Subject: Three patches which collectively enable BTF debug info in BPF kernel

From: Brennan Vincent <[email-masked]>
Date: Sat, 24 Feb 2024 20:09:09 -0500

This configuration causes /sys/kernel/btf/vmlinux to exist, which is
necessary for some eBPF programs (e.g. those that rely on the "BPF
CO-RE" feature; see
https://docs.kernel.org/bpf/libbpf/libbpf_overview.html for details).

The initial two patches introduce userland packages that enable building
the kernel with this configuration, and the third one changes the kernel
config.

>From f02af354b559d53009a96d00c0f58a72957678d9 Mon Sep 17 00:00:00 2001
Message-ID: <[email-masked]>
From: Brennan Vincent <[email-masked]>
Date: Sat, 24 Feb 2024 09:34:22 -0500
Subject: [PATCH 1/3] gnu: Add libbpf 1.1.0

* gnu/packages/linux.scm (libbpf-1.1.0): New variable.

Change-Id: I5492541a6279a73a1a3fe25381c187168e2dd253
---
 gnu/packages/linux.scm | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/gnu/packages/linux.scm b/gnu/packages/linux.scm
index ef225479ca..8c665d436d 100644
--- a/gnu/packages/linux.scm
+++ b/gnu/packages/linux.scm
@@ -9660,6 +9660,20 @@ (define-public libbpf
 headers.")
     (license `(,license:lgpl2.1 ,license:bsd-2))))
 
+(define-public libbpf-1.1.0
+  (package
+    (inherit libbpf)
+    (version "1.1.0")
+    (source
+     (origin
+       (method git-fetch)
+       (uri (git-reference
+             (url "https://github.com/libbpf/libbpf")
+             (commit (string-append "v" version))))
+       (file-name (git-file-name (package-name libbpf) version))
+       (sha256
+        (base32 "0rh8828cridphkmynb3nhdcd8l37i11885kmnp2hilk81lh7myzy"))))))
+
 (define-public bcc
   (package
     (name "bcc")

base-commit: de24aaf13b17d6c019f3f240fd0eb0e1b8654970
-- 
2.41.0

>From 8b7fa6a86b6e1a7956b6941ecfac337ec6ad0abe Mon Sep 17 00:00:00 2001
Message-ID: <[email-masked]>
In-Reply-To: <[email-masked]>
References: <[email-masked]>
From: Brennan Vincent <[email-masked]>
Date: Sat, 24 Feb 2024 09:37:44 -0500
Subject: [PATCH 2/3] gnu: Add dwarves.

* gnu/packages/cpp.scm (dwarves): New variable.

Change-Id: I4d29732c1c04044f66d17b7f0ebc308e0e8134aa
---
 gnu/packages/cpp.scm | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/gnu/packages/cpp.scm b/gnu/packages/cpp.scm
index e530d1d2a8..58c2da019e 100644
--- a/gnu/packages/cpp.scm
+++ b/gnu/packages/cpp.scm
@@ -84,6 +84,7 @@ (define-module (gnu packages cpp)
   #:use-module (gnu packages curl)
   #:use-module (gnu packages datastructures)
   #:use-module (gnu packages disk)
+  #:use-module (gnu packages elf)
   #:use-module (gnu packages documentation)
   #:use-module (gnu packages fontutils)
   #:use-module (gnu packages gcc)
@@ -1629,6 +1630,32 @@ (define-public libexpected
     (home-page "https://tl.tartanllama.xyz/")
     (license license:cc0)))
 
+(define-public dwarves
+  (package
+    (name "dwarves")
+    (version "1.24")
+    (source
+     (origin
+       (method git-fetch)
+       (uri (git-reference
+             (url "https://github.com/acmel/dwarves")
+             (commit (string-append "v" version))))
+       (file-name (git-file-name name version))
+       (sha256
+        (base32 "132ln21xj2xhpj3zzpisl18r189jdz0gn6j5rddz2ifp6zlq2vkx"))))
+    (build-system cmake-build-system)
+    (arguments
+     (list
+      #:tests? #f
+      #:configure-flags #~(list "-DLIBBPF_EMBEDDED=OFF" "-D__LIB=lib")))
+    (inputs (list pkg-config zlib libbpf-1.1.0 linux-libre-headers-6.6
+                  elfutils))
+    (home-page "https://github.com/acmel/dwarves")
+    (synopsis "Pahole and the dwarves")
+    (description
+     "pahole - Shows, manipulates data structure layout and pretty prints raw data.")
+    (license license:gpl2)))
+
 (define-public immer
   (package
    (name "immer")
-- 
2.41.0

>From d8322b660c45b4f463106c14a4a4cf15820934cf Mon Sep 17 00:00:00 2001
Message-ID: <[email-masked]>
In-Reply-To: <[email-masked]>
References: <[email-masked]>
From: Brennan Vincent <[email-masked]>
Date: Sat, 24 Feb 2024 10:07:51 -0500
Subject: [PATCH 3/3] gnu: Set CONFIG_DEBUG_INFO_BTF in bpf kernel.

* gnu/packages/linux.scm (linux-libre-with-bpf): Set CONFIG_DEBUG_INFO_BTF.

Change-Id: I9cc0da5394a63ede4a2549cbdcc13b75c8af3001
---
 gnu/packages/linux.scm | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/gnu/packages/linux.scm b/gnu/packages/linux.scm
index 8c665d436d..f894c6cfe3 100644
--- a/gnu/packages/linux.scm
+++ b/gnu/packages/linux.scm
@@ -117,6 +117,7 @@ (define-module (gnu packages linux)
   #:use-module (gnu packages crypto)
   #:use-module (gnu packages cryptsetup)
   #:use-module (gnu packages compression)
+  #:use-module (gnu packages cpp)
   #:use-module (gnu packages databases)
   #:use-module (gnu packages datastructures)
   #:use-module (gnu packages dbm)
@@ -891,7 +892,11 @@ (define %bpf-extra-linux-options
     ;; optional, for kprobes
     ("CONFIG_BPF_EVENTS" . #t)
     ;; kheaders module
-    ("CONFIG_IKHEADERS" . #t)))
+    ("CONFIG_IKHEADERS" . #t)
+    ;; BTF debug info, requires `pahole' from `dwarves' package
+    ("CONFIG_DEBUG_INFO=y" . #t)
+    ("CONFIG_DEBUG_INFO_DWARF4" . #t)
+    ("CONFIG_DEBUG_INFO_BTF" . #t)))
 
 (define (config->string options)
   (string-join (map (match-lambda
@@ -1342,7 +1347,8 @@ (define-public linux-libre-with-bpf
     (package
       (inherit base-linux-libre)
       (inputs (modify-inputs (package-inputs base-linux-libre)
-                (prepend cpio)))
+                (prepend cpio
+                         (@ (gnu packages compression) zlib) python dwarves)))
       (synopsis "Linux-libre with BPF support")
       (description "This package provides GNU Linux-Libre with support
 for @acronym{BPF, the Berkeley Packet Filter}."))))
-- 
2.41.0