[PATCH v2 0/3] Switch get/put unaligned to use memcpy

[PATCH v2 0/3] Switch get/put unaligned to use memcpy

[Ian Rogers]

The existing type punning approach with packed structs requires
 -fno-strict-aliasing to be passed to the compiler for
correctness. This is true in the kernel tree but not in the tools
directory resulting in this suggested patch from Eric Biggers
 <ebiggers@google.com>:
https://lore.kernel.org/lkml/20250614044133.660848-2-ebiggers@kernel.org/

Requiring -fno-strict-aliasing seems unfortunate and so this patch
makes the unaligned code work via memcpy for type punning rather than
the packed attribute.

v2: switch memcpy to __builtin_memcpy to avoid potential/disallowed
    memcpy calls in vdso caused by -fno-builtin. Reported by
    Christophe Leroy <christophe.leroy@csgroup.eu>:
    https://lore.kernel.org/lkml/c57de5bf-d55c-48c5-9dfa-e2fb844dafe9@csgroup.eu/

Ian Rogers (3):
  vdso: Switch get/put unaligned from packed struct to memcpy
  tools headers: Update the linux/unaligned.h copy with the kernel
    sources
  tools headers: Remove unneeded ignoring of warnings in unaligned.h

 include/vdso/unaligned.h        | 48 ++++++++++++++++++++++++++++-----
 tools/include/linux/unaligned.h |  4 ---
 tools/include/vdso/unaligned.h  | 48 ++++++++++++++++++++++++++++-----
 3 files changed, 84 insertions(+), 16 deletions(-)

-- 
2.50.0.rc2.701.gf1e915cc24-goog

[PATCH v2 1/3] vdso: Switch get/put unaligned from packed struct to memcpy

[Ian Rogers]

Type punning is necessary for get/put unaligned but the use of a
packed struct violates strict aliasing rules, requiring
-fno-strict-aliasing to be passed to the C compiler. Switch to using
memcpy so that -fno-strict-aliasing isn't necessary.

Signed-off-by: Ian Rogers <irogers@google.com>
---
 include/vdso/unaligned.h | 48 +++++++++++++++++++++++++++++++++++-----
 1 file changed, 42 insertions(+), 6 deletions(-)

diff --git a/include/vdso/unaligned.h b/include/vdso/unaligned.h
index ff0c06b6513e..f33c1eefbf68 100644
--- a/include/vdso/unaligned.h
+++ b/include/vdso/unaligned.h
@@ -2,14 +2,50 @@
 #ifndef __VDSO_UNALIGNED_H
 #define __VDSO_UNALIGNED_H
 
-#define __get_unaligned_t(type, ptr) ({							\
-	const struct { type x; } __packed * __get_pptr = (typeof(__get_pptr))(ptr);	\
-	__get_pptr->x;									\
+#define ____get_unaligned_type(type) type: (type)0
+/**
+ * __get_unaligned_t - read an unaligned value from memory.
+ * @ptr:	the pointer to load from.
+ * @type:	the type to load from the pointer.
+ *
+ * Use memcpy to affect an unaligned type sized load avoiding undefined behavior
+ * from approaches like type punning that require -fno-strict-aliasing in order
+ * to be correct. As type may be const, use _Generic to map to a non-const type
+ * - you can't memcpy into a const type. The void* cast silences ubsan warnings.
+ */
+#define __get_unaligned_t(type, ptr) ({					\
+	type __get_unaligned_map_ctrl = 0;				\
+	typeof(_Generic(__get_unaligned_map_ctrl,			\
+		____get_unaligned_type(short int),			\
+		____get_unaligned_type(unsigned short int),		\
+		____get_unaligned_type(int),				\
+		____get_unaligned_type(unsigned int),			\
+		____get_unaligned_type(long),				\
+		____get_unaligned_type(unsigned long),			\
+		____get_unaligned_type(long long),			\
+		____get_unaligned_type(unsigned long long),		\
+		default: (type)0					\
+		)) __get_unaligned_val;					\
+	(void)__get_unaligned_map_ctrl;					\
+	__builtin_memcpy(&__get_unaligned_val, (void *)(ptr),		\
+			 sizeof(__get_unaligned_val));			\
+	__get_unaligned_val;						\
 })
 
