Feature-gate `no_std` and `no_main`

The `no_std` and `no_main` attributes are only needed when we compile
the eBPF kernels for the "bpf" architecture. By feature-gating them on
the target architecture, we ensure the kernels compile just fine on a
host-architecture like x64. They won't be able to do anything
meaningfully but it is useful within the context of the larger workspace
they are embedded in as it allows `cargo build --workspace` and `cargo
test --workspace` to just work.

test/integration-ebpf/src/bpf_probe_read.rs

@@ -1,5 +1,5 @@
-#![no_std]
-#![no_main]
+#![cfg_attr(target_arch = "bpf", no_std)]
+#![cfg_attr(target_arch = "bpf", no_main)]
 
 use aya_ebpf::{
     helpers::{bpf_probe_read_kernel_str_bytes, bpf_probe_read_user_str_bytes},
@@ -77,3 +77,8 @@ pub fn test_bpf_probe_read_kernel_str_bytes(ctx: ProbeContext) {
 fn panic(_info: &core::panic::PanicInfo) -> ! {
     loop {}
 }
+
+#[cfg(not(target_arch = "bpf"))]
+fn main() {
+    panic!("This should only ever be called from its eBPF entrypoint")
+}

test/integration-ebpf/src/lib.rs

@@ -1,3 +1,3 @@
-#![no_std]
+#![cfg_attr(target_arch = "bpf", no_std)]
 
 // This file exists to enable the library target.

test/integration-ebpf/src/log.rs

@@ -1,5 +1,5 @@
-#![no_std]
-#![no_main]
+#![cfg_attr(target_arch = "bpf", no_std)]
+#![cfg_attr(target_arch = "bpf", no_main)]
 
 use core::net::{IpAddr, Ipv4Addr, Ipv6Addr};
 
@@ -87,3 +87,8 @@ pub fn test_log(ctx: ProbeContext) {
 fn panic(_info: &core::panic::PanicInfo) -> ! {
     loop {}
 }
+
+#[cfg(not(target_arch = "bpf"))]
+fn main() {
+    panic!("This should only ever be called from its eBPF entrypoint")
+}

test/integration-ebpf/src/map_test.rs

@@ -1,8 +1,8 @@
 // Socket Filter program for testing with an arbitrary program with maps.
 // This is mainly used in tests with consideration for old kernels.
 
-#![no_std]
-#![no_main]
+#![cfg_attr(target_arch = "bpf", no_std)]
+#![cfg_attr(target_arch = "bpf", no_main)]
 
 use aya_ebpf::{
     macros::{map, socket_filter},
@@ -41,3 +41,8 @@ pub fn simple_prog(_ctx: SkBuffContext) -> i64 {
 fn panic(_info: &core::panic::PanicInfo) -> ! {
     loop {}
 }
+
+#[cfg(not(target_arch = "bpf"))]
+fn main() {
+    panic!("This should only ever be called from its eBPF entrypoint")
+}

test/integration-ebpf/src/memmove_test.rs

@@ -1,5 +1,5 @@
-#![no_std]
-#![no_main]
+#![cfg_attr(target_arch = "bpf", no_std)]
+#![cfg_attr(target_arch = "bpf", no_main)]
 
 use core::mem;
 
@@ -59,3 +59,8 @@ fn try_do_dnat(ctx: XdpContext) -> Result<u32, ()> {
 fn panic(_info: &core::panic::PanicInfo) -> ! {
     loop {}
 }
+
+#[cfg(not(target_arch = "bpf"))]
+fn main() {
+    panic!("This should only ever be called from its eBPF entrypoint")
+}

test/integration-ebpf/src/name_test.rs

@@ -1,5 +1,5 @@
-#![no_std]
-#![no_main]
+#![cfg_attr(target_arch = "bpf", no_std)]
+#![cfg_attr(target_arch = "bpf", no_main)]
 
 use aya_ebpf::{bindings::xdp_action, macros::xdp, programs::XdpContext};
 
