On Fri, Dec 01, 2023 at 03:10:35PM +0100, Uros Bizjak wrote:
> > sparse warnings: (new ones prefixed by >>)
> > kernel/bpf/percpu_freelist.c: note: in included file (through arch/x86/include/asm/preempt.h, include/linux/preempt.h, include/linux/spinlock.h, ...):
> > arch/x86/include/asm/percpu.h:550:49: sparse: sparse: Expected ) at end of cast operator
> > arch/x86/include/asm/percpu.h:550:49: sparse: sparse: got __seg_gs
> > arch/x86/include/asm/percpu.h:564:33: sparse: sparse: Expected ) at end of cast operator
> > arch/x86/include/asm/percpu.h:564:33: sparse: sparse: got __seg_gs
>
> sparse is too strict here. The following code is perfectly legal:
>
It's not that sparse is too strict, it's because it knows nothing about __seg_gs.
What is missing is:
diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
index 547ea1ff806e..9214f6d54e63 100644
--- a/include/linux/compiler_types.h
+++ b/include/linux/compiler_types.h
@@ -23,6 +23,7 @@
# define __iomem __attribute__((noderef, address_space(__iomem)))
# define __percpu __attribute__((noderef, address_space(__percpu)))
# define __rcu __attribute__((noderef, address_space(__rcu)))
+# define __seg_gs __attribute__((noderef, address_space(__seg_gs)))
static inline void __chk_user_ptr(const volatile void __user *ptr) { }
static inline void __chk_io_ptr(const volatile void __iomem *ptr) { }
/* context/locking */
But with this patch sparse will now complain with 'warning: dereference of noderef expression'
which are quite legit given the noderef and the way __seg_gs is used.
You have two choices quiet these:
1) If variables qualified with __seg_gs should only be dereferenced via some
special accessor like __raw_cpu_{read,write}() the patch here above is
correct and you need to fix the typing inside these accessors (using __force or
casting to unsigned long like already done anyway in __my_cpu_ptr()).
I think this is the correct solution.
2) If it's OK to dereference __seg_gs qualified variables anywhere in the code
(I don't think we should), then the 'noderef' in the patch should be removed.
Sorry, I can't currently do any testing or so.
Best regards
-- Luc
