On Thu, Jun 5, 2025 at 7:32 AM Jiri Slaby [off-list ref] wrote:

Cc BPF people, just so you know.

On 05. 06. 25, 16:27, Jiri Slaby wrote:

quoted

On 27. 01. 25, 17:05, Uros Bizjak wrote:

quoted

This patch declares percpu variables in __seg_gs/__seg_fs named AS
and keeps them named AS qualified until they are dereferenced with
percpu accessor. This approach enables various compiler check
for cross-namespace variable assignments.

Signed-off-by: Uros Bizjak <redacted>
Acked-by: Nadav Amit <redacted>
Cc: Dennis Zhou <dennis@kernel.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Christoph Lameter <redacted>
Cc: Thomas Gleixner <redacted>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Brian Gerst <redacted>
Cc: Peter Zijlstra <peterz@infradead.org>
---
  arch/x86/include/asm/percpu.h | 15 ++++++++++++---
  1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/percpu.h b/arch/x86/include/asm/

percpu.h
index 27f668660abe..474d648bca9a 100644

--- a/arch/x86/include/asm/percpu.h
+++ b/arch/x86/include/asm/percpu.h

@@ -95,9 +95,18 @@
  #endif /* CONFIG_SMP */
-#define __my_cpu_type(var)    typeof(var) __percpu_seg_override
-#define __my_cpu_ptr(ptr)    (__my_cpu_type(*(ptr))*)(__force

uintptr_t)(ptr)
-#define __my_cpu_var(var)    (*__my_cpu_ptr(&(var)))
+#if defined(CONFIG_USE_X86_SEG_SUPPORT) && defined(USE_TYPEOF_UNQUAL)
+# define __my_cpu_type(var)    typeof(var)
+# define __my_cpu_ptr(ptr)    (ptr)
+# define __my_cpu_var(var)    (var)
+
+# define __percpu_qual        __percpu_seg_override
+#else
+# define __my_cpu_type(var)    typeof(var) __percpu_seg_override
+# define __my_cpu_ptr(ptr)    (__my_cpu_type(*(ptr))*)(__force
uintptr_t)(ptr)
+# define __my_cpu_var(var)    (*__my_cpu_ptr(&(var)))
+#endif
+

Another issue with this is this causes all modules in 6.15 are 2-4 times
(compressed size) bigger:
$ ll /usr/lib/modules/*-[0-9]-default/kernel/drivers/atm/atmtcp.ko.zst
 > -rw-r--r--. 1 root root 10325 May 13 11:49 /usr/lib/modules/6.14.6-2-
default/kernel/drivers/atm/atmtcp.ko.zst
 > -rw-r--r--. 1 root root 39677 Jun  2 09:13 /usr/lib/modules/6.15.0-1-
default/kernel/drivers/atm/atmtcp.ko.zst

It's due to larger .BTF section:
.BTF              PROGBITS         0000000000000000  [-00003080-]
[-       00000000000011a8-]  {+00003100+}
{+       0000000000012cf8+}  0000000000000000           0     0     1

There are a lot of new BTF types defined in each module like:
+attribute_group STRUCT
+backing_dev_info STRUCT
+bdi_writeback STRUCT
+bin_attribute STRUCT
+bio_end_io_t TYPEDEF
+bio_list STRUCT
+bio_set STRUCT
+bio STRUCT
+bio_vec STRUCT

Reverting this gives me back to normal sizes.

Any ideas?

Try newer pahole ?
It was fixed by:
https://lore.kernel.org/bpf/20250429161042.2069678-1-alan.maguire@oracle.com/ (local)