-#define __put_unaligned_t(type, val, ptr) do {						\
-	struct { type x; } __packed * __put_pptr = (typeof(__put_pptr))(ptr);		\
-	__put_pptr->x = (val);								\
+/**
+ * __put_unaligned_t - write an unaligned value to memory.
+ * @type:	the type of the value to store.
+ * @val:	the value to store.
+ * @ptr:	the pointer to store to.
+ *
+ * Use memcpy to affect an unaligned type sized store avoiding undefined
+ * behavior from approaches like type punning that require -fno-strict-aliasing
+ * in order to be correct. The void* cast silences ubsan warnings.
+ */
+#define __put_unaligned_t(type, val, ptr) do {				\
+	type __put_unaligned_val = (val);				\
+	__builtin_memcpy((void *)(ptr), &__put_unaligned_val,		\
+			 sizeof(__put_unaligned_val));			\
 } while (0)
 
 #endif /* __VDSO_UNALIGNED_H */
-- 
2.50.0.rc2.701.gf1e915cc24-goog

Re: [PATCH v2 1/3] vdso: Switch get/put unaligned from packed struct to memcpy

[Christophe Leroy]

Le 17/06/2025 à 22:53, Ian Rogers a écrit :
> Type punning is necessary for get/put unaligned but the use of a
> packed struct violates strict aliasing rules, requiring
> -fno-strict-aliasing to be passed to the C compiler. Switch to using
> memcpy so that -fno-strict-aliasing isn't necessary.
> 
> Signed-off-by: Ian Rogers <irogers@google.com>

Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>



> ---
>   include/vdso/unaligned.h | 48 +++++++++++++++++++++++++++++++++++-----
>   1 file changed, 42 insertions(+), 6 deletions(-)
> 
> diff --git a/include/vdso/unaligned.h b/include/vdso/unaligned.h
> index ff0c06b6513e..f33c1eefbf68 100644
> --- a/include/vdso/unaligned.h
> +++ b/include/vdso/unaligned.h
> @@ -2,14 +2,50 @@
>   #ifndef __VDSO_UNALIGNED_H
>   #define __VDSO_UNALIGNED_H
>   
> -#define __get_unaligned_t(type, ptr) ({							\
> -	const struct { type x; } __packed * __get_pptr = (typeof(__get_pptr))(ptr);	\
> -	__get_pptr->x;									\
> +#define ____get_unaligned_type(type) type: (type)0
> +/**
> + * __get_unaligned_t - read an unaligned value from memory.
> + * @ptr:	the pointer to load from.
> + * @type:	the type to load from the pointer.
> + *
> + * Use memcpy to affect an unaligned type sized load avoiding undefined behavior
> + * from approaches like type punning that require -fno-strict-aliasing in order
> + * to be correct. As type may be const, use _Generic to map to a non-const type
> + * - you can't memcpy into a const type. The void* cast silences ubsan warnings.
> + */
> +#define __get_unaligned_t(type, ptr) ({					\
> +	type __get_unaligned_map_ctrl = 0;				\
> +	typeof(_Generic(__get_unaligned_map_ctrl,			\
> +		____get_unaligned_type(short int),			\
> +		____get_unaligned_type(unsigned short int),		\
> +		____get_unaligned_type(int),				\
> +		____get_unaligned_type(unsigned int),			\
> +		____get_unaligned_type(long),				\
> +		____get_unaligned_type(unsigned long),			\
> +		____get_unaligned_type(long long),			\
> +		____get_unaligned_type(unsigned long long),		\
> +		default: (type)0					\
> +		)) __get_unaligned_val;					\
> +	(void)__get_unaligned_map_ctrl;					\
> +	__builtin_memcpy(&__get_unaligned_val, (void *)(ptr),		\
> +			 sizeof(__get_unaligned_val));			\
> +	__get_unaligned_val;						\
>   })
>   
> -#define __put_unaligned_t(type, val, ptr) do {						\
> -	struct { type x; } __packed * __put_pptr = (typeof(__put_pptr))(ptr);		\
> -	__put_pptr->x = (val);								\
> +/**
> + * __put_unaligned_t - write an unaligned value to memory.
> + * @type:	the type of the value to store.
> + * @val:	the value to store.
> + * @ptr:	the pointer to store to.
> + *
> + * Use memcpy to affect an unaligned type sized store avoiding undefined
> + * behavior from approaches like type punning that require -fno-strict-aliasing
> + * in order to be correct. The void* cast silences ubsan warnings.
> + */
> +#define __put_unaligned_t(type, val, ptr) do {				\
> +	type __put_unaligned_val = (val);				\
> +	__builtin_memcpy((void *)(ptr), &__put_unaligned_val,		\
> +			 sizeof(__put_unaligned_val));			\
>   } while (0)
>   
>   #endif /* __VDSO_UNALIGNED_H */

