C++ support

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Revision as of 03:45, 6 December 2018 by Claudio (talk | contribs) (STL support)
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Introduction

Despite the fact that ERIKA is implemented using the C and the Assembly programming languages, it has experimental support for linking applications implemented using the C++ language.

Basic support

The .cpp file extension is automatically recognized and handled by the Makefiles.

Put in the OIL file the following information:

  CFLAGS = "-std=c++11";
  CFLAGS = "-fno-exceptions";
  CFLAGS = "-mstrict-align";

Moreover, embed through the following braces any C symbol that must be linked to the application (e.g. idle_hook, tasks, etc.)

  extern "C"{
     //...
  }

The main function can be left outside the braces.

This must be done also for external libraries. In case of Jailhouse, for example, the inmate library must be modified as shown here.

This is the basic list of the supported features:

  • Normal classes
  • Template metaprogramming
  • C++11: lambda expressions, type deduction (i.e. auto)

STL support

In addition to the steps described in the previous section, if you also want to support the STL features provided by the bare-metal newlib toolchain (e.g., the one provided by Linaro's bare-metal gcc toolchain for ARM), you have to modify the linker script to set the end symbol:

  .data   : {
    *(.data)
  }
  
  . = ALIGN(8);
  /* "end" is used by newlib's syscalls */
  PROVIDE(end = .);
  
  . = ALIGN(16);
  stack_bottom = .;
  . = ALIGN(4096);
  . = . + 0x10000; /* <-- grow this value as much as you can, depending on free RAM availability */
  stack_top = .;

Note: with this approach, stack and heap basically share the same memory area. This means that if the stack or the heap grows "too much" it can overwrite the other one. It is therefore important to move the stack top (i.e. 0x10000 in the example) as much as possible.


Then, add the paths and names of the C++ libraries into the OIL file. For example, in case of the Linaro ARM toolchain:

  CFLAGS = "-I/path/to/aarch64-elf/aarch64-elf/include/c++/version/";
  CFLAGS = "-I/path/to/aarch64-elf/aarch64-elf/include/c++/version/aarch64-elf/";
  CFLAGS = "-I/path/to/aarch64-elf/aarch64-elf/libc/usr/include/";
  
  LDFLAGS = "-L /path/to/aarch64-elf/aarch64-elf/libc/usr/lib";
  LDFLAGS = "-L /path/to/aarch64-elf/aarch64-elf/lib/";  
  
  LIBS = "-l:libc.a";
  LIBS = "-l:libgcc.a";
  LIBS = "-l:librdimon.a";
  LIBS = "-l:libsupc++.a";