Issue while using -rdynamic with binutils 2.22-8

[Makarand Pradhan]

On 30/01/14 10:43 AM, H.J. Lu wrote:
> On Thu, Jan 30, 2014 at 7:09 AM, Makarand Pradhan
> <makarandpradhan@ruggedcom.com>  wrote:
>> On 29/01/14 06:26 PM, H.J. Lu wrote:
>>> On Wed, Jan 29, 2014 at 2:12 PM, H.J. Lu<hjl.tools@gmail.com>   wrote:
>>>> On Wed, Jan 29, 2014 at 1:31 PM, Makarand Pradhan
>>>> <makarandpradhan@ruggedcom.com>   wrote:
>>>>> Hi All,
>>>>>
>>>>> We are in the process of migrating from binutils 2.20.1-16 to 2.22-8.
>>>>>
>>>>> I notice an issue while using linker option -rdynamic. Details below:
>>>>>
>>>>> I'm using the sample code given at the end of this email for the test.
>>>>> The
>>>>> code links fine in 2.20.1-16, but fails in 2.22-8.
>>>>>
>>>>> e.g.:
>>>>> In 2.20.1-16:
>>>>> # g++ -ffunction-sections -fdata-sections -rdynamic -Wl,--gc-sections
>>>>> t.cpp
>>>>> #
>>>>>
>>>>> In 2.22-8:
>>>>> # g++ -ffunction-sections -fdata-sections -rdynamic -Wl,--gc-sections
>>>>> t.cpp
>>>>> /tmp/ccU6re3d.o: In function `c1_type::c1_func1()':
>>>>> t.cpp:(.text._ZN7c1_type8c1_func1Ev+0x12): undefined reference to
>>>>> `c1_type::int_1'
>>>>> t.cpp:(.text._ZN7c1_type8c1_func1Ev+0x1e): undefined reference to
>>>>> `c1_type::int_1'
>>>>> collect2: ld returned 1 exit status
>>>>>
>>>>> Problem:
>>>>> The unused code is supposed to be stripped of by -Wl,--gc-sections. When
>>>>> used alone it works as expected. All the same when paied with �rdynamic
>>>>> the
>>>>> build fails in the newer version.
>>>>>
>>>>> Would appreciate any opinions if this is a bug or if I'm missing
>>>>> anything.
>>>>>
>>>>> Warm Rgds,
>>>>> Makarand.
>>>>>
>>>>> System configuration:
>>>>> # uname -a
>>>>> Linux makarandpradhan-ppc 3.2.0-0.bpo.4-powerpc64 #1 SMP Debian
>>>>> 3.2.41-2+deb7u2~bpo60+1 ppc GNU/Linux # cat /etc/*release
>>>>> PRETTY_NAME="Debian GNU/Linux 7 (wheezy)"
>>>>> NAME="Debian GNU/Linux"
>>>>> VERSION_ID="7"
>>>>> VERSION="7 (wheezy)"
>>>>> ID=debian
>>>>> ANSI_COLOR="1;31"
>>>>> HOME_URL="http://www.debian.org/"
>>>>> SUPPORT_URL="http://www.debian.org/support/"
>>>>> BUG_REPORT_URL="http://bugs.debian.org/"
>>>>>
>>>>>
>>>>> File: t.cpp
>>>>> #include<stdio.h>
>>>>>
>>>>> class c1_type
>>>>> {
>>>>> public:
>>>>> static int int_1;
>>>>>
>>>>> void c1_func1(void);
>>>>> };
>>>>>
>>>>> void c1_type::c1_func1()
>>>>> {
>>>>> int_1 = 25;
>>>>> }
>>>>>
>>>>> int main()
>>>>> {
>>>>> return 0;
>>>>> }
>>>>>
>>>> This regression is caused by
>>>>
>>>> https://sourceware.org/ml/binutils/2011-11/msg00056.html
>>>>
>>> I think your code is invalid.  You need either to provide definition
>>> for
>>>
>>> static int int_1;
>>>
>>> or drop -rdynamic.
>>
>> Hi H.J. Lu,
>>
>> Appreciate your replies.
>>
>> The definition is intentionally dropped so that it is stripped by
>> -Wl,--gc-sections. Only when used in conjunction with -rdynamic it causes a
>> problem.
>>
>> I could successfully use both -Wl,--gc-sections and -rdynamic in 2.20.1-16
>> but it fails in 2.22-8.
>>
>> That's why I was wondering if any commit has caused this change. And if this
>> is intentional or a bug.
>>
>>
> -rdynamic tells linker to make ALL global symbols available for
> dynamic linking, including those unused.  You have
>
> void c1_type::c1_func1()
> {
> int_1 = 25;
> }
>
> Linker will export it even if --gc-sections is used.  When -rdynamic
> is used, --gc-sections will only discard unused LOCAL symbols.
> This is the bug fixed in binutils 2.21.
>
Thanks.

-- 
Makarand Pradhan
Software Engineer Ruggedcom
Siemens Canada Limited
Industry Sector
300 Applewood Crescent,
Vaughan, ON, L4K 5C7
Tel: 905 482 4572
e-mail:  makarand.pradhan@siemens.com
www.ruggedcom.com