Re: [PATCH v2 1/3] vdso: Switch get/put unaligned from packed struct to memcpy

[kernel test robot]

Hi Ian,

kernel test robot noticed the following build warnings:

[auto build test WARNING on linus/master]
[also build test WARNING on v6.16-rc2 next-20250618]
[cannot apply to tip/timers/vdso acme/perf/core]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Ian-Rogers/vdso-Switch-get-put-unaligned-from-packed-struct-to-memcpy/20250618-045610
base:   linus/master
patch link:    https://lore.kernel.org/r/20250617205320.1580946-2-irogers%40google.com
patch subject: [PATCH v2 1/3] vdso: Switch get/put unaligned from packed struct to memcpy
config: parisc-allnoconfig (https://download.01.org/0day-ci/archive/20250618/202506182044.OhyWGCSm-lkp@intel.com/config)
compiler: hppa-linux-gcc (GCC) 15.1.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250618/202506182044.OhyWGCSm-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202506182044.OhyWGCSm-lkp@intel.com/

All warnings (new ones prefixed by >>):

   In file included from include/linux/swab.h:5,
                    from include/uapi/linux/byteorder/big_endian.h:14,
                    from include/linux/byteorder/big_endian.h:5,
                    from arch/parisc/include/uapi/asm/byteorder.h:5,
                    from arch/parisc/include/asm/bitops.h:11,
                    from include/linux/bitops.h:67,
                    from include/linux/kernel.h:23,
                    from arch/parisc/include/asm/bug.h:5,
                    from include/linux/bug.h:5,
                    from include/linux/thread_info.h:13,
                    from include/linux/sched.h:14,
                    from include/linux/uaccess.h:9,
                    from arch/parisc/boot/compressed/misc.c:7:
   In function 'get_unaligned_le32',
       inlined from 'decompress_kernel' at arch/parisc/boot/compressed/misc.c:312:16:
>> include/vdso/unaligned.h:30:9: warning: '__builtin_memcpy' reading 4 bytes from a region of size 1 [-Wstringop-overread]
      30 |         __builtin_memcpy(&__get_unaligned_val, (void *)(ptr),           \
         |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      31 |                          sizeof(__get_unaligned_val));                  \
         |                          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   include/uapi/linux/swab.h:120:19: note: in definition of macro '__swab32'
     120 |         __fswab32(x))
         |                   ^
   include/linux/byteorder/generic.h:89:21: note: in expansion of macro '__le32_to_cpu'
      89 | #define le32_to_cpu __le32_to_cpu
         |                     ^~~~~~~~~~~~~
   include/linux/unaligned.h:23:28: note: in expansion of macro '__get_unaligned_t'
      23 |         return le32_to_cpu(__get_unaligned_t(__le32, p));
         |                            ^~~~~~~~~~~~~~~~~
   arch/parisc/boot/compressed/misc.c: In function 'decompress_kernel':
   arch/parisc/boot/compressed/misc.c:29:13: note: source object 'output_len' of size 1
      29 | extern char output_len;
         |             ^~~~~~~~~~


