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Re: [RFC] Hide autogenerated symbols when linking shared libraries
- From: Nick Clifton <nickc at redhat dot com>
- To: Yuri Gribov <tetra2005 at gmail dot com>, binutils at sourceware dot org
- Date: Tue, 1 May 2018 17:00:52 +0100
- Subject: Re: [RFC] Hide autogenerated symbols when linking shared libraries
- Autocrypt: addr=nickc at redhat dot com; prefer-encrypt=mutual; keydata= xsFNBFm/2cUBEADkvRqMWfAryJ52T4J/640Av5cam9ojdFih9MjcX7QWFxIzJfTFYq2z+nb4 omdfZosdCJL2zGcn6C0AxpHNvxR9HMDkEyFHKrjDh4xWU+pH4z9azQEqJh331X7UzbZldqQo 16VkuVavgsTJaHcXm+nGIBTcUbl2oiTtHhmuaYxx6JTMcFjC7vyO5mLBw78wt52HBYweJ0Nj HBvvH/JxbAAULSPRUC61K0exlO49VFbFETQNG1hZTKEji95fPbre7PpXQ0ewQShUgttEE/J3 UA4jYaF9lOcZgUzbA27xTV//KomP0D30yr4e4EJEJYYNKa3hofTEHDXeeNgM25tprhBUMdbV RZpf2Keuk2uDVwc+EiOVri48rb1NU+60sOXvoGO6Ks81+mhAGmrBrlgLhAp8K1HPHI4MG4gH nrMqX2rEGUGRPFjC3qqVVlPm8H05PnosNqDLQ1Pf7C0pVgsCx6hKQB7Y1qBui7aoj9zeFaQg pYef+CEERIKEcWwrjaOJwK3pi9HFdxS0NNWYZj8HPzz/AsgTTQdsbulPlVq2SsctmOnL42CZ OCTppGYwl53CG/EqVY+UQBzFzJBaY8TJRFFYVEy5/HH4H11rMoZwqIkk71EOGU3X6mWlANRi kR3M4GhVITRzuaV69Fed+OeXcCmP94ASLfuhBR2uynmcHpBKpwARAQABzTtOaWNrIENsaWZ0 b24gKENoaWVmIEJpbnV0aWxzIE1haW50YWluZXIpIDxuaWNrY0ByZWRoYXQuY29tPsLBeAQT AQIAIgUCWb/ZxQIbAwYLCQgHAwIGFQgCCQoLBBYCAwECHgECF4AACgkQE/zvid2ePE9cOxAA 3cX1bdDaTFttTqukdPXLCtD2aNwJos4vB4LYPSgugLkYaHIQH9d1NQPhS0TlUeovnFNESLaV soihv0YmBUCyL4jE52FRoTjE6fUhYkFNqIWN2HYwkVrSap2UUJFquRVoVbPkbSup8P+D8eyd BbdxsY6f+5E8Rtz5ibVnPZTib7CyqnFokJITWjzGdIP0Gn+JWVa6jtHTImWx1MtqiuVRDapU hrIoUIjf98HQn9/N5ylEFYQTw7tzaJNWeGUoGYS8+8n/0sNbuYQUU/zwMVY9wpJcrXaas6yZ XGpF/tua59t9LFCct+07YAUSWyaBXqBW3PKQz7QP+oE8yje91XrhOQam04eJhPIBLO88g6/U rdKaY7evBB8bJ76Zpn1yqsYOXwAxifD0gDcRTQcB2s5MYXYmizn2GoUm1MnCJeAfQCi/YMob R+c8xEEkRU83Tnnw3pmAbRU6OcPihEFuK/+SOMKIuV1QWmjkbAr4g9XeXvaN+TRJ9Hl/k1k/ sj+uOfyGIaFzM/fpaLmFk8vHeej4i2/C6cL4mnahwYBDHAfHO65ZUIBAssdA6AeJ+PGsYeYh qs6zkpaA2b0wT4f9s7BPSqi0Veky8bUYYY7WpjzDcHnj1gEeIU55EhOQ42dnEfv7WrIAXanO P8SjhgqAUkb3R88azZCpEMTHiCE4bFxzOmjOwU0EWb/ZxQEQALaJE/3u23rTvPLkitaTJFqK kwPVylzkwmKdvd2qeEFk1qys2J3tACTMyYVnYTSXy5EJH2zJyhUfLnhLp8jJZF4oU5QehOaJ PcMmzI/CZS1AmH+jnm6pukdZAowTzJyt4IKSapr+7mxcxX1YQ2XewMnFYpLkAA2dHaChLSU/ EHJXe3+O4DgEURTFMa3SRN/J4GNMBacKXnMSSYylI5DcIOZ/v0IGa5MAXHrP1Hwm1rBmloIc