Comment by ksherlock

[[ ]] attributes were added in C++11 and later C23. There are 7 standard(C32) attributes but GCC has hundreds of them.

https://en.cppreference.com/w/c/language/attributes.html

https://en.cppreference.com/w/cpp/language/attributes.html

https://gcc.gnu.org/onlinedocs/gcc/Attributes.html

https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attribute...