169 lines
5.6 KiB
Plaintext
169 lines
5.6 KiB
Plaintext
libpcode README
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===============
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Configuration Dependencies
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--------------------------
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In order to use this module, you must first install the P-Code virtual
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machine. You can get this from the Pascal package or from the NuttX Pascal
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GIT repository. See the README.txt file at the top-level Pascal for
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installation instructions. The correct location to install the P-code
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virtual machine is at apps/interpreters (assuming that you are using
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the NuttX apps/ package and that you have named the directory apps/).
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Other required configuration settings:
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CONFIG_NFILE_DESCRIPTORS > 3
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CONFIG_BINFMT_DISABLE=n
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CONFIG_PCODE=y
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Directory Contents
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------------------
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This directory holds support files for the P-Code binary format. For other
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binary formats, the library directory contains critical logic for the binary
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format. But this is not the case with the P-code binary format; since the
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binary file is interpreted, little additional support is necessary. As a
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result, this directory includes only a few files needed by the binfmt build
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logic and to support unit-level testing of the P-Code binary format.
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Files include in this directory include:
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1. This README.txt file
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2. Build support file:
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Kconfig, Make.defs
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3. Unit test support files:
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hello.pas -- Pascal "Hello, World!" source file
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hello.pex -- P-Code POFF format file created by compiling hello.pas
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romfs.img -- A ROMFS filsystem image created by:
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make image
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cp hello.pex image/.
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genromfs -f romfs.img -d image -V pofftest
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rm -rf image
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romfs.h -- a C header file containing the ROMFS file system in an
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initialized C structure. This file was created via:
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xxd -g 1 -i romfs.img >romfs.h
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then cleaned up with an editor to conform with NuttX coding standards.
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Also, the data definitions in the romfs.h file should be marked with
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'const' qualifier the so that the data will be stored in FLASH.
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Test Configuration
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------------------
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Here is a simple test configuration using the NuttX simulator:
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1. Install the sim/nsh configuration:
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cd tools
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./configure.sh sim/nsh
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cd ..
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2. Install p-code virtual machine as described above.
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3. Modify the configuration using 'make menuconfig'. Change the following
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selections:
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This enables general BINFMT support:
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CONFIG_DEBUG_BINFMT=y
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CONFIG_BINFMT_EXEPATH=y
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This enables building of the P-Code virtual machine:
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CONFIG_INTERPRETERS_PCODE=y
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And the P-Code runtime support:
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CONFIG_SYSTEM_PRUN=y
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This enables building the PCODE binary format
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CONFIG_PCODE=y
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CONFIG_PCODE_PRIORITY=100
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CONFIG_PCODE_STACKSIZE=2048
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This enables building and mount a test filesystem:
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CONFIG_PCODE_TEST_FS=y
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CONFIG_PCODE_TEST_DEVMINOR=3
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CONFIG_PCODE_TEST_DEVPATH="/dev/ram3"
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CONFIG_PCODE_TEST_MOUNTPOINT="/bin"
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Debug options can also be enabled with:
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CONFIG_DEBUG_FEATURES=y
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CONFIG_DEBUG_BINFMT=y
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CONFIG_DEBUG_INFO=y
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4. In lieu of a a real test application, this Quick'n'Dirty patch can be used
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to initialize the P-Code binary format:
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@@ -115,6 +115,7 @@ const struct symtab_s CONFIG_EXECFUNCS_SYMTAB[1];
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/****************************************************************************
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* Name: nsh_main
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****************************************************************************/
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+int pcode_initialize(void);
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int nsh_main(int argc, char *argv[])
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{
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@@ -143,6 +144,7 @@ int nsh_main(int argc, char *argv[])
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exitval = 1;
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}
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#endif
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+(void)pcode_initialize();
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/* Initialize the NSH library */
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5. Then after building nuttx.exe you should be able to run the P-Code hello
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world example like:
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nsh> hello.pex
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Issues
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------
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1. As implemented now, there is a tight coupling between the nuttx/directory
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and the apps/ directory. That should not be the case; the nuttx/ logic
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should be completely independent of apps/ logic (but not vice versa).
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2. The current implementation will not work in the CONFIG_BUILD_PROTECTED or
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CONFIG_BUILD_KERNEL configurations. That is because of the little proxy
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logic (function pcode_proxy() in the file pcode.c). (a) That logic would
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attempt to link with P-code logic that resides in user space. That will
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not work. And (2) that proxy would be started in user mode but in the
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kernel address space which will certainly crash immediately.
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The general idea to fix both of these problems is as follows:
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1. Eliminate the pcode_proxy. Instead start a P-Code execution program that
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resides in the file system. That P-Code execution program already
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exists. It is in apps/system/prun. This program should be built as,
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say, an ELF binary and installed in a file system.
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2. Add a configuration setting that gives the full path to where the pexec
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program is stored in the filesystem.
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3. Modify the logic so that the P-Code execution program runs (instead of
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the requested program) an it received the full path the the P-Code file
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on the command line. This might be accomplished by simply modifying the
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argv[] structure in the struct binary_s instance.
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The current start-up logic in binfmt_execmodule.c would have modified to
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handle this special start-up. Perhaps the struct binfmt_s could be
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extended to include an exec() method that provides custom start up logic?
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4. Add a task start hook to the program. Here is where we can setup up the
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on_exit() function that will clean up after the P-Code program terminates.
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There are many other smaller issues to be resolved, but those are the main
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ones.
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A more complex solution might include a user-space p-code daemon that
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receives the P-Code path in a POSIX message and starts a P-Code interpreter
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thread wholly in user space.
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