Sharing header files between C and assembler

Applies to: ARM Developer Suite (ADS), RealView Developer Kit (RVDK) for OKI, RealView Developer Kit (RVDK) for ST, RealView Developer Kit for XScale (RVXDK), RealView Development Suite (RVDS), Software Development Toolkit (SDT)

To define, for example, constants in code, it is normal to use #define for C code and EQU for assembler code. You may have a project containing a mix of C and assembler code, where there are some constant definitions which are common to both the C and assembler code. In this case, it is useful to be able to create a list of common definitions that can be included into both C files and assembler files, to avoid maintaining two parallel lists.

Solutions for ADS 1.2, RVDS 2.x, RVDS 3.x and RVDS 4.0

In ADS 1.2 and later, you can include C style #include and #define directives directly in your assembler source. The assembler source can then be passed through the C compiler preprocessor, which outputs a "preprocessed" version of your assembler code, which can then be assembled in the normal way. Consider the following example:

----- ex.s -----
#include "my_header.h"

      AREA Example, CODE, READONLY
start
      MOV   r0, #ONE_CONSTANT
      ADD   r0, r0, r1
      MOV   pc,lr

      END
--- end ex.s ---

where my_header.h contains

#define ONE_CONSTANT 1

When ex.s is passed through the C preprocessor using the following command.

armcc -E ex.s > p_ex.s

The output file p_ex.s looks like this:

---- p_ex.s ----
#line 1 "ex.s"
#line 1 "my_header.h"

#line 2 "ex.s"

      AREA Example, CODE, READONLY
start
      MOV   r0, # 1
      ADD   r0, r0, r1
      MOV   pc,lr

      END
-- end p_ex.s --

p_ex.s can then be assembled in the normal way with armasm.

Unfortunately, the above cannot be done with ADS 1.1 or earlier because

when given a .s file, the compilers ignored -E, but invoked armasm directly instead
the assemblers did not understand #line.

Additional Information

In RVDS 4.0, you no longer need to invoke armcc to use C preprocessor macros in an assembly language source file or C preprocessor command-line options. To achieve this you can use the --cpreproc command-line option when invoking the assembler. The --cpreproc_opts command-line option can be used to pass additional options to the compiler. For example: armasm --cpreproc source.s. For more information on these options, please see the RVCT 4.0 Assembler Guide.

Solutions for ADS 1.1 (and earlier)

Two solutions for ADS 1.1 and earlier are given below:

The file include.zip contains two header files (stdcmac.h and stdsmac.h) which define various C and assembler macros.

If these are included in a project, a restricted C header (only containing #defines) can be included in assembler code. This solution could be extended to support other C directives such as #if, #ifdef, etc. An example header file options.h is also provided.

To include the file options.h in a C file use:
#include "stdcmac.h" #include "options.h"
To include the file options.h in an assembler file use:
INCLUDE stdsmac.h INCLUDE options.h
In your ADS or SDT installation you will find the file makelo.c in the Angel / Source directories. This code includes various C headers and then produces text output containing appropriate assembler definitions to match the C defines. Although this code is application specific (i.e. not intended for general use), you may find it helpful as a rough outline if you wish to implement your solution this way.

Attachments: include.zip

Article last edited on: 2009-07-08 11:47:41

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