In case anybody needs some context for this: GCC (and clang) supports an extension to C which allows you to use little bits of assembly within C source files. Linux makes fairly extensive use of this feature for low-level stuff.

The compiler makes various optimisation in the course of building the kernel. For example, it keeps data in the CPU's registers wherever possible, so a lot of the time, using a variable in the source doesn't actually cause a read from main memory at runtime.

Inline assembly introduces code that the compiler didn't generate and does not understand. As such, a block of assembly is required to declare everything that it might have touched, so the compiler can make sure it doesn't make assumptions like "register X contains the same data as memory location Y", if those assumptions might not be true.

This commit removes the flag warning the compiler that the asm might have changed something in memory from a couple of functions which do not, in fact, mess with memory.