vim +/__builtin_memcpy +30 include/vdso/unaligned.h

     4	
     5	#define ____get_unaligned_type(type) type: (type)0
     6	/**
     7	 * __get_unaligned_t - read an unaligned value from memory.
     8	 * @ptr:	the pointer to load from.
     9	 * @type:	the type to load from the pointer.
    10	 *
    11	 * Use memcpy to affect an unaligned type sized load avoiding undefined behavior
    12	 * from approaches like type punning that require -fno-strict-aliasing in order
    13	 * to be correct. As type may be const, use _Generic to map to a non-const type
    14	 * - you can't memcpy into a const type. The void* cast silences ubsan warnings.
    15	 */
    16	#define __get_unaligned_t(type, ptr) ({					\
    17		type __get_unaligned_map_ctrl = 0;				\
    18		typeof(_Generic(__get_unaligned_map_ctrl,			\
    19			____get_unaligned_type(short int),			\
    20			____get_unaligned_type(unsigned short int),		\
    21			____get_unaligned_type(int),				\
    22			____get_unaligned_type(unsigned int),			\
    23			____get_unaligned_type(long),				\
    24			____get_unaligned_type(unsigned long),			\
    25			____get_unaligned_type(long long),			\
    26			____get_unaligned_type(unsigned long long),		\
    27			default: (type)0					\
    28			)) __get_unaligned_val;					\
    29		(void)__get_unaligned_map_ctrl;					\
  > 30		__builtin_memcpy(&__get_unaligned_val, (void *)(ptr),		\
    31				 sizeof(__get_unaligned_val));			\
    32		__get_unaligned_val;						\
    33	})
    34	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [PATCH v2 1/3] vdso: Switch get/put unaligned from packed struct to memcpy

[David Laight]

On Tue, 17 Jun 2025 13:53:18 -0700
Ian Rogers <irogers@google.com> wrote:

> Type punning is necessary for get/put unaligned but the use of a
> packed struct violates strict aliasing rules, requiring
> -fno-strict-aliasing to be passed to the C compiler. Switch to using
> memcpy so that -fno-strict-aliasing isn't necessary.
>....							\
> +/**
> + * __put_unaligned_t - write an unaligned value to memory.
> + * @type:	the type of the value to store.
> + * @val:	the value to store.
> + * @ptr:	the pointer to store to.
> + *
> + * Use memcpy to affect an unaligned type sized store avoiding undefined
> + * behavior from approaches like type punning that require -fno-strict-aliasing
> + * in order to be correct. The void* cast silences ubsan warnings.
> + */
> +#define __put_unaligned_t(type, val, ptr) do {				\
> +	type __put_unaligned_val = (val);				\
> +	__builtin_memcpy((void *)(ptr), &__put_unaligned_val,		\
> +			 sizeof(__put_unaligned_val));			\
>  } while (0)

Does that actually work?
If 'ptr' has type 'long *' gcc will (validly according to C) assume
it is aligned and will generate a misaligned memory write.
The (void *) cast make no difference.

Using (void *)(long)(ptr) might lose the alignment.
Otherwise you may need to use OPTIMISER_HIDE_VAR() and live
with the extra register-register move it tends to generate.

	David

[PATCH v2 2/3] tools headers: Update the linux/unaligned.h copy with the kernel sources

[Ian Rogers]

To pick up the changes in:

  fe9b2b7b3583 vdso: Switch get/put unaligned from packed struct to memcpy

Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/include/vdso/unaligned.h | 48 +++++++++++++++++++++++++++++-----
 1 file changed, 42 insertions(+), 6 deletions(-)

diff --git a/tools/include/vdso/unaligned.h b/tools/include/vdso/unaligned.h
index ff0c06b6513e..f33c1eefbf68 100644
--- a/tools/include/vdso/unaligned.h
+++ b/tools/include/vdso/unaligned.h
@@ -2,14 +2,50 @@
 #ifndef __VDSO_UNALIGNED_H
 #define __VDSO_UNALIGNED_H
 
-#define __get_unaligned_t(type, ptr) ({							\
-	const struct { type x; } __packed * __get_pptr = (typeof(__get_pptr))(ptr);	\
-	__get_pptr->x;									\
+#define ____get_unaligned_type(type) type: (type)0
+/**
+ * __get_unaligned_t - read an unaligned value from memory.
+ * @ptr:	the pointer to load from.
+ * @type:	the type to load from the pointer.
+ *
+ * Use memcpy to affect an unaligned type sized load avoiding undefined behavior
+ * from approaches like type punning that require -fno-strict-aliasing in order
+ * to be correct. As type may be const, use _Generic to map to a non-const type
+ * - you can't memcpy into a const type. The void* cast silences ubsan warnings.
+ */
+#define __get_unaligned_t(type, ptr) ({					\
+	type __get_unaligned_map_ctrl = 0;				\
+	typeof(_Generic(__get_unaligned_map_ctrl,			\
+		____get_unaligned_type(short int),			\
+		____get_unaligned_type(unsigned short int),		\
+		____get_unaligned_type(int),				\
+		____get_unaligned_type(unsigned int),			\
+		____get_unaligned_type(long),				\
+		____get_unaligned_type(unsigned long),			\
+		____get_unaligned_type(long long),			\
+		____get_unaligned_type(unsigned long long),		\
+		default: (type)0					\
+		)) __get_unaligned_val;					\
+	(void)__get_unaligned_map_ctrl;					\
+	__builtin_memcpy(&__get_unaligned_val, (void *)(ptr),		\
+			 sizeof(__get_unaligned_val));			\
+	__get_unaligned_val;						\
 })
 
