Re: [PATCH v28 21/22] x86/vdso: Implement a vDSO for Intel SGX enclave call

[Sean Christopherson]

On Mon, Mar 16, 2020 at 02:31:36PM +0100, Jethro Beekman wrote:
> Can someone remind me why we're not passing TCS in RBX but on the stack?

I finally remembered why.  It's pulled off the stack and passed into the
exit handler.  I'm pretty sure the vDSO could take it in %rbx and manually
save it on the stack, but I'd rather keep the current behavior so that the
vDSO is callable from C (assuming @leaf is changed to be passed via %rcx).