[PATCH] x86/fpu, bug.h: Move CHECK_MEMBER_AT_END_OF() to a generic header and use it in generic code

Ingo Molnar
2015-07-17T08:43:42Z

* Ingo Molnar <mingo@kernel.org> wrote:

>
> * Peter Zijlstra <peterz@infradead.org> wrote:
>
> > On Thu, Jul 16, 2015 at 12:14:37PM -0700, Dave Hansen wrote:
> > > +++ b/arch/x86/kernel/fpu/init.c 2015-07-16 12:02:15.284280976 -0700
> > > @@ -136,6 +136,45 @@ static void __init fpu__init_system_gene
> > > unsigned int xstate_size;
> > > EXPORT_SYMBOL_GPL(xstate_size);
> > >
> > > +#define CHECK_MEMBER_AT_END_OF(TYPE, MEMBER) \
> > > + BUILD_BUG_ON((sizeof(TYPE) - \
> > > + offsetof(TYPE, MEMBER) - \
> > > + sizeof(((TYPE *)0)->MEMBER)) > \
> > > + 0) \
> > > +
> > > +/*
> > > + * We append the 'struct fpu' to the task_struct.
> > > + */
> > > +int __weak arch_task_struct_size(void)
> > > +{
> > > + int task_size = sizeof(struct task_struct);
> > > +
> > > + /*
> > > + * Subtract off the static size of the register state.
> > > + * It potentially has a bunch of padding.
> > > + */
> > > + task_size -= sizeof(((struct task_struct *)0)->thread.fpu.state);
> > > +
> > > + /*
> > > + * Add back the dynamically-calculated register state
> > > + * size.
> > > + */
> > > + task_size += xstate_size;
> > > +
> > > + /*
> > > + * We dynamically size 'struct fpu', so we require that
> > > + * it be at the end of 'thread_struct' and that
> > > + * 'thread_struct' be at the end of 'task_struct'. If
> > > + * you hit a compile error here, check the structure to
> > > + * see if something got added to the end.
> > > + */
> > > + CHECK_MEMBER_AT_END_OF(struct fpu, state);
> > > + CHECK_MEMBER_AT_END_OF(struct thread_struct, fpu);
> > > + CHECK_MEMBER_AT_END_OF(struct task_struct, thread);
> > > +
> > > + return task_size;
> > > +}
> >
> > Since you want these invariants true at all times, maybe put the
> > BUILD_BUG_ON() in generic code instead of x86 specific? That way people
> > poking at other archs are less likely to accidentally break your stuff.
>
> Yeah.

The patch below implements this. Only build tested.

Thanks,

Ingo

===============>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
arch/x86/kernel/fpu/init.c | 17 ++---------------
include/linux/bug.h | 4 ++++
kernel/fork.c | 18 ++++++++++++++++++
3 files changed, 24 insertions(+), 15 deletions(-)

Index: tip/arch/x86/kernel/fpu/init.c
===================================================================
--- tip.orig/arch/x86/kernel/fpu/init.c
+++ tip/arch/x86/kernel/fpu/init.c
@@ -136,16 +136,10 @@ static void __init fpu__init_system_gene
unsigned int xstate_size;
EXPORT_SYMBOL_GPL(xstate_size);

-#define CHECK_MEMBER_AT_END_OF(TYPE, MEMBER) \
- BUILD_BUG_ON((sizeof(TYPE) - \
- offsetof(TYPE, MEMBER) - \
- sizeof(((TYPE *)0)->MEMBER)) > \
- 0) \
-
/*
* We append the 'struct fpu' to the task_struct.
*/
-int __weak arch_task_struct_size(void)
+int arch_task_struct_size(void)
{
int task_size = sizeof(struct task_struct);

@@ -161,16 +155,9 @@ int __weak arch_task_struct_size(void)
*/
task_size += xstate_size;

- /*
- * We dynamically size 'struct fpu', so we require that
- * it be at the end of 'thread_struct' and that
- * 'thread_struct' be at the end of 'task_struct'. If
- * you hit a compile error here, check the structure to
- * see if something got added to the end.
- */
+ /* Build time FPU structure layout debug checks: */
CHECK_MEMBER_AT_END_OF(struct fpu, state);
CHECK_MEMBER_AT_END_OF(struct thread_struct, fpu);
- CHECK_MEMBER_AT_END_OF(struct task_struct, thread);

return task_size;
}
Index: tip/include/linux/bug.h
===================================================================
--- tip.orig/include/linux/bug.h
+++ tip/include/linux/bug.h
@@ -85,6 +85,10 @@ struct pt_regs;

#endif /* __CHECKER__ */

+/* Enforce that 'MEMBER' is the last field of 'TYPE': */
+#define CHECK_MEMBER_AT_END_OF(TYPE, MEMBER) \
+ BUILD_BUG_ON(sizeof(TYPE) != offsetofend(TYPE, MEMBER))
+
#ifdef CONFIG_GENERIC_BUG
#include <asm-generic/bug.h>

Index: tip/kernel/fork.c
===================================================================
--- tip.orig/kernel/fork.c
+++ tip/kernel/fork.c
@@ -287,8 +287,26 @@ static void set_max_threads(unsigned int
max_threads = clamp_t(u64, threads, MIN_THREADS, MAX_THREADS);
}

+#define CHECK_MEMBER_AT_END_OF(TYPE, MEMBER) \
+ BUILD_BUG_ON(sizeof(TYPE) != offsetofend(TYPE, MEMBER))
+
+/*
+ * This function can be overridden by the architecture to support dynamic sizing
+ * of the task_struct:
+ */
int __weak arch_task_struct_size(void)
{
+ /*
+ * Build-time checks for structure layout constraints:
+ *
+ * On some architectures we dynamically size 'struct thread_struct',
+ * so we require that it be at the end of 'task_struct'.
+ *
+ * If you hit a compile error here, check the structure to
+ * see if something got added to the end.
+ */
+ CHECK_MEMBER_AT_END_OF(struct task_struct, thread);
+
return sizeof(struct task_struct);
}