@@ -20,3 +20,8 @@ unsafe fn try_pass(_ctx: XdpContext) -> Result<u32, u32> {
 fn panic(_info: &core::panic::PanicInfo) -> ! {
     loop {}
 }
+
+#[cfg(not(target_arch = "bpf"))]
+fn main() {
+    panic!("This should only ever be called from its eBPF entrypoint")
+}

test/integration-ebpf/src/pass.rs

@@ -1,5 +1,5 @@
-#![no_std]
-#![no_main]
+#![cfg_attr(target_arch = "bpf", no_std)]
+#![cfg_attr(target_arch = "bpf", no_main)]
 
 use aya_ebpf::{bindings::xdp_action, macros::xdp, programs::XdpContext};
 
@@ -22,3 +22,8 @@ unsafe fn try_pass(_ctx: XdpContext) -> Result<u32, u32> {
 fn panic(_info: &core::panic::PanicInfo) -> ! {
     loop {}
 }
+
+#[cfg(not(target_arch = "bpf"))]
+fn main() {
+    panic!("This should only ever be called from its eBPF entrypoint")
+}

test/integration-ebpf/src/raw_tracepoint.rs

@@ -1,5 +1,5 @@
-#![no_std]
-#![no_main]
+#![cfg_attr(target_arch = "bpf", no_std)]
+#![cfg_attr(target_arch = "bpf", no_main)]
 
 use aya_ebpf::{
     macros::{map, raw_tracepoint},
@@ -31,3 +31,8 @@ pub fn sys_enter(ctx: RawTracePointContext) -> i32 {
 fn panic(_info: &core::panic::PanicInfo) -> ! {
     loop {}
 }
+
+#[cfg(not(target_arch = "bpf"))]
+fn main() {
+    panic!("This should only ever be called from its eBPF entrypoint")
+}

test/integration-ebpf/src/redirect.rs

@@ -1,5 +1,5 @@
-#![no_std]
-#![no_main]
+#![cfg_attr(target_arch = "bpf", no_std)]
+#![cfg_attr(target_arch = "bpf", no_main)]
 
 use aya_ebpf::{
     bindings::xdp_action,
@@ -80,3 +80,8 @@ fn inc_hit(index: u32) {
 fn panic(_info: &core::panic::PanicInfo) -> ! {
     loop {}
 }
+
+#[cfg(not(target_arch = "bpf"))]
+fn main() {
+    panic!("This should only ever be called from its eBPF entrypoint")
+}

test/integration-ebpf/src/relocations.rs

@@ -1,5 +1,5 @@
-#![no_std]
-#![no_main]
+#![cfg_attr(target_arch = "bpf", no_std)]
+#![cfg_attr(target_arch = "bpf", no_main)]
 
 use core::hint;
 
@@ -44,3 +44,8 @@ fn set_result_backward(index: u32, value: u64) {
 fn panic(_info: &core::panic::PanicInfo) -> ! {
     loop {}
 }
+
+#[cfg(not(target_arch = "bpf"))]
+fn main() {
+    panic!("This should only ever be called from its eBPF entrypoint")
+}

test/integration-ebpf/src/ring_buf.rs

@@ -1,5 +1,5 @@
-#![no_std]
-#![no_main]
+#![cfg_attr(target_arch = "bpf", no_std)]
+#![cfg_attr(target_arch = "bpf", no_main)]
 
 use aya_ebpf::{
     macros::{map, uprobe},
@@ -51,3 +51,8 @@ pub fn ring_buf_test(ctx: ProbeContext) {
 fn panic(_info: &core::panic::PanicInfo) -> ! {
     loop {}
 }
+
+#[cfg(not(target_arch = "bpf"))]
+fn main() {
+    panic!("This should only ever be called from its eBPF entrypoint")
+}

test/integration-ebpf/src/simple_prog.rs

@@ -1,8 +1,8 @@
 // Socket Filter program for testing with an arbitrary program.
 // This is mainly used in tests with consideration for old kernels.
 
-#![no_std]
-#![no_main]
+#![cfg_attr(target_arch = "bpf", no_std)]
+#![cfg_attr(target_arch = "bpf", no_main)]
 
 use aya_ebpf::{macros::socket_filter, programs::SkBuffContext};
 
