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Re: Copy relocations against protected symbols
- From: "H.J. Lu" <hjl dot tools at gmail dot com>
- To: Cary Coutant <ccoutant at google dot com>, Binutils <binutils at sourceware dot org>, GNU C Library <libc-alpha at sourceware dot org>
- Date: Thu, 18 Dec 2014 15:06:14 -0800
- Subject: Re: Copy relocations against protected symbols
- Authentication-results: sourceware.org; auth=none
- References: <CAMe9rOoJ-0ER8VAckjZyLwdgGJFeQBfri+d+NY81WozizTnCQw at mail dot gmail dot com> <20141218221354 dot GA31055 at bubble dot grove dot modra dot org>
On Thu, Dec 18, 2014 at 2:13 PM, Alan Modra <amodra@gmail.com> wrote:
> On Thu, Dec 18, 2014 at 11:02:59AM -0800, H.J. Lu wrote:
>> Adding glibc.
>>
>> On Thu, Dec 18, 2014 at 10:52 AM, Cary Coutant <ccoutant@google.com> wrote:
>> >> Should we simply disallow creating DSO with protected data on targets
>> >> with copy relocation?
>> >
>> > I don't think so. Protected symbols are useful, and their presence
>>
>> As soon as they are used in executable, the program will misbehave.
>
> Not if the references in the executable are in code compiled with
> -fPIC. I agree with Cary, disallowing protected visibility variables
It only works with -fPIC, not -fPIE when GCC 5 is used:
https://gcc.gnu.org/ml/gcc-patches/2014-12/msg00428.html
Are we suggesting we should compile PIE with -fPIC now?
> in shared libraries, or disabling the compiler optimisation that
> allows shared library code to access protected variables without a GOT
> indirection, is too big a hammer.
--
H.J.