elf ELF loader

This example builds a small ELF loader test case. This includes several test programs under examples/elf tests. These tests are built using the relocatable ELF format and installed in a configurable file system. At run time, the file system is mounted and each program is executed. Requires CONFIG_ELF. Two distinct types of file systems are supported: internal (included in the NuttX binary) and external (not included in the binary). The external file systems need to be uploaded manually. For the internal file systems the sample supports the romfs and cromfs filesystems. For the external file systems any of the provided file systems can be used (vfat, …), but also the romfs filesystem for which the image (romfs.img) is automatically generated.

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. The arch Toolchain.defs sets CELFFLAGS, CXXELFFLAGS and LDELFFLAGS. For example, on ARM they contain -mlong-calls, the entry point _start and the linker script libs/libc/elf/gnu-elf.ld. A board scripts/Make.defs can add an option with +=, for example LDELFFLAGS += -melf32lriscv. Do not set these variables again with =: the board then loses the options that the arch adds for the configuration, for example crt0.o and the PIC and FDPIC options.

  2. 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.

  3. 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.

  4. When generating the romfs.img for external filesystem the image (romfs.img) needs to be manually copied to the start of the configured CONFIG_EXAMPLES_ELF_DEVPATH using openocd or your preferred programmer.