-#define __put_unaligned_t(type, val, ptr) do {						\
-	struct { type x; } __packed * __put_pptr = (typeof(__put_pptr))(ptr);		\
-	__put_pptr->x = (val);								\
+/**
+ * __put_unaligned_t - write an unaligned value to memory.
+ * @type:	the type of the value to store.
+ * @val:	the value to store.
+ * @ptr:	the pointer to store to.
+ *
+ * Use memcpy to affect an unaligned type sized store avoiding undefined
+ * behavior from approaches like type punning that require -fno-strict-aliasing
+ * in order to be correct. The void* cast silences ubsan warnings.
+ */
+#define __put_unaligned_t(type, val, ptr) do {				\
+	type __put_unaligned_val = (val);				\
+	__builtin_memcpy((void *)(ptr), &__put_unaligned_val,		\
+			 sizeof(__put_unaligned_val));			\
 } while (0)
 
 #endif /* __VDSO_UNALIGNED_H */
-- 
2.50.0.rc2.701.gf1e915cc24-goog

[PATCH v2 3/3] tools headers: Remove unneeded ignoring of warnings in unaligned.h

[Ian Rogers]

Now the get/put unaligned use memcpy the -Wpacked and -Wattributes
warnings don't need disabling.

Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/include/linux/unaligned.h | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/tools/include/linux/unaligned.h b/tools/include/linux/unaligned.h
index 395a4464fe73..d51ddafed138 100644
--- a/tools/include/linux/unaligned.h
+++ b/tools/include/linux/unaligned.h
@@ -6,9 +6,6 @@
  * This is the most generic implementation of unaligned accesses
  * and should work almost anywhere.
  */
-#pragma GCC diagnostic push
-#pragma GCC diagnostic ignored "-Wpacked"
-#pragma GCC diagnostic ignored "-Wattributes"
 #include <vdso/unaligned.h>
 
 #define get_unaligned(ptr)	__get_unaligned_t(typeof(*(ptr)), (ptr))
@@ -143,6 +140,5 @@ static inline u64 get_unaligned_be48(const void *p)
 {
 	return __get_unaligned_be48(p);
 }
-#pragma GCC diagnostic pop
 
 #endif /* __LINUX_UNALIGNED_H */
-- 
2.50.0.rc2.701.gf1e915cc24-goog

Re: [PATCH v2 0/3] Switch get/put unaligned to use memcpy

[Christophe Leroy]

Le 17/06/2025 à 22:53, Ian Rogers a écrit :
> The existing type punning approach with packed structs requires
>   -fno-strict-aliasing to be passed to the compiler for
> correctness. This is true in the kernel tree but not in the tools
> directory resulting in this suggested patch from Eric Biggers
>   <ebiggers@google.com>:
> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Flkml%2F20250614044133.660848-2-ebiggers%40kernel.org%2F&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7Cf05413010ecc40ad1bdf08ddade1316a%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C638857904894967529%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=29QUBLnUowncZiTH4z74Ec1olUlX0OTYnUNGDvWxX1o%3D&reserved=0
> 
> Requiring -fno-strict-aliasing seems unfortunate and so this patch
> makes the unaligned code work via memcpy for type punning rather than
> the packed attribute.
> 
> v2: switch memcpy to __builtin_memcpy to avoid potential/disallowed
>      memcpy calls in vdso caused by -fno-builtin. Reported by
>      Christophe Leroy <christophe.leroy@csgroup.eu>:
>      https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Flkml%2Fc57de5bf-d55c-48c5-9dfa-e2fb844dafe9%40csgroup.eu%2F&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7Cf05413010ecc40ad1bdf08ddade1316a%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C638857904894985987%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=l1LJP3XPKVuhDpiHxxkfWBiNPMYaBT9YXGBFzs6wLpY%3D&reserved=0
> 

