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overflow: add DEFINE_FLEX() for on-stack allocs

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Add DEFINE_FLEX() macro for on-stack allocations of structs with
flexible array member.

Expose __struct_size() macro outside of fortify-string.h, as it could be
used to read size of structs allocated by DEFINE_FLEX().
Move __member_size() alongside it.
-Kees

Using underlying array for on-stack storage lets us to declare
known-at-compile-time structures without kzalloc().

Actual usage for ice driver is in following patches of the series.

Missing __has_builtin() workaround is moved up to serve also assembly
compilation with m68k-linux-gcc, see [1].
Error was (note the .S file extension):
In file included from ../include/linux/linkage.h:5,
                 from ../arch/m68k/fpsp040/skeleton.S:40:
../include/linux/compiler_types.h:331:5: warning: "__has_builtin" is not defined, evaluates to 0 [-Wundef]
  331 | #if __has_builtin(__builtin_dynamic_object_size)
      |     ^~~~~~~~~~~~~
../include/linux/compiler_types.h:331:18: error: missing binary operator before token "("
  331 | #if __has_builtin(__builtin_dynamic_object_size)
      |                  ^

[1] https://lore.kernel.org/netdev/202308112122.OuF0YZqL-lkp@intel.com/
Co-developed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Link: https://lore.kernel.org/r/20230912115937.1645707-2-przemyslaw.kitszel@intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Przemek Kitszel
2023-09-12 07:59:31 -04:00
committed by Jakub Kicinski
parent e643597346
commit 26dd68d293
3 changed files with 56 additions and 15 deletions
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35
include/linux/overflow.h
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@@ -309,4 +309,39 @@ static inline size_t __must_check size_sub(size_t minuend, size_t subtrahend)
#define struct_size_t(type, member, count) \
struct_size((type *)NULL, member, count)
/**
* _DEFINE_FLEX() - helper macro for DEFINE_FLEX() family.
* Enables caller macro to pass (different) initializer.
*
* @type: structure type name, including "struct" keyword.
* @name: Name for a variable to define.
* @member: Name of the array member.
* @count: Number of elements in the array; must be compile-time const.
* @initializer: initializer expression (could be empty for no init).
*/
#define _DEFINE_FLEX(type, name, member, count, initializer) \
_Static_assert(__builtin_constant_p(count), \
"onstack flex array members require compile-time const count"); \
union { \
u8 bytes[struct_size_t(type, member, count)]; \
type obj; \
} name##_u initializer; \
type *name = (type *)&name##_u
/**
* DEFINE_FLEX() - Define an on-stack instance of structure with a trailing
* flexible array member.
*
* @type: structure type name, including "struct" keyword.
* @name: Name for a variable to define.
* @member: Name of the array member.
* @count: Number of elements in the array; must be compile-time const.
*
* Define a zeroed, on-stack, instance of @type structure with a trailing
* flexible array member.
* Use __struct_size(@name) to get compile-time size of it afterwards.
*/
#define DEFINE_FLEX(type, name, member, count) \
_DEFINE_FLEX(type, name, member, count, = {})
#endif /* __LINUX_OVERFLOW_H */