docs: Document breaking changes

This provides a `BREAKING-CHANGES.md` that we can populate per-crate.
Doing so will allow us to pull this content into our changelog and
websites to make things easier for users.

Signed-off-by: Dave Tucker <[email protected]>

aya/BREAKING-CHANGES.md

@@ -0,0 +1,98 @@
+# Breaking Changes
+
+This document contains a list of breaking changes in each version and some notes to help migrate
+between versions. It is compiled manually from the commit history and changelog. We also tag PRs on
+github with a [breaking change] label.
+
+[breaking change]: (https://github.com/aya-rs/aya/issues?q=label%3A%22breaking+change%22)
+
+## Summary
+
+- [v0.12.0](#v0120)
+  - In `aya::Bpf::programs`, `name` uses the function name from the ELF file
+
+## v0.12.0
+
+### In `aya::Bpf::programs`, `name` uses the function name from the ELF file
+
+In previous versions, the `name` parameter of `aya::Bpf::programs` was
+derived from the ELF section name. If you were using `aya-bpf`, this was sensible
+since our macros took care of appending the function name to the section name,
+resulting in a section name like `kprobe/my_function`. However, loading this
+program using libbpf > 1.0 would fail due the section name not following the
+newly enforced [naming convention].
+
+Likewise, loading eBPF programs written in C using Aya was also problematic.
+Given the following C program:
+
+```c
+SEC("kprobe")
+int my_function(struct pt_regs *ctx) {
+    return 0;
+}
+```
+
+Loading this program using Aya would require the following:
+
+```rust
+let bpf = Bpf::load(&program)?;
+let my_function = bpf.program("kprobe")?;
+```
+
+This was not intuitive and was a frequent source of confusion.
+
+To solve this, Aya was changed to resolve function names from the ELF files
+symbol table. Therefore, if your function is defined as:
+
+```rust
+#[kprobe]
+fn my_function(_ctx: KprobeContext) -> i32 {
+    0
+}
+```
+
+Or in C:
+
+```c
+SEC("kprobe")
+int my_function(struct pt_regs *ctx) {
+    return 0;
+}
+```
+
+Then you should load it using:
+
+```rust
+let bpf = Bpf::load(&program)?;
+let my_function = bpf.program("my_function")?;
+```
+
+Migration is straightforward.
+Simply replace the `name` parameter in `Bpf::programs` with the function name
+from the ELF file.
+
+If you are using `aya-bpf`, you should update to the latest (git)
+version and recompile your programs. The name argument inside our macros
+has been deprecated and should therefore be removed.
+
+Given the following:
+
+```rust
+#[kprobe(name="another_name")]
+fn some_name(_ctx: KprobeContext) -> i32 {
+    0
+}
+```
+
+You would update it to:
+
+```rust
+#[kprobe]
+fn another_name(_ctx: KprobeContext) -> i32 {
+    0
+}
+```
+
+Note here that changing the exported function name is not supported anymore.
+
+[naming convention]: https://docs.kernel.org/bpf/libbpf/program_types.html