More ELF loader changes

git-svn-id: http://svn.code.sf.net/p/nuttx/code/trunk@5261 42af7a65-404d-4744-a932-0658087f49c3

apps/examples/README.txt

@@ -297,6 +297,53 @@ examples/discover
     CONFIG_EXAMPLES_DISCOVER_DRIPADDR - Router IP address
     CONFIG_EXAMPLES_DISCOVER_NETMASK - Network Mask
 
+examples/elf
+^^^^^^^^^^^^
+
+  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.
+      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. Your top-level nuttx/Make.defs file must include an approproate 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' or 
+     '-nostartfiles' and '-nodefaultlibs'.
+
+  2. 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
+     at misc/tools/genromfs-0.5.2.tar.gz.  In any event, the PATH variable must
+     include the path to the genromfs executable.
+
+  3. ELF size:  The ELF files in this example are, be default, quite large
+     because they include a lot of "build garbage".  You can greately reduce the
+     size of the ELF binaries are using the objcopy --strip-unneeded command to
+     remove un-necessary information from the ELF files.
+
+  4. Simulator.  You cannot use this example with the 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.
+
 examples/ftpc
 ^^^^^^^^^^^^^