labs/sysdev-system-integration: fix perf build with Linux 6.12

Linux 6.12 causes a regression in the perf build, which Luca Ceresoli
has reported upstream at:

  https://lore.kernel.org/all/20241125182506.38af9907@booty/

In the mean time, let's revert the problematic commit.

Signed-off-by: Thomas Petazzoni <[email protected]>

lab-data/embedded-linux/integration/data/0002-Revert-perf-tools-Create-source-symlink-in-perf-obje.patch

@@ -0,0 +1,28 @@
+From df2ce6bb15e0e1fde2196842383ec3d2f1080eab Mon Sep 17 00:00:00 2001
+From: Thomas Petazzoni <[email protected]>
+Date: Sat, 30 Nov 2024 22:05:23 +0100
+Subject: [PATCH] Revert "perf tools: Create source symlink in perf object dir"
+
+This reverts commit 890a1961c812db801e0f9dfaa4af233aa3c6ab63.
+
+Signed-off-by: Thomas Petazzoni <[email protected]>
+---
+ tools/perf/Makefile.perf | 2 --
+ 1 file changed, 2 deletions(-)
+
+diff --git a/tools/perf/Makefile.perf b/tools/perf/Makefile.perf
+index 9dd2e8d3f3c9b..f00f144ddafd2 100644
+--- a/tools/perf/Makefile.perf
++++ b/tools/perf/Makefile.perf
+@@ -163,8 +163,6 @@ ifneq ($(OUTPUT),)
+ # for flex/bison parsers.
+ VPATH += $(OUTPUT)
+ export VPATH
+-# create symlink to the original source
+-SOURCE := $(shell ln -sf $(srctree)/tools/perf $(OUTPUT)/source)
+ endif
+
+ ifeq ($(V),1)
+-- 
+2.47.0
+

labs/sysdev-system-integration/sysdev-system-integration.tex

@@ -34,6 +34,21 @@ \section{Setup}
 git am ../data/0001-package-systemd-fix-bcachefs-magic-patch.patch
 \end{bashinput}
 
+In addition, in the next lab, we're going to use the {\em perf}
+debugging utility which is provided within the Linux kernel source
+code, and unfortunately, the current stable v6.12.x have a regression
+that prevents from building {\em perf} correct. To address this, we
+need to apply a Linux kernel patch, so let's copy this patch to
+\code{board/bootlin/training/}, alongside our already existing Linux
+kernel patch:
+
+\begin{bashinput}
+cp ../data/0002-Revert-perf-tools-Create-source-symlink-in-perf-obje.patch board/bootlin/training
+\end{bashinput}
+
+In one of the next steps, we're going to tell Buildroot apply this
+patch when it will build the Linux kernel.
+
 \section{Root filesystem overlay}
 
 Remove \code{etc/init.d/} from the root filesystem overlay.
@@ -80,7 +95,7 @@ \section{Buildroot configuration}
   \item Set \code{Kernel version} to your kernel version. You can use \code{make kernelversion} to
   get it from the Linux kernel source tree.
   \fi
-  \item Set \code{Custom kernel patches} to \code{board/bootlin/training/0001-Custom-DTS-for-Bootlin-lab.patch}
+  \item Set \code{Custom kernel patches} to \code{board/bootlin/training/0001-Custom-DTS-for-Bootlin-lab.patch} \code{board/bootlin/training/0002-Revert-perf-tools-Create-source-symlink-in-perf-obje.patch}
   \item Set \code{Kernel configuration} to \code{Using a custom (def)config file})
   \item Set \code{Configuration file path} to \code{board/bootlin/training/linux.config}
   \item Select \code{Build a Device Tree Blob (DTB)}