Want to understand the issue with BPFTRACE_HAVE_BTF

[the-prachi]

Hi Team - I have deployed latest version of bpftrace (appimage) in ubuntu 20.04. I am running tcpconnect.bt from tools section.
But while running the tcpconnect.bt, it gives me an error that sys/socket.h is not available.
I was looking at the code for tcpconnect.bt and it has following include files:

#ifndef BPFTRACE_HAVE_BTF
#include <linux/socket.h>
#include <net/sock.h>
#else
#include <sys/socket.h>
#endif

I also ran the script check_kernel_features.sh which returned that all features are available. Linux headers are also available.
Could you explain why the sys/socket.h is being called when BTF is enabled on the VM? What could be missing?

[viktormalik]

tcpconnect.bt uses the AF_INET and AF_INET6 macros which are defined in linux/socket.h but also in a userspace header sys/socket.h (should be in glibc headers). Since BTF doesn't contain macro definitions, we chose to include the userspace header as its definitions don't conflict with BTF definitions and therefore can be used simultaneously (which wouldn't be the case if we always included linux/socket.h).

TLDR; you need to install the glibc-headers package (or other package containing sys/socket.h).

[jordalgo]

I added a little comment to this file, which may help future users: #3055

[ajor]

If the question is "why is sys/socket.h used instead of linux/socket.h":
The first line of the if-macro is is an "if-n-def" (i.e. if-not-defined), not "if-def", so when BTF is detected on your system, sys/socket.h will be used.

[the-prachi]

Ok. So, I downloaded glibc-source and libc6 on my ubuntu VM, but still getting the same error that sys/socket.h file not found. So, I downloaded gcc and it started working. So, does that mean I need to have gcc on my machine for tcp_connect to work?

[viktormalik]

What distro is this?

[the-prachi]

Ubuntu 20.04

[the-prachi]

Also, another question is if I can add gcc as part of appimage. Will that suffice?

[viktormalik]

On Ubuntu, the file is a part of the libc6-dev package. The package is a dependency of gcc but you don't need to install gcc, just libc6-dev.