linux-kernel - Re: [PATCH v2 1/2] selftests/sgx: Use rip relative addressing for encl

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Date:   Wed, 30 Mar 2022 13:05:03 -0700
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     Jarkko Sakkinen <jarkko@...nel.org>
CC:     Shuah Khan <skhan@...uxfoundation.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Shuah Khan <shuah@...nel.org>,
        "open list:INTEL SGX" <linux-sgx@...r.kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/2] selftests/sgx: Use rip relative addressing for
 encl_stack



On 3/30/2022 12:03 PM, Jarkko Sakkinen wrote:
> On Wed, 2022-03-30 at 10:40 -0700, Reinette Chatre wrote:
>> Could you please elaborate how the compiler will fix it up?
> 
> Sure.
> 
> Here's the disassembly of the RBX version:
> 
> [0x000021a9]> pi 1
> lea rax, [rbx + loc.encl_stack]
> 
> Here's the same with s/RBX/RIP/:
> 
> [0x000021a9]> pi 5
> lea rax, loc.encl_stack
> 
> Compiler will substitute correct offset relative to the RIP,
> well, because it can and it makes sense.

It does not make sense to me because, as proven with my test,
the two threads end up sharing the same stack memory.

Reinette