sched, vmlinux.lds: Increase STRUCT_ALIGNMENT to 64 bytes for GCC-4.9

For some mysterious reason GCC-4.9 has a 64 byte section alignment for
structures, all other GCC versions (and Clang) tested (including 4.8
and 5.0) are fine with the 32 bytes alignment.

Getting this right is important for the new SCHED_DATA macro that
creates an explicitly ordered array of 'struct sched_class' in the
linker script and expect pointer arithmetic to work.

Fixes: c3a340f7e7ea ("sched: Have sched_class_highest define by vmlinux.lds.h")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200630144905.GX4817@hirez.programming.kicks-ass.net

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 66fb84c3dc7eef26124b8e9f1b40f64b21cb4334..3ceb4b7279ec2322cff2e0ba3ecdc1eae6b42686 100644 (file)
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -108,6 +108,17 @@
 #define SBSS_MAIN .sbss
 #endif
 
+/*
+ * GCC 4.5 and later have a 32 bytes section alignment for structures.
+ * Except GCC 4.9, that feels the need to align on 64 bytes.
+ */
+#if __GNUC__ == 4 && __GNUC_MINOR__ == 9
+#define STRUCT_ALIGNMENT 64
+#else
+#define STRUCT_ALIGNMENT 32
+#endif
+#define STRUCT_ALIGN() . = ALIGN(STRUCT_ALIGNMENT)
+
 /*
  * The order of the sched class addresses are important, as they are
  * used to determine the order of the priority of each sched class in
@@ -123,13 +134,6 @@
        *(__stop_sched_class)                   \
        __end_sched_classes = .;
 
-/*
- * Align to a 32 byte boundary equal to the
- * alignment gcc 4.5 uses for a struct
- */
-#define STRUCT_ALIGNMENT 32
-#define STRUCT_ALIGN() . = ALIGN(STRUCT_ALIGNMENT)
-
 /* The actual configuration determine if the init/exit sections
  * are handled as text/data or they can be discarded (which
  * often happens at runtime)

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 5aa6661ecaf15e32b395afbb6ae5287621f41c53..9bef2dd01247d85e67b757c19b970fccb9f9b6a8 100644 (file)
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -67,6 +67,7 @@
 #include <linux/tsacct_kern.h>
 
 #include <asm/tlb.h>
+#include <asm-generic/vmlinux.lds.h>
 
 #ifdef CONFIG_PARAVIRT
 # include <asm/paravirt.h>
@@ -1810,7 +1811,7 @@ struct sched_class {
 #ifdef CONFIG_FAIR_GROUP_SCHED
        void (*task_change_group)(struct task_struct *p, int type);
 #endif
-} __aligned(32); /* STRUCT_ALIGN(), vmlinux.lds.h */
+} __aligned(STRUCT_ALIGNMENT); /* STRUCT_ALIGN(), vmlinux.lds.h */
 
 static inline void put_prev_task(struct rq *rq, struct task_struct *prev)
 {