@@ -17,3 +17,8 @@ pub fn simple_prog(_ctx: SkBuffContext) -> i64 {
 fn panic(_info: &core::panic::PanicInfo) -> ! {
     loop {}
 }
+
+#[cfg(not(target_arch = "bpf"))]
+fn main() {
+    panic!("This should only ever be called from its eBPF entrypoint")
+}

test/integration-ebpf/src/strncmp.rs

@@ -1,5 +1,5 @@
-#![no_std]
-#![no_main]
+#![cfg_attr(target_arch = "bpf", no_std)]
+#![cfg_attr(target_arch = "bpf", no_main)]
 
 use aya_ebpf::{
     cty::c_long,
@@ -32,3 +32,8 @@ pub fn test_bpf_strncmp(ctx: ProbeContext) -> Result<(), c_long> {
 fn panic(_info: &core::panic::PanicInfo) -> ! {
     loop {}
 }
+
+#[cfg(not(target_arch = "bpf"))]
+fn main() {
+    panic!("This should only ever be called from its eBPF entrypoint")
+}

test/integration-ebpf/src/tcx.rs

@@ -1,5 +1,5 @@
-#![no_std]
-#![no_main]
+#![cfg_attr(target_arch = "bpf", no_std)]
+#![cfg_attr(target_arch = "bpf", no_main)]
 
 use aya_ebpf::{bindings::tcx_action_base::TCX_NEXT, macros::classifier, programs::TcContext};
 
@@ -13,3 +13,8 @@ pub fn tcx_next(_ctx: TcContext) -> i32 {
 fn panic(_info: &core::panic::PanicInfo) -> ! {
     loop {}
 }
+
+#[cfg(not(target_arch = "bpf"))]
+fn main() {
+    panic!("This should only ever be called from its eBPF entrypoint")
+}

test/integration-ebpf/src/test.rs

@@ -1,5 +1,5 @@
-#![no_std]
-#![no_main]
+#![cfg_attr(target_arch = "bpf", no_std)]
+#![cfg_attr(target_arch = "bpf", no_main)]
 
 use aya_ebpf::{
     bindings::{bpf_ret_code, xdp_action},
@@ -58,3 +58,8 @@ pub fn test_flow(_ctx: FlowDissectorContext) -> u32 {
 fn panic(_info: &core::panic::PanicInfo) -> ! {
     loop {}
 }
+
+#[cfg(not(target_arch = "bpf"))]
+fn main() {
+    panic!("This should only ever be called from its eBPF entrypoint")
+}

test/integration-ebpf/src/two_progs.rs

@@ -1,7 +1,7 @@
 // Two programs in the same ELF section
 
-#![no_std]
-#![no_main]
+#![cfg_attr(target_arch = "bpf", no_std)]
+#![cfg_attr(target_arch = "bpf", no_main)]
 
 use aya_ebpf::{macros::tracepoint, programs::TracePointContext};
 
@@ -19,3 +19,8 @@ pub fn test_tracepoint_two(_ctx: TracePointContext) -> u32 {
 fn panic(_info: &core::panic::PanicInfo) -> ! {
     loop {}
 }
+
+#[cfg(not(target_arch = "bpf"))]
+fn main() {
+    panic!("This should only ever be called from its eBPF entrypoint")
+}

test/integration-ebpf/src/uprobe_cookie.rs

@@ -1,5 +1,5 @@
-#![no_std]
-#![no_main]
+#![cfg_attr(target_arch = "bpf", no_std)]
+#![cfg_attr(target_arch = "bpf", no_main)]
 
 use aya_ebpf::{
     EbpfContext as _, helpers,
@@ -23,3 +23,8 @@ pub fn uprobe_cookie(ctx: ProbeContext) {
 fn panic(_info: &core::panic::PanicInfo) -> ! {
     loop {}
 }
+
+#[cfg(not(target_arch = "bpf"))]
+fn main() {
+    panic!("This should only ever be called from its eBPF entrypoint")
+}

test/integration-ebpf/src/xdp_sec.rs

@@ -1,5 +1,5 @@
-#![no_std]
-#![no_main]
+#![cfg_attr(target_arch = "bpf", no_std)]
+#![cfg_attr(target_arch = "bpf", no_main)]
 
 use aya_ebpf::{bindings::xdp_action::XDP_PASS, macros::xdp, programs::XdpContext};
 
@@ -24,3 +24,8 @@ probe!(xdp_frags_devmap, (frags, map = "devmap"));
 fn panic(_info: &core::panic::PanicInfo) -> ! {
     loop {}
 }
+
+#[cfg(not(target_arch = "bpf"))]
+fn main() {
+    panic!("This should only ever be called from its eBPF entrypoint")
+}