linux-kernel - Re: [PATCH v5 08/13] selftests/sgx: Handle relocations in test enclave

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Date:   Fri, 1 Sep 2023 01:26:08 +0200
From:   Jo Van Bulck <jo.vanbulck@...kuleuven.be>
To:     "Huang, Kai" <kai.huang@...el.com>,
        "linux-sgx@...r.kernel.org" <linux-sgx@...r.kernel.org>,
        "jarkko@...nel.org" <jarkko@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc:     "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH v5 08/13] selftests/sgx: Handle relocations in test
 enclave

On 01.09.23 01:13, Huang, Kai wrote:
>> encl_body:
>>      /* snipped */
>>      lea    encl_op_array(%rip), %rcx
>>      lea    __encl_base(%rip), %rax
>>      add    (%rcx,%rdx,8),%rax
>>      jmp    *%rax
> 
> call *%rax
> 
> ?
> 
>>      ret

Good catch, but this is indeed the code as generated with gcc -Os (for 
readability). It seems the compiler choose a JMP over a CALL (as the 
stack is untouched and the callee can immediately return to the caller).

Somehow, the compiler still emits a RET after the JMP (which is not 
supposed to return here) though. I agree this is unnecessarily confusing 
and can simply remove the RET from the commit message.

Best,
Jo