gmzexczBf+IcWgCLThyFPffv+2pfLK1XaS82OzBC7fS01pB/eDOkjQuKy16sKZX6Rt57vud4 0uE5a0lpyItC2P7u7QWL4yT5pMF+oS8bm3YWgEntV380RyZpqgJGZTZLNq2T4ZgfiaueEV4J zOnG2/QRGjOUrNQaYzKy5V127CTnRg4BYF/uLEmizLcI3O3U1+mEz6h48wkAojO1B6AZ8Lm+ JuxOW5ouGcrkTEuIG56GcDwMWS/Pw/vNsDyNmOCjy9eEKWJgmMmLaq59HpfTd8IOeaYyuAQH AsYt/zzKy0giMgjhCQtuc99E4nQE9KZ44DKsnqRabK9s3zYE3PIkCFIEZcUiJXSXWWOIdJ43 j+YyFHU5hqXfECM6rzKGBeBUGTzyWcOX6YwRM4LzQDVJwYG8cVfth+v4/ImcXR43D4WVxxBE AjKag02b+1yfABEBAAHCwV8EGAECAAkFAlm/2cUCGwwACgkQE/zvid2ePE/dqQ/6ApUwgsZz tps0MOdRddjPwz44pWXS5MG45irMQXELGQyxkrafc8lwHeABYstoK8dpopTcJGE3dZGL3JNz 1YWxQ5AV4uyqBn5N8RubcA8NzR6DQP+OGPIwzMketvVC/cbbKDZqf0uTDy3jP65OFhSkTEIy nYv1Mb4JJl3Sq+haUbfWLAV5nboSuHmiZE6Bz2+TjdoVkNwHBfpqxu6MlWka+P98SUcmY8iV hPy9QC1XFOGdFDFf1kYgHW27mFwds35NQhNARgftAVz9FZXruW6tFIIfisjr3rVjD9R8VgL7 l5vMr9ylOFpepnI6+wd2X1566HW7F1Zw1DIrY2NHL7kL5635bHrJY4n7o/n7Elk/Ca/MAqzd IZxz6orfXeImsqZ6ODn4Y47PToS3Tr3bMNN9N6tmOPQZkJGHDBExbhAi/Jp8fpWxMmpVCUl6 c85cOBCR4s8tZsvGYOjR3CvqKrX4bb8GElrhOvAJa6DdmZXc7AyoVMaTvhpq3gJYKmC64oqt 7zwIHwaCxTbP6C6oUp9ENRV7nHnXN3BlvIgCo4QEs6HkDzkmgYlCEOKBiDyVMSkPDZdsspa+ K4GlU2Swi/BDJMjtDxyo+K0M81LXXxOeRfEIfPtZ3ddxBKPva1uSsuz+pbN9d1JY8Ko5T/h1 6susi2ReUyNJEJaSnjO5z13TQ1U=
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- References: <CAJOtW+4ifhHp4R3z6pfD2bSaSOjh8hb3LafxFDdR8pbc3RysOg@mail.gmail.com>
Hi Yuri,
> Currently default linker script
For which target(s) ?
> generates several temporary symbols
> which globally visible and unnecessarily increase size of dynamic
> symtable:
> $ gcc -shared -fPIC -O2 tmp.c -o tmp.so
> $ readelf --dyn-syms -W tmp.so
> ...
> 7: 0000000000201020 0 NOTYPE GLOBAL DEFAULT 21 _edata
> 9: 0000000000201028 0 NOTYPE GLOBAL DEFAULT 22 _end
> 10: 0000000000201020 0 NOTYPE GLOBAL DEFAULT 22 __bss_start
>
> Is this intentional?
Yes. Sometime these symbols are used by the crt initialization code.
For example, on bare metal systems the sbrk() function often uses the
_end symbol as the starting address for the heap.
Also tools like the dynamic loader, profilers, gdb and so on, sometimes
make use of these symbols too. So unless you are really short on space
I would recommend leaving them in.
Cheers
Nick
PS. You can always create your own linker script which does not define
these symbols...