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printf from assembly

Offline Avi Levi over 9 years ago

Note: This was originally posted on 24th June 2011 at http://forums.arm.com

Hi,
I am trying to call printf from an assembly code but getting into some difficulties.
I found this post: How to Call a Function from ARM Assembler
However, when using the printf inside my code I get a linker error:

Error: L6238E: foo.o(.text) contains invalid call from '~PRES8' function to 'REQ8' function foobar

Searched for that as well, and found that I am calling a C function that requires 8-byte stack alignment
from an assembly code that does not preserve 8-bytes. (Hence the ~PRES8 and REQ8)
The article suggested that I should add the PRESERVE8 directive before my AREA directive:

add the PRESERVE8 directive to the top of each assembler file. For example, change:

AREA Init, CODE, READONLY

to:

PRESERVE8 AREA Init, CODE, READONLY

But when I do that I get an error that says:

Bad symbol 'AREA' not defined or external.

Can anyone please help me figure out how to do it right?

Thank you

Offline Etienne SOBOLE over 9 years ago

Note: This was originally posted on 24th June 2011 at http://forums.arm.com

what assembler do you use ?

gcc ?

if you use gcc, write your code in C and then compile it with
gcc -S myfile.c

that will make the assembly code (myfile.s) of your c program.
Then you'll be able to see how the printf work and the syntax will be correct.

Etienne
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Offline Scott Douglass over 9 years ago

Note: This was originally posted on 24th June 2011 at http://forums.arm.com

PRESERVE8 is a directive by itself and needs to be on a separate line:

PRESERVE8 AREA Init, CODE, READONLY ....

When you use the PRESERVE8 you are promising that any time you branch to an IMPORTED symbol you will have changed SP by a multiple of 8 (including 0). See also http://infocenter.ar...d/Cacehagj.html
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