[Bug target/81708] The x86 stack canary location should be customizable

[luto at kernel dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81708

--- Comment #7 from Andy Lutomirski <luto at kernel dot org> ---
Hmm.  This is a big improvement, but it's still going to be awkward to use --
if we want to use a normal Linux percpu variable, we're stuck putting it in a
fixed location that's known at compile time as opposed to just at link time. 
It also still prevents Linux from switching to PC-relative percpu addressing to
reduce text size.

Can we do -mstack-protector-offset=[symbol name]?  And could it be extended to
ask for PC-relative addressing?