fix: sublevel version overflow in LINUX_VERSION_CODE

The 4.4.256 and 4.9.256 stable release overflow the 8bits allocated to
the sublevel in LINUX_VERSION_CODE which ends means they report
themselves as 4.5.0 and 4.10.0 respectively. The next releases in these
stables branches will have sublevel clamped at 255 and will thus report
themselves as 4.4.255 and 4.9.255 for all subsequent releases.

We need a way to way to properly detect these release since I doubt they
will stop breaking tracepoints declarations. As a workaround, extract
the version information from the Makefile in the kernel headers and use
this information to generate a version code when the sublevel is equal
or greater than 256.

Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: Ie12dec7d2f28fc83343262f42680d42a2f40b59e

diff --git a/Kbuild.common b/Kbuild.common
index 09296e7032af804303e8eb8b3cc5dedff72ac3b7..3d165577cee5cd626710c245953b5f375804261d 100644 (file)
--- a/Kbuild.common
+++ b/Kbuild.common
@@ -1,5 +1,9 @@
 # SPDX-License-Identifier: (GPL-2.0 OR LGPL-2.1)
 
+ccflags-y += -DLTTNG_LINUX_MAJOR=$(VERSION)
+ccflags-y += -DLTTNG_LINUX_MINOR=$(PATCHLEVEL)
+ccflags-y += -DLTTNG_LINUX_PATCH=$(SUBLEVEL)
+
 # Work-around for distro-specific public modules ABI breakages.
 # Some distributions break the public module instrumentation ABI
 # compared to upstream stable kernels without providing other mean than

diff --git a/lttng-kernel-version.h b/lttng-kernel-version.h
index daf2c6adcb75ea9650d9c41c521f3083a7882377..806d978ba6debb946af3f47b8703a5b2a9f2f9b2 100644 (file)
--- a/lttng-kernel-version.h
+++ b/lttng-kernel-version.h
@@ -2,7 +2,7 @@
  *
  * lttng-kernel-version.h
  *
- * Contains helpers to check more complex kernel version conditions.
+ * Contains helpers to check kernel version conditions.
  *
  * Copyright (C) 2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
  */
@@ -13,9 +13,49 @@
 #include <linux/version.h>
 #include <generated/utsrelease.h>
 
+/*
+ * The following defines are extracted from the toplevel Linux Makefile and
+ * passed on the command line -with '-D'.
+ */
+
+#ifndef LTTNG_LINUX_MAJOR
+#define LTTNG_LINUX_MAJOR 0
+#endif
+
+#ifndef LTTNG_LINUX_MINOR
+#define LTTNG_LINUX_MINOR 0
+#endif
+
+#ifndef LTTNG_LINUX_PATCH
+#define LTTNG_LINUX_PATCH 0
+#endif
+
+/*
+ * Some stable releases have overflowed the 8bits allocated to the sublevel in
+ * the version code. To determine if the current kernel is affected, use the
+ * sublevel version from the Makefile. This is currently true for the 4.4.256
+ * and 4.9.256 stable releases.
+ *
+ * When the sublevel has overflowed, use the values from the Makefile instead
+ * of LINUX_VERSION_CODE from the kernel headers and allocate 16bits.
+ * Otherwise, keep using the version code from the headers to minimise the
+ * behavior change and avoid regressions.
+ */
+#if (LTTNG_LINUX_PATCH >= 256)
+
+#define LTTNG_KERNEL_VERSION(a, b, c) \
+       (((a) << 24) + ((b) << 16) + (c))
+
+#define LTTNG_LINUX_VERSION_CODE \
+       LTTNG_KERNEL_VERSION(LTTNG_LINUX_MAJOR, LTTNG_LINUX_MINOR, LTTNG_LINUX_PATCH)
+
+#else
+
 #define LTTNG_KERNEL_VERSION(a, b, c) KERNEL_VERSION(a, b, c)
 #define LTTNG_LINUX_VERSION_CODE LINUX_VERSION_CODE
 
+#endif
+
 /*
  * This macro checks if the kernel version is between the two specified
  * versions (lower limit inclusive, upper limit exclusive).