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Re: [PATCH] Enable hidden visibility in libc.a compiled with PIE
- From: "H.J. Lu" <hjl dot tools at gmail dot com>
- To: Szabolcs Nagy <szabolcs dot nagy at arm dot com>
- Cc: GNU C Library <libc-alpha at sourceware dot org>, nd <nd at arm dot com>
- Date: Mon, 21 Aug 2017 09:44:31 -0700
- Subject: Re: [PATCH] Enable hidden visibility in libc.a compiled with PIE
- Authentication-results: sourceware.org; auth=none
- References: <20170808164040.GA31184@gmail.com> <599B0AEC.5080308@arm.com>
On Mon, Aug 21, 2017 at 9:31 AM, Szabolcs Nagy <szabolcs.nagy@arm.com> wrote:
> On 08/08/17 17:40, H.J. Lu wrote:
>> When building libc.a with PIE, enable hidden visibility to allow direct
>> access to definitions within libc.a without using GOT.
> ...
>> -#if defined SHARED || defined LIBC_NONSHARED
>> +#if defined SHARED || defined LIBC_NONSHARED \
>> + || (BUILD_PIE_DEFAULT && IS_IN (libc))
>> # define attribute_hidden __attribute__ ((visibility ("hidden")))
>
> btw what happens if this is enabled for non-pie libc.a ?
It makes those symbols in libc.a hidden.
> i'd expect that to work too (it prevents some symbol
> interpositions?)
>
You can't interpose any symbols in libc.a, PIE or non-PIE.
What my patch does is to avoid GOT/PLT in PIE libc.a when
accessing them within libc.a.
--
H.J.