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Date:   Fri, 25 Sep 2020 14:17:13 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
To:     Jethro Beekman <jethro@fortanix.com>
Cc:     Borislav Petkov <bp@alien8.de>, x86@kernel.org,
        linux-sgx@vger.kernel.org, linux-kernel@vger.kernel.org,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        Andy Lutomirski <luto@amacapital.net>,
        Cedric Xing <cedric.xing@intel.com>, akpm@linux-foundation.org,
        andriy.shevchenko@linux.intel.com, asapek@google.com,
        chenalexchen@google.com, conradparker@google.com,
        cyhanish@google.com, dave.hansen@intel.com, haitao.huang@intel.com,
        josh@joshtriplett.org, kai.huang@intel.com, kai.svahn@intel.com,
        kmoy@google.com, ludloff@google.com, luto@kernel.org,
        nhorman@redhat.com, npmccallum@redhat.com, puiterwijk@redhat.com,
        rientjes@google.com, tglx@linutronix.de, yaozhangx@google.com
Subject: Re: [PATCH v38 21/24] x86/vdso: Implement a vDSO for Intel SGX
 enclave call
Message-ID: <20200925111713.GD180915@linux.intel.com>
References: <20200915112842.897265-1-jarkko.sakkinen@linux.intel.com>
 <20200915112842.897265-22-jarkko.sakkinen@linux.intel.com>
 <20200924180407.GO5030@zn.tnic>
 <20200925010031.GH119995@linux.intel.com>
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On Fri, Sep 25, 2020 at 10:39:58AM +0200, Jethro Beekman wrote:
> On 2020-09-25 03:00, Jarkko Sakkinen wrote:
> > End result:
> > 
> > https://git.kernel.org/pub/scm/linux/kernel/git/jarkko/linux-sgx.git/tree/arch/x86/include/uapi/asm/sgx.h
> > 
> > I'm wondering this sentence:
> > 
> > "The calling convention is custom and does not follow System V x86-64 ABI."
> > 
> > AFAIK, now the vDSO is fully C-callable but waiting for feedback before
> > removing it.
> 
> It's C-callable *iff your enclave follows the System V x86-64 ABI*. In
> addition, all registers not clobbered by the SGX ISA are passed to the
> enclave, not just those specified as parameter passing registers in
> the ABI. This is intentional to make the vDSO function usable in
> applications that use the current flexibility of ENCLU.

Hold on, I really want to fix this bit of documentation before sending
any new version, so I'll explain how I understand it.

I think it is just SystemV ABI call with six parameters in the usual
GPRs (rdi, rsi, rdx, rcx, r8, r9).

I'm looking at vdso_sgx_enter_enclave.

What I'm not getting?

> --
> Jethro Beekman | Fortanix

/Jarkko