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Re: [PATCH] PR ld/19636: [x86] Resolve undefweak and defined symbols in executable
- From: "H.J. Lu" <hjl dot tools at gmail dot com>
- To: Jiong Wang <jiong dot wang at foss dot arm dot com>
- Cc: Kyrill Tkachov <kyrylo dot tkachov at foss dot arm dot com>, Michael Matz <matz at suse dot de>, Cary Coutant <ccoutant at gmail dot com>, Binutils <binutils at sourceware dot org>
- Date: Wed, 2 Mar 2016 04:22:00 -0800
- Subject: Re: [PATCH] PR ld/19636: [x86] Resolve undefweak and defined symbols in executable
- Authentication-results: sourceware.org; auth=none
- References: <20160223175814 dot GA2858 at intel dot com> <alpine dot LSU dot 2 dot 20 dot 1602241552020 dot 20277 at wotan dot suse dot de> <CAMe9rOpEWKVVP=-o0t0emkjKR0-xqnn-YZ5C5nfa=0E4BkEZaw at mail dot gmail dot com> <alpine dot LSU dot 2 dot 20 dot 1602241709410 dot 20277 at wotan dot suse dot de> <CAMe9rOr5qa_PBJA3oDENWErRfrojtzC1ncXaWwyh-1EAczPn-g at mail dot gmail dot com> <alpine dot LSU dot 2 dot 20 dot 1602241749340 dot 20277 at wotan dot suse dot de> <CAMe9rOrSNYV_x-5aU7K+hXHNrinE9Co8y1F5VUkY+SoRQize=g at mail dot gmail dot com> <alpine dot LSU dot 2 dot 20 dot 1602241753490 dot 20277 at wotan dot suse dot de> <CAMe9rOpZNHtKRvx+5QurEOcVU96WEQuBRPJ6UorocjE-8Jd+vQ at mail dot gmail dot com> <alpine dot LSU dot 2 dot 20 dot 1602241808400 dot 20277 at wotan dot suse dot de> <CAMe9rOpAkC238Gvji0rf1_wBqEAZDDeTkhp_o-BirUrTa622aA at mail dot gmail dot com> <alpine dot LSU dot 2 dot 20 dot 1602241843180 dot 20277 at wotan dot suse dot de> <CAJimCsG=1u_yM6SBFAxCxB4JvWtxO5fZ22+OmG6UC_RYON3DdA at mail dot gmail dot com> <alpine dot LSU dot 2 dot 20 dot 1602251356320 dot 20277 at wotan dot suse dot de> <CAMe9rOpzw08UPTfjFEhixY=x4je--03ZdsXdrpdS-2sYSxDE3Q at mail dot gmail dot com> <56D5A0D9 dot 5070500 at foss dot arm dot com> <CAMe9rOq_sXd9qccTddvMB8sTBgOPWq0wgiqSQX4iSyUVys4n-Q at mail dot gmail dot com> <56D6D676 dot 5020202 at foss dot arm dot com>
On Wed, Mar 2, 2016 at 4:03 AM, Jiong Wang <jiong.wang@foss.arm.com> wrote:
>
>
> On 01/03/16 14:37, H.J. Lu wrote:
>>
>> On Tue, Mar 1, 2016 at 6:02 AM, Kyrill Tkachov
>> <kyrylo.tkachov@foss.arm.com> wrote:
>>>
>>> Hi HJ,
>>>
>>> On 26/02/16 12:51, H.J. Lu wrote:
>>>>
>>>> On Thu, Feb 25, 2016 at 10:59 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
>>>>>
>>>>> Here is the updated patch I am testing. The linker behavior is changed
>>>>> in 2 cases when creating executable:
>>>>>
>>>>> 1. When there are mixed PIC and non-PIC references to undefined
>>>>> weak symbols, undefined weak symbols are resolved to 0 at link-time.
>>>>> 2. If all references to undefined weak symbols are PIC, dynamic
>>>>> relocations against undefined weak symbols will be generated unless
>>>>> -z nodynamic-undefined-weak is passed to linker.
>>>>>
>>>>> BTW, We have to resolve R_X86_64_32/R_X86_64_PC32 relocations
>>>>> against undefined weak symbols to zero. Otherwise, we will get
>>>>> run-time
>>>>> relocation overflow for dynamic R_X86_64_32/R_X86_64_PC32 relocations.
>>>>>
>>>> This is what I am checking in.
>>>>
>>>>
>>> I'm seeing:
>>>
>>> NA->FAIL: Mixing PIC and non-PIC
>>> on aarch64-none-linux-gnu.
>>
>> You can either fix aarch64 backend or skip the test for aarch64.
>
>
> H.J,
>
> For your testcase, AArch64 is not generating dynamic relocation for
> weak undefined symbol referenced from non-pic code when linking
> exectuable, instead, it's resolved to zero during static linking stage.
> As far as I know, this behavior is exactly what's described here at
>
> https://sourceware.org/ml/binutils/2008-04/msg00269.html
>
> And reading those historical discussions,
>
> https://sourceware.org/ml/binutils/2008-04/msg00032.html
> https://sourceware.org/ml/binutils/2008-02/msg00264.html
>
> Looks to me the ld behavior changes introduced by your patch is quite
> sensitive and there still be lack of consensus.
What linker change were you referring to? I only added a testcase.
> Therefore, instead of skipping this testcase on AArch64 (I guess a few
> other targets will fail on native tests as well), can you please only
> enable this testcase on x86 arches firstly?
These backends are also broken.
--
H.J.