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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 <linux@weissschuh.net> Link: https://patch.msgid.link/20251029-sysfs-const-attr-prep-v5-3-ea7d745acff4@weissschuh.net Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>