Re: [PATCH v40 19/24] x86/vdso: Implement a vDSO for Intel SGX enclave call

[Dave Hansen]

On 11/8/20 12:20 PM, Jethro Beekman wrote:
>> The vDSO function calling convention uses the standard RDI RSI, RDX, RCX,
>> R8 and R9 registers.  This makes it possible to declare the vDSO as a C
>> prototype, but other than that there is no specific support for SystemV
>> ABI. Things like storing XSAVE are the responsibility of the enclave and
>> the runtime.
> I suppose this may be covered under "no specific support for SystemV
> ABI" but with sgx_enclave_run.user_handler=NULL, R12~R15 *will* get
> clobbered when __vdso_sgx_enter_enclave returns from an SGX AEX. IMO
> this makes the whole "try to be like System V ABI" rather useless,
> but I suppose it doesn't matter too much.

What?

It *says*: "there is no specific support for SystemV ABI."  That's the
point.  It's a tiny *PART* of the ABI, used to "make it possible to
declare the vDSO as a C prototype".

That's far from useless.