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SubjectRe: [sched] c3a340f7e7: invalid_opcode:#[##]
On Tue, Jun 30, 2020 at 02:46:28PM +0200, Peter Zijlstra wrote:
> On Mon, Jun 29, 2020 at 08:31:27AM +0800, kernel test robot wrote:
> > Greeting,
> >
> > FYI, we noticed the following commit (built with gcc-4.9):
> >
> > commit: c3a340f7e7eadac7662ab104ceb16432e5a4c6b2 ("sched: Have sched_class_highest define by vmlinux.lds.h")
>
> > [ 1.840970] kernel BUG at kernel/sched/core.c:6652!
>
> W T H
>
> $ readelf -Wa defconfig-build/vmlinux | grep sched_class
> 62931: c1e62d20 0 NOTYPE GLOBAL DEFAULT 2 __begin_sched_classes
> 65736: c1e62f40 96 OBJECT GLOBAL DEFAULT 2 stop_sched_class
> 71813: c1e62dc0 96 OBJECT GLOBAL DEFAULT 2 fair_sched_class
> 78689: c1e62d40 96 OBJECT GLOBAL DEFAULT 2 idle_sched_class
> 78953: c1e62fa0 0 NOTYPE GLOBAL DEFAULT 2 __end_sched_classes
> 79090: c1e62e40 96 OBJECT GLOBAL DEFAULT 2 rt_sched_class
> 79431: c1e62ec0 96 OBJECT GLOBAL DEFAULT 2 dl_sched_class
>
> $ printf "%d\n" $((0xc1e62dc0 - 0xc1e62d40))
> 128
>
> So even though the object is 96 bytes in size, has an explicit 32 byte
> alignment, the array ends up with a stride of 128 bytes !?!?!
>
> Consistently so with GCC-4.9. Any other GCC I tried does the sane thing.
>
> Full patch included below.
>
> Anybody any clue wth 4.9 is doing crazy things like this?
>
> ---

This seems to make everything work, it builds and boots for 4.9 and
builds x86_64-defconfig with clang11 (just to check a !GCC compiler).

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 66fb84c3dc7ee..49a9aaa1e2424 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 __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 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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