elf ELF loader

This example builds a small ELF loader test case. This includes several test programs under examples/elf tests. These tests are build using the relocatable ELF format and installed in a ROMFS file system. At run time, each program in the ROMFS file system is executed. Requires CONFIG_ELF. Other configuration options:

  • CONFIG_EXAMPLES_ELF_DEVMINOR – The minor device number of the ROMFS block driver. For example, the N in /dev/ramN. Used for registering the RAM block driver that will hold the ROMFS file system containing the ELF executables to be tested. Default: 0.

  • CONFIG_EXAMPLES_ELF_DEVPATH – The path to the ROMFS block driver device. This must match EXAMPLES_ELF_DEVMINOR. Used for registering the RAM block driver that will hold the ROMFS file system containing the ELF executables to be tested. Default: /dev/ram0.

Notes:

  1. CFLAGS should be provided in CELFFLAGS. RAM and FLASH memory regions may require long allcs. For ARM, this might be:

    CELFFLAGS = $(CFLAGS) -mlong-calls

    Similarly for C++ flags which must be provided in CXXELFFLAGS.

  2. Your top-level nuttx/Make.defs file must also include an appropriate definition, LDELFFLAGS, to generate a relocatable ELF object. With GNU LD, this should include -r and -e main (or _main on some platforms).:

    LDELFFLAGS = -r -e main

    If you use GCC to link, you make also need to include -nostdlib.

  3. This example also requires genromfs. genromfs can be build as part of the nuttx toolchain. Or can built from the genromfs sources that can be found in the NuttX tools repository (genromfs-0.5.2.tar.gz). In any event, the PATH variable must include the path to the genromfs executable.

  4. ELF size: The ELF files in this example are, be default, quite large because they include a lot of build garbage. You can greatly reduce the size of the ELF binaries are using the objcopy --strip-unneeded command to remove un-necessary information from the ELF files.

  5. Simulator. You cannot use this example with the NuttX simulator on Cygwin. That is because the Cygwin GCC does not generate ELF file but rather some Windows-native binary format.

    If you really want to do this, you can create a NuttX x86 buildroot toolchain and use that be build the ELF executables for the ROMFS file system.

  6. Linker scripts. You might also want to use a linker scripts to combine sections better. An example linker script is at nuttx/binfmt/libelf/gnu-elf.ld. That example might have to be tuned for your particular linker output to position additional sections correctly. The GNU LD LDELFFLAGS then might be:

    LDELFFLAGS = -r -e main -T$(TOPDIR)/binfmt/libelf/gnu-elf.ld