Instructions to generate and compile code for Example 1

First, run this Python program:

$ ./example1-generator.py --num-fields 32

That will write to these two files:

• generated_my_custom_hdr_fields.p4
• generated_read_write_custom_header_at_index.p4

Copies of the files as generated on my system when I was developing it are included in the generated-files directory, in case you want to look at them without generating them yourself.

Both of those files have #include directives in the program example1.p4, which you can now compile:

$ p4c --target bmv2 --arch v1model example1.p4

When developing and debugging programs where parts of them are auto-generated, it can often be helpful to look at the final version after all of the code generation is complete, and the #include directives have been processed. Executing the p4c command will create a file example1.p4i that contains exactly that. It will still contain some lines that look like this:

# 39 "example1.p4" 2

These are used by the P4 compiler to track which original input file and line number each line of code came from, so when it generates error or warning messages, they can mention the correct file and line number of the files before the preprocessor ran, rather than after. Such lines have no effect on the execution behavior of the P4 program.

Such a .p4i file will also contain the full contents of the v1model.p4 #include file, which you will likely want to skip over. Using your text editor to search for occurrences of the file name you are interested in, e.g. example.p4, can be useful for that.

Note that I have written the example1-generator.py program to accept a command line parameter with the number of fields to generate. This can be generalized to any number of parameters you wish, or files of data, etc., that can be used by your Python (or other language) program to generate the code you wish, subject only to the limits of your imagination and time.