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SubjectRe: [sched] c3a340f7e7: invalid_opcode:#[##]
On Tue, Jun 30, 2020 at 04:02:31PM +0200, Peter Zijlstra wrote:
> On Tue, Jun 30, 2020 at 03:55:05PM +0200, Rasmus Villemoes wrote:
>
> > > Consistently so with GCC-4.9. Any other GCC I tried does the sane thing.
> >
> > Does that include gcc 4.8, or is it only "anything newer than 4.9"?
>
> It includes 4.8 :-)
>
> > so the section it was put in has an alignment of 64. The generated
> > assembly is indeed
> >
> > .globl fair_sched_class
> > .section __fair_sched_class,"a",@progbits
> > .align 64
> >
> > /me goes brew coffee
>
> Right.. so I now have the below patch, and with that I get:
>
> 62931: c1e62c20 0 NOTYPE GLOBAL DEFAULT 2 __begin_sched_classes
> 65736: c1e62e40 128 OBJECT GLOBAL DEFAULT 2 stop_sched_class
> 71813: c1e62cc0 128 OBJECT GLOBAL DEFAULT 2 fair_sched_class
> 78689: c1e62c40 128 OBJECT GLOBAL DEFAULT 2 idle_sched_class
> 78953: c1e62ec0 0 NOTYPE GLOBAL DEFAULT 2 __end_sched_classes
> 79090: c1e62d40 128 OBJECT GLOBAL DEFAULT 2 rt_sched_class
> 79431: c1e62dc0 128 OBJECT GLOBAL DEFAULT 2 dl_sched_class
>
>
> Which has me stumped on __begin_sched_classes being on a 32byte edge
> (and crashes differently due to that).
>
> Argh!!

Steve suggested adding a dummy variable before the lot and this actually
works... But this just cannot be right :-(


---
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 66fb84c3dc7ee..9c0ee5cf73a50 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -108,6 +108,17 @@
#define SBSS_MAIN .sbss
#endif

+/*
+ * Align to a 32 byte boundary equal to the
+ * alignment gcc 4.5 uses for a struct
+ */
+#if GCC_VERSION >= 40900 && GCC_VERSION < 50000
+#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
@@ -115,6 +126,7 @@
*/
#define SCHED_DATA \
STRUCT_ALIGN(); \
+ *(__dummy_sched_class) \
__begin_sched_classes = .; \
*(__idle_sched_class) \
*(__fair_sched_class) \
@@ -123,13 +135,6 @@
*(__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/core.c b/kernel/sched/core.c
index 81640fe0eae8f..f8535a3438819 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6641,6 +6641,9 @@ static struct kmem_cache *task_group_cache __read_mostly;
DECLARE_PER_CPU(cpumask_var_t, load_balance_mask);
DECLARE_PER_CPU(cpumask_var_t, select_idle_mask);

+const struct sched_class dummy_sched_class
+ __attribute__((section("__dummy_sched_class")));
+
void __init sched_init(void)
{
unsigned long ptr = 0;
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 4165c06d1d7bd..33251d0ab62e7 100644
--- 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>
@@ -1811,7 +1812,7 @@ 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)
{
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