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SW4STM32 and SW4Linux fully supports the STM32MP1 asymmetric multicore Cortex/A7+M4 MPUs

   With System Workbench for Linux, Embedded Linux on the STM32MP1 family of MPUs from ST was never as simple to build and maintain, even for newcomers in the Linux world.
And, if you install System Workbench for Linux in System Workbench for STM32 you can seamlessly develop and debug asymmetric applications running partly on Linux, partly on the Cortex-M4.
You can get more information from the ac6-tools website and download two short videos (registration required) highlighting:

System Workbench for STM32

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You are viewing a reply to generating position independent code problem on STM32F4  

generating position independent code problem on STM32F4

Posted by SyUm75 on 2017-11-13 10:13

Dear Bernard,

thanks for your quick reply, I did not see the post (did not receive the email).

I have in my project a part I’d like to compile with the fPIC option.
I made a call to a test_function from a function in the code compiled with the fPIC option. The test_function also resides in a file compiled with the fPIC option.

Here is an excerpt of the generated assembly (copied from the disassembly view in the eclipse plugin) when using -fPIC option:

135 int ret = test_function(4);
08050802: movs r0, #4
08050804: bl 0x8050964

It appears the generated fPIC code does NOT use relative call inside the fPIC compiled module.

But maybe I have been tricked by the assembly display or do I miss something?

Thanks for your help,
Best regards,
Sylvain

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Posted by dautrevaux on 2017-11-13 18:38 France

Hi Sylvain,

As I said in my previous post, BL is ALWAYS using relative addressing; to use absolute adressing you would have to use code like this:
LD R12,=test_function
BLX R12
where the first instruction will in turn be displayed in disassembly as two instruction: a MOVW #xxxx to load the 16 lsb (setting the msb to 0) and a MOVT #xxxx to load the 16 msb

Thus the code you show is indeed using relative addressing, so is perfectly valid in PIC mode.

Bernard (Ac6)

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