[PATCH proxmox v4 01/45] ebpf: build: keep the build directory out of the BPF objects

[Hannes Laimer <h.laimer@proxmox.com>]

A subsystem's pinned state is keyed by the bytes of its object, and
the debug info that BTF needs carries the source paths. The same
program built from another directory therefore got a new fingerprint.
A version bump of the crate alone, built from a path that carries the
version, made every node reinstall the programs on its next pass.

Signed-off-by: Hannes Laimer <h.laimer@proxmox.com>
---
 proxmox-ebpf/build.rs | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/proxmox-ebpf/build.rs b/proxmox-ebpf/build.rs
index 5ac1df60bbcd..8a2577957a75 100644
--- a/proxmox-ebpf/build.rs
+++ b/proxmox-ebpf/build.rs
@@ -172,6 +172,10 @@ fn compile_bpf(
         // the host target only
         .arg("-I")
         .arg(format!("/usr/include/{}", multiarch()));
+    // the pinned state is keyed by the object's bytes, and -g writes the source paths into it, so
+    // a build from another directory would count as another program
+    let manifest_dir = env::var("CARGO_MANIFEST_DIR").unwrap();
+    cmd.arg(format!("-ffile-prefix-map={manifest_dir}=."));
     if debug {
         cmd.arg("-DBPF_DEBUG");
     }
-- 
2.47.3