         6 arm-none-eabi-gcc -c -fPIC
>>>
>>> /home/egoumal/Downloads/gcc-arm-none-eabi-5_2-2015q4/share/gcc-arm-none-eabi/samples/startup/startu
>>>          p_ARMCM0.S -mthumb -mcpu=cortex-m0 -D__STARTUP_CLEAR_BSS
>>> -D__START=main
>>>         7
>>>         8 arm-none-eabi-ld -pie main.o  foo.o startup_ARMCM0.o -L.
>>> -L/home/egoumal/Downloads/gcc-arm-none-eabi-5_2-2015q4/share/gcc-ar
>>>       m-none-eabi/samples/ldscripts -T nokeep.ld -Map=test.map -o test
>>>
>>> we expect my_ptr value to be 20 ,but we do see the value 0 and without
>>> pie option ,the my_ptr has the value 20 .
>>>
>>> do we missing something here  or value 0 expected (which is incorrect)
>>
>> note that gcc-bugs is the list where the automatic bug tracker sends all the
>> emails
>> logging almost all activity, so your email would be lost there...
>> Please file a bug report in bugzilla according to https://gcc.gnu.org/bugs/
>>
>> Thanks,
>> Kyrill
>>
>>
>>> Thank you and appreciate any lights on this
>>> ~Umesh
>>>