From: Thomas Weißschuh Date: Wed, 29 Oct 2025 08:12:12 +0000 (+0100) Subject: sysfs: introduce __SYSFS_FUNCTION_ALTERNATIVE() X-Git-Tag: v6.19-rc1~90^2~17 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=02ac5335a55111d87a7a618355261b4407ed0f7f;p=thirdparty%2Fkernel%2Flinux.git sysfs: introduce __SYSFS_FUNCTION_ALTERNATIVE() For the constification phase of 'struct attribute' various callback struct members will need to exist in both const and non-const variants. Keeping both members in a union avoids memory and CPU overhead but will be detected and trapped by Control Flow Integrity (CFI). By deciding between a struct and a union depending whether CFI is enabled, most configurations can avoid this overhead. Code using these callbacks will still need to be updated to handle both members explicitly. In the union case the compiler will recognize that testing for one union member is enough and optimize away the code for the other one. Signed-off-by: Thomas Weißschuh Link: https://patch.msgid.link/20251029-sysfs-const-attr-prep-v5-3-ea7d745acff4@weissschuh.net Signed-off-by: Greg Kroah-Hartman --- diff --git a/include/linux/sysfs.h b/include/linux/sysfs.h index 92f82cee5f11e..9cef5bf24ba71 100644 --- a/include/linux/sysfs.h +++ b/include/linux/sysfs.h @@ -58,6 +58,12 @@ do { \ #define sysfs_attr_init(attr) do {} while (0) #endif +#ifdef CONFIG_CFI +#define __SYSFS_FUNCTION_ALTERNATIVE(MEMBERS...) struct { MEMBERS } +#else +#define __SYSFS_FUNCTION_ALTERNATIVE(MEMBERS...) union { MEMBERS } +#endif + /** * struct attribute_group - data structure used to declare an attribute group. * @name: Optional: Attribute group name