Re: [PATCH 1/2] [RFC] debugobjects: avoid gcc-16.0.1 section mismatch

["Arnd Bergmann" <arnd@arndb.de>]

On Mon, May 11, 2026, at 09:18, Thomas Gleixner wrote:
> On Mon, May 11 2026 at 08:17, Arnd Bergmann wrote:
>> On Sun, May 10, 2026, at 21:31, Thomas Gleixner wrote:
>>> On Tue, Feb 03 2026 at 17:23, Arnd Bergmann wrote:
>>>> WARNING: modpost: vmlinux: section mismatch in reference: lookup_object_or_alloc.part.0+0x1ac (section: .text) -> is_static_object (section: .init.text)
>>>>
>>>> From what I can tell, the transformation is correct, as this
>>>> is only called when lookup_object_or_alloc() is called from
>>>> debug_objects_selftest(), which is also __init.
>>>
>>> So clearly the compiler is buggy. It creates an __init specific copy of
>>> lookup_object_or_alloc() and then fails to attribute it correctly.
>>
>> I don't see what else the compiler is supposed to do, it has no idea what
>> __init means in the kernel, or what the rules are for calling between
>> that and normal functions. Putting a non-inlined lookup_object_or_alloc()
>> into a special section without an explicit attribute would clearly
>> be a bug.
>
> I agree that the compiler does not know what __init means, but this
> sucks as it leaves an unused copy of lookup_object_or_alloc() around
> after init.
>
> What happens if you mark is_static_object() with 'noinline'?

I've reproduced the issue with the release gcc-16.1.0 build,
and tested marking is_static_object (along with
dummy_tlb_add_page and dummy_tlb_flush from the other
instance) as noinline.

As expected, this avoids the problem as well.

      Arnd

diff --git a/drivers/iommu/io-pgtable-arm-v7s.c b/drivers/iommu/io-pgtable-arm-v7s.c
index 40e33257d3c2..b89dcf167832 100644
--- a/drivers/iommu/io-pgtable-arm-v7s.c
+++ b/drivers/iommu/io-pgtable-arm-v7s.c
@@ -782,16 +782,17 @@ static void __init dummy_tlb_flush_all(void *cookie)
 	WARN_ON(cookie != cfg_cookie);
 }
 
-static void __init dummy_tlb_flush(unsigned long iova, size_t size,
-				   size_t granule, void *cookie)
+static noinline void __init dummy_tlb_flush(unsigned long iova, size_t size,
+					    size_t granule, void *cookie)
 {
 	WARN_ON(cookie != cfg_cookie);
 	WARN_ON(!(size & cfg_cookie->pgsize_bitmap));
 }
 
-static void __init dummy_tlb_add_page(struct iommu_iotlb_gather *gather,
-				      unsigned long iova, size_t granule,
-				      void *cookie)
+static noinline void __init dummy_tlb_add_page(struct iommu_iotlb_gather *gather,
+					       unsigned long iova,
+					       size_t granule,
+					       void *cookie)
 {
 	dummy_tlb_flush(iova, granule, granule, cookie);
 }
diff --git a/lib/debugobjects.c b/lib/debugobjects.c
index 12e2e42e6a31..18253cb03701 100644
--- a/lib/debugobjects.c
+++ b/lib/debugobjects.c
@@ -1212,7 +1212,7 @@ struct self_test {
 
 static __initconst const struct debug_obj_descr descr_type_test;
 
-static bool __init is_static_object(void *addr)
+static noinline bool __init is_static_object(void *addr)
 {
 	struct self_test *obj = addr;