ELF executