_dl_open in libc.so?

KillerCode · 03-11-2011, 11:15 AM

i know that there is a function in libld.so called dlopen for share libraries loading, but i heard that there is another function called _dl_open in libc.so (which is better than libld.so sine libc is more reliable and guaranteed to exists) also if i used libc.so will be better to reduce libraries used by my software.
but i cant seem to find it in any include files :/

cheers;
thanks.

knudfl · 03-11-2011, 12:04 PM

/usr/lib/libc.so is a text file :

Code:

/* GNU ld script
   Use the shared library, but some functions are only in
   the static library, so try that secondarily.  */
OUTPUT_FORMAT(elf32-i386)
GROUP ( /lib/libc.so.6 /usr/lib/libc_nonshared.a  AS_NEEDED ( /lib/ld-linux.so.2 ) )

/lib/ld-linux.so.2 -> ld-2.10.1.so ( Provided by glibc ).

Code:

 $ readelf -s /lib/ld-linux.so.2 | grep dl_open
   196: 4806c750  2145 FUNC    LOCAL  DEFAULT   10 dl_open_worker
   373: 4806c250   616 FUNC    LOCAL  HIDDEN   10 _dl_open

KillerCode · 03-11-2011, 12:53 PM

i dont get it !

knudfl · 03-11-2011, 02:23 PM

You were looking for the object by name "_dl_open".

"_dl_open" is in the library ld-<glibc-version>.so .

'ld-linux.so.2' is a link to 'ld-<glibc-version>.so'

And that library is created when glibc is being build.

Please explain, what it is, you don't understand.

..

Sergei Steshenko · 03-11-2011, 02:37 PM

Quote:

Originally Posted by KillerCode

i dont get it !

A library may be an object file or a linker script.

KillerCode · 03-12-2011, 10:23 PM

ok, thats new, so no _dl_open in libc? i thought because libc is already used by my app, so i can use all functions from it, and avoid linking libld.so.

so this means there is no way out? ill have to link to libld.so?

knudfl · 03-14-2011, 02:20 AM

Quote:

so no _dl_open in libc ?

The object ""_dl_open"" is in libc only ! Nowhere else ! → → post # 2

The name of the libc library holding this object is ld-<glibc-version>.so

KillerCode · 03-14-2011, 08:54 AM

oh, so i still have to link another library? if thats the case then its pointless !!

knudfl · 03-14-2011, 11:53 AM

ld-<glibc-version>.so is always installed.

All binaries, including all commands depend on ld-linux.so.2 -> ld-<glibc-version>.so

..

wilkux · 03-30-2011, 06:09 PM

How can I load a library using this function and nasm, when I know the function address? I know that in eax I should store pointer to the string with new library path, in ebx mode (probably 0x80000000 | RTLD_LAZY, but why 0x80000000?), and what about ecx? What should be placed there? I found that the caller, but what it's?

knudfl · 03-31-2011, 04:59 AM

Post #10 , @ wilkux : Welcome to LQ.

Looks like an off topic question. Please read :
http://www.linuxquestions.org/linux/...Ask_a_Question
http://linuxsilo.net/docs/smart-questions_en.html
http://www.linuxquestions.org/linux/rules.html

And start a new thread with your question ..
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