Issue building with feature kern

When trying to building bpf-recorder-kern, kern feature must be enabled.

Steps to reproduce:

git clone git@github.com:openmina/mina-network-debugger.git network-debugger
CARGO_TARGET_DIR=target/bpf cargo +nightly-2022-10-10 rustc --package=bpf-recorder --bin=bpf-recorder-kern --features=kern --no-default-features --target=bpfel-unknown-none -Z build-std=core --release -- -Cdebuginfo=2 -Clink-arg=--disable-memory-builtins -Clink-arg=--keep-btf
cargo run --bin bpf-recorder-kern --features="kern"

This gives following error:

   Compiling bpf-recorder v0.1.0 (/home/mimir/0xMimir/work/network-debugger/bpf-recorder)
error[E0433]: failed to resolve: use of undeclared crate or module `std`
 --> bpf-recorder/src/proc.rs:2:5
  |
2 | use std::{
  |     ^^^ use of undeclared crate or module `std`

error[E0433]: failed to resolve: use of undeclared crate or module `std`
  --> bpf-recorder/src/lib.rs:95:9
   |
95 |     use std::net::{IpAddr, SocketAddr};
   |         ^^^ use of undeclared crate or module `std`

error[E0432]: unresolved import `std`
 --> bpf-recorder/src/proc.rs:2:5
  |
2 | use std::{
  |     ^^^ use of undeclared crate or module `std`

error: cannot find macro `format` in this scope
  --> bpf-recorder/src/proc.rs:14:32
   |
14 |         let mut f = File::open(format!("/proc/{pid}/cmdline"))?;
   |                                ^^^^^^

error[E0433]: failed to resolve: use of undeclared crate or module `std`
   --> bpf-recorder/src/lib.rs:172:17
    |
172 |                 std::process::exit(1);
    |                 ^^^ use of undeclared crate or module `std`

error[E0412]: cannot find type `String` in this scope
   --> bpf-recorder/src/lib.rs:113:16
    |
113 |         NewApp(String),
    |                ^^^^^^ not found in this scope
    |
help: there is an enum variant `serde::__private::de::Content::String` and 1 other; try using the variant's enum
    |
113 |         NewApp(serde::__private::de::Content),
    |                ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
113 |         NewApp(serde_json::Value),
    |                ~~~~~~~~~~~~~~~~~

error[E0412]: cannot find type `Vec` in this scope
   --> bpf-recorder/src/lib.rs:119:22
    |
119 |         IncomingData(Vec<u8>),
    |                      ^^^ not found in this scope
    |
help: consider importing this struct
    |
95  +     use serde::__private::Vec;
    |

error[E0412]: cannot find type `Vec` in this scope
   --> bpf-recorder/src/lib.rs:120:22
    |
120 |         OutgoingData(Vec<u8>),
    |                      ^^^ not found in this scope
    |
help: consider importing this struct
    |
95  +     use serde::__private::Vec;
    |

error[E0412]: cannot find type `Vec` in this scope
   --> bpf-recorder/src/lib.rs:121:16
    |
121 |         Random(Vec<u8>),
    |                ^^^ not found in this scope
    |
help: consider importing this struct
    |
95  +     use serde::__private::Vec;
    |

error[E0412]: cannot find type `Vec` in this scope
   --> bpf-recorder/src/lib.rs:122:20
    |
122 |         GetSockOpt(Vec<u8>),
    |                    ^^^ not found in this scope
    |
help: consider importing this struct
    |
95  +     use serde::__private::Vec;
    |

error[E0433]: failed to resolve: use of undeclared type `String`
  --> bpf-recorder/src/proc.rs:15:21
   |
15 |         let mut s = String::new();
   |                     ^^^^^^ use of undeclared type `String`
   |
help: there is an enum variant `serde::__private::de::Content::String` and 1 other; try using the variant's enum
   |
15 |         let mut s = serde::__private::de::Content();
   |                     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
15 |         let mut s = serde_json::Value();
   |                     ~~~~~~~~~~~~~~~~~

error[E0433]: failed to resolve: use of undeclared type `String`
   --> bpf-recorder/src/lib.rs:203:21
    |
203 |                     String::from_utf8(data[..(data.len() - 1)].to_vec())
    |                     ^^^^^^ use of undeclared type `String`
    |
help: there is an enum variant `serde::__private::de::Content::String` and 1 other; try using the variant's enum
    |
203 |                     serde::__private::de::Content(data[..(data.len() - 1)].to_vec())
    |                     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
203 |                     serde_json::Value(data[..(data.len() - 1)].to_vec())
    |                     ~~~~~~~~~~~~~~~~~

error[E0599]: no method named `to_string` found for reference `&'static str` in the current scope
   --> bpf-recorder/src/lib.rs:204:57
    |
204 |                         .unwrap_or("invalid_uft8_alias".to_string()),
    |                                                         ^^^^^^^^^ method not found in `&str`
    |
    = help: items from traits can only be used if the trait is in scope
help: the following trait is implemented but not in scope; perhaps add a `use` for it:
    |
95  +     use tinyvec::alloc::string::ToString;
    |

Some errors have detailed explanations: E0412, E0432, E0433, E0599.
For more information about an error, try `rustc --explain E0412`.
error: could not compile `bpf-recorder` (lib) due to 13 previous errors

openmina / mina-network-debugger

Issue building with feature kern #45