Multi‐file compilation

Introduction

The IAR C/C++ Compiler offers the possibility for multi-file compiling to gather a file set into a single compilation unit. From the compiler's perspective, the file set must be passed as additional parameters from a single invocation, with the --mfc option:

iccarm file1.c file2.c file3.c --mfc ...

As per CMake 3.28, target_sources() doesn't provide a clear way for specifying file sets for such purpose.

Applies to

• CMake targets using 2 or more source files.

Solutions

Consider one of the following approaches for when building a target using multi-file compilation:

Approach #1 - Include *.c source files into a single compilation unit

Changing the source code to include the file set from a single compilation unit wil effectively mimic the effect provided by --mfc:

/* File: file1.c */

#include "file2.c"
#include "file3.c"
/* ... */

void main() { 
/* ... */

Approach #2 - Trick CMake by passing the file set as target_compile_options()

Sometimes changing the sources might be cumbersome depending on how large the project was partitioned. A workaround for using --mfc from a CMake project could be:

cmake_minimum_required(VERSION 3.20)

project(MyProject)

add_executable(MyProject)

target_sources(MyProject PRIVATE file1.c)

set(MFC_FILES ${CMAKE_CURRENT_SOURCE_DIR}/file2.c ${CMAKE_CURRENT_SOURCE_DIR}/file3.c)

target_compile_options(MyProject PRIVATE ${MFC_FILES} --mfc --discard_unused_publics)

target_link_options(MyProject PRIVATE --semihosting)

where the output from cmake --build . --clean-first --verbose would be:

[1/2] /opt/iarsystems/bxarm/arm/bin/iccarm --silent /myproject/file1.c /myproject/file2.c /myproject/file3.c --mfc --discard_unused_publics --dependencies=ns CMakeFiles/myproject.dir/file1.o.d -o CMakeFiles/myproject.dir/file1.o
[2/2] : && /opt/iarsystems/bxarm/arm/bin/ilinkarm CMakeFiles/myproject.dir/file1.o --silent --semihosting -o MyProject.elf && :

Tip

According to the User Guide, the option --discard_unused_publics might be helpful in scenarios where --mfc is used within a project-wide scope, where the compiler can have full visibility of the source code from a single compilation unit.