linux-kernel - Re: [PATCH V2 01/15] selftests/x86/sgx: Fix a benign linker warning

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Date:   Fri, 29 Oct 2021 10:09:26 -0700
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     Dave Hansen <dave.hansen@...el.com>, <jarkko@...nel.org>,
        <linux-sgx@...r.kernel.org>, <shuah@...nel.org>,
        <dave.hansen@...ux.intel.com>
CC:     <seanjc@...gle.com>, <linux-kselftest@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2 01/15] selftests/x86/sgx: Fix a benign linker warning

Hi Dave,

On 10/28/2021 5:26 PM, Dave Hansen wrote:
> On 10/28/21 1:37 PM, Reinette Chatre wrote:
>> From: Sean Christopherson <sean.j.christopherson@...el.com>
>>
>> Pass a build id of "none" to the linker to suppress a warning about the
>> build id being ignored:
>>
>>    /usr/bin/ld: warning: .note.gnu.build-id section discarded, --build-id
>>    ignored.
> 
> Do we have a good grasp on why this is producing a warning in the first
> place?  This seems like something that could get merged quickly with one
> more sentence in the changelog.
> 

How about a new changelog as below:

The enclave binary (test_encl.elf) is built with only three sections 
(tcs, text, and data) as controlled by its custom linker script.

If gcc is built with "--enable-linker-build-id" (this appears to be a 
common configuration even if it is by default off) then gcc will pass 
"--build-id" to the linker that will prompt it (the linker) to to write 
unique bits identifying the linked file to a ".note.gnu.build-id" section.

The section ".note.gnu.build-id" does not exist in the test enclave 
resulting in the following warning emitted by the linker:

/usr/bin/ld: warning: .note.gnu.build-id section discarded, --build-id 
ignored

The test enclave does not use the build id within the binary so fix the 
warning by passing a build id of "none" to the linker that will disable 
the setting from any earlier "--build-id" options and thus disable the 
attempt to write the build id to a ".note.gnu.build-id" section that 
does not exist.

Reinette