bpf: Remove builtin global functions

This commit removes memset and memcpy, relying instead on
implementations provided by std/compiler-builtins.

This commit adds `#![no_builtins]` to all the BPF programs written in
Rust, and the same should be propagated to aya-template and all examples
in the book and elsewhere before this commit is merged.

It turns out that without the `#![no_builtins]` annotation rustc
generates LLVM IR that calls LLVM intrinsics rather than libcalls. These
may end up as libcalls after lowering, but not before emitting errors in
BPF lowering[0].

This works thanks to rust-lang/rust#113716 which
causes `#![no_builtins]` to behave similarly to `-fno-builtin` in clang,
which was added in https://reviews.llvm.org/D68028 with similar
motivation.

This commit implies that we now require rustc nightly >= 2023-07-20.

[0] https://github.com/llvm/llvm-project/blob/7b2745b/llvm/lib/Target/BPF/BPFISelLowering.cpp#L472-L474

Author: tamird

ebpf/aya-ebpf/src/lib.rs

@@ -69,50 +69,6 @@ pub trait EbpfContext {
     }
 }
 
-mod intrinsics {
-    use super::cty::c_int;
-
-    #[unsafe(no_mangle)]
-    unsafe extern "C" fn memset(s: *mut u8, c: c_int, n: usize) {
-        #[expect(clippy::cast_sign_loss)]
-        let b = c as u8;
-        for i in 0..n {
-            unsafe { *s.add(i) = b }
-        }
-    }
-
-    #[unsafe(no_mangle)]
-    unsafe extern "C" fn memcpy(dest: *mut u8, src: *mut u8, n: usize) {
-        unsafe { copy_forward(dest, src, n) }
-    }
-
-    #[unsafe(no_mangle)]
-    unsafe extern "C" fn memmove(dest: *mut u8, src: *mut u8, n: usize) {
-        let delta = (dest as usize).wrapping_sub(src as usize);
-        if delta >= n {
-            // We can copy forwards because either dest is far enough ahead of src,
-            // or src is ahead of dest (and delta overflowed).
-            unsafe { copy_forward(dest, src, n) }
-        } else {
-            unsafe { copy_backward(dest, src, n) }
-        }
-    }
-
-    #[inline(always)]
-    unsafe fn copy_forward(dest: *mut u8, src: *mut u8, n: usize) {
-        for i in 0..n {
-            unsafe { *dest.add(i) = *src.add(i) }
-        }
-    }
-
-    #[inline(always)]
-    unsafe fn copy_backward(dest: *mut u8, src: *mut u8, n: usize) {
-        for i in (0..n).rev() {
-            unsafe { *dest.add(i) = *src.add(i) }
-        }
-    }
-}
-
 /// Check if a value is within a range, using conditional forms compatible with
 /// the verifier.
 #[inline(always)]

test/integration-ebpf/src/array.rs

@@ -1,5 +1,6 @@
-#![no_std]
+#![no_builtins]
 #![no_main]
+#![no_std]
 #![expect(unused_crate_dependencies, reason = "used in other bins")]
 
 #[cfg(not(test))]

test/integration-ebpf/src/bpf_probe_read.rs

@@ -1,5 +1,6 @@
-#![no_std]
+#![no_builtins]
 #![no_main]
+#![no_std]
 #![expect(unused_crate_dependencies, reason = "used in other bins")]
 
 use aya_ebpf::{

test/integration-ebpf/src/lib.rs

@@ -1,3 +1,4 @@
+#![no_builtins]
 #![no_std]
 #![expect(unused_crate_dependencies, reason = "used in bins")]
 

test/integration-ebpf/src/linear_data_structures.rs

@@ -1,5 +1,6 @@
-#![no_std]
+#![no_builtins]
 #![no_main]
+#![no_std]
 #![expect(unused_crate_dependencies, reason = "used in other bins")]
 
 #[cfg(not(test))]

test/integration-ebpf/src/log.rs

@@ -1,5 +1,6 @@
-#![no_std]
+#![no_builtins]
 #![no_main]
+#![no_std]
 #![expect(unused_crate_dependencies, reason = "used in other bins")]
 
 use core::{

test/integration-ebpf/src/map_test.rs

@@ -1,5 +1,6 @@
-#![no_std]
+#![no_builtins]
 #![no_main]
+#![no_std]
 #![expect(unused_crate_dependencies, reason = "used in other bins")]
 
 use aya_ebpf::{

test/integration-ebpf/src/memmove_test.rs

@@ -1,5 +1,6 @@
-#![no_std]
+#![no_builtins]
 #![no_main]
+#![no_std]
 #![expect(unused_crate_dependencies, reason = "used in other bins")]
 
 use core::mem;

test/integration-ebpf/src/name_test.rs

@@ -1,5 +1,6 @@
-#![no_std]
+#![no_builtins]
 #![no_main]
+#![no_std]
 #![expect(unused_crate_dependencies, reason = "used in other bins")]
 
 use aya_ebpf::{bindings::xdp_action, macros::xdp, programs::XdpContext};

test/integration-ebpf/src/pass.rs

@@ -1,5 +1,6 @@
-#![no_std]
+#![no_builtins]
 #![no_main]
+#![no_std]
 #![expect(unused_crate_dependencies, reason = "used in other bins")]
 
 use aya_ebpf::{bindings::xdp_action, macros::xdp, programs::XdpContext};