Bcc: Print BPF bytecode

[avgsg]

Hi!

Is there any way to print the resulting BPF bytecode from b = BPF(src_file="my_prog.c", debug=0)? Eg.: a simply b.print() that displays the bytecodes of b.

[pchaigno]

b = BPF(src_file="my_prog.c", debug=2)

will print the bytecode. debug=4 prints the intermediate C (rewritten by bcc).

[avgsg]

Well, not really working in some cases. I have tried the program below.

my_counter.c.zip

I'm getting the output below. There is a warning but no errors. I only get the object's address, similar to debug=0.

>>> BPF(src_file="my_counter.c", debug=2) In file included from /virtual/main.c:6: In file included from include/linux/skbuff.h:29: In file included from include/linux/net.h:28: include/linux/fs.h:2659:9: warning: comparison of unsigned enum expression < 0 is always false [-Wtautological-compare] if (id < 0 || id >= READING_MAX_ID) ~~ ^ ~ 1 warning generated. <bcc.BPF object at 0x7f094310c690>

Does anyone have any idea on what's going on?

[palmtenor]

When you set debug to be 2 (i.e. DEBUG_BPF), the library will print out the BPF bytecode when you load the function. You don't need to print the BPF object.

[avgsg]

Yes, I have realized that however it's not working for some cases. I could not spot an error. As an example, take my last comment above. The said program (my_counter.c.zip) does not result in any bytecodes even though debug is set to 2.

[yonghong-song]

In your my_counter.c, the bpf program is not auto-recognizable by bcc. It needs explicit load.
Hence, BPF(src_file="my_counter.c", debug=2) will not dump the byte code to you since
the program has not been loaded into the kernel.

[avgsg]

Thanks!! It works fine now.