Re: [PATCH v2] x86: fix early boot crash on gcc-10

[Jakub Jelinek]

On Fri, Apr 17, 2020 at 11:22:25AM -0700, Nick Desaulniers wrote:
> > Sorry, I don't quite follow.  The idea is that an empty asm statement
> > in foo() should prevent foo() from being inlined into bar()?
> 
> s/inlined/tail called/

Yeah.  The thing is, the caller changes the stack protector guard base
value, so at the start of the function it saves a different value then
it compares at the end.  But, the function that it calls at the end
actually doesn't return, so this isn't a problem.
If it is tail called though, the stack protector guard checking is done
before the tail call and it crashes.
If the called function is marked with noreturn attribute or _Noreturn,
at least GCC will also not tail call it and all is fine, but not sure
what LLVM does in that case.

	Jakub