Does this new version also fixes the failures reported by the robots:
- arm64-randconfig with clang 21
- i386-randconfig with gcc 12

Christophe

> Ian Rogers (3):
>    vdso: Switch get/put unaligned from packed struct to memcpy
>    tools headers: Update the linux/unaligned.h copy with the kernel
>      sources
>    tools headers: Remove unneeded ignoring of warnings in unaligned.h
> 
>   include/vdso/unaligned.h        | 48 ++++++++++++++++++++++++++++-----
>   tools/include/linux/unaligned.h |  4 ---
>   tools/include/vdso/unaligned.h  | 48 ++++++++++++++++++++++++++++-----
>   3 files changed, 84 insertions(+), 16 deletions(-)
> 

Re: [PATCH v2 0/3] Switch get/put unaligned to use memcpy

[Ian Rogers]

On Wed, Jun 18, 2025 at 4:42 AM Christophe Leroy
<christophe.leroy@csgroup.eu> wrote:
>
>
>
> Le 17/06/2025 à 22:53, Ian Rogers a écrit :
> > The existing type punning approach with packed structs requires
> >   -fno-strict-aliasing to be passed to the compiler for
> > correctness. This is true in the kernel tree but not in the tools
> > directory resulting in this suggested patch from Eric Biggers
> >   <ebiggers@google.com>:
> > https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Flkml%2F20250614044133.660848-2-ebiggers%40kernel.org%2F&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7Cf05413010ecc40ad1bdf08ddade1316a%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C638857904894967529%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=29QUBLnUowncZiTH4z74Ec1olUlX0OTYnUNGDvWxX1o%3D&reserved=0
> >
> > Requiring -fno-strict-aliasing seems unfortunate and so this patch
> > makes the unaligned code work via memcpy for type punning rather than
> > the packed attribute.
> >
> > v2: switch memcpy to __builtin_memcpy to avoid potential/disallowed
> >      memcpy calls in vdso caused by -fno-builtin. Reported by
> >      Christophe Leroy <christophe.leroy@csgroup.eu>:
> >      https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Flkml%2Fc57de5bf-d55c-48c5-9dfa-e2fb844dafe9%40csgroup.eu%2F&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7Cf05413010ecc40ad1bdf08ddade1316a%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C638857904894985987%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=l1LJP3XPKVuhDpiHxxkfWBiNPMYaBT9YXGBFzs6wLpY%3D&reserved=0
> >

So I think I can remove the _Generic block in unaligned.h by depending
on the equivalent __unqual_scalar_typeof from
include/linux/compiler_types.h. I think this is preferable and so I'll
post a v3.

> Does this new version also fixes the failures reported by the robots:
> - arm64-randconfig with clang 21

The issue here was:

  llvm-readelf: warning: 'arch/arm64/kernel/vdso/vdso.so.dbg': invalid
PT_DYNAMIC size (0x118)
  llvm-readelf: warning: 'arch/arm64/kernel/vdso/vdso.so.dbg':
PT_DYNAMIC dynamic table is invalid: SHT_DYNAMIC will be used

which the switch to __builtin_memcpy should have resolved.

> - i386-randconfig with gcc 12

The reported error is in the unaligned code from sparse:

   drivers/scsi/megaraid/megaraid_sas_base.c:8438:32: sparse: sparse:
Using plain integer as NULL pointer

I believe this is because of the _Generic block with a pointer type,
and so the use of __unqual_scalar_typeof in the next/v3 patch set
should hopefully resolve it - or else we'll need to special case
pointer types to assign NULL rather than 0, but I'd prefer not to
special case every potential pointer type.

Thanks,
Ian

> Christophe
>
> > Ian Rogers (3):
> >    vdso: Switch get/put unaligned from packed struct to memcpy
> >    tools headers: Update the linux/unaligned.h copy with the kernel
> >      sources
> >    tools headers: Remove unneeded ignoring of warnings in unaligned.h
> >
> >   include/vdso/unaligned.h        | 48 ++++++++++++++++++++++++++++-----
> >   tools/include/linux/unaligned.h |  4 ---
> >   tools/include/vdso/unaligned.h  | 48 ++++++++++++++++++++++++++++-----
> >   3 files changed, 84 insertions(+), 16 deletions(-)
> >
>