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    SubjectRe: [PATCH v2 1/2] selftests/sgx: Use rip relative addressing for encl_stack
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    On Wed, 2022-03-30 at 13:05 -0700, Reinette Chatre wrote:
    >
    >
    > 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.

    I see, I need to correct my patch, thanks!

    RBX gives correct results because of the binary organization,
    i.e. TCS's are placed to zero offset and forward, and
    unrelocated symbol is just compiled in as an untranslated
    offset.

    RPI is given correct results but how the semantics work
    right now is incompatible.

    Still, even for kselftest, I would consider a switch
    because that way:

    1. You can layout binary however you wan and things
    won't break.
    2. You can point to any symbol not just stack, if
    ever need.

    I admit it works semantically but it just super
    unrobust.

    BR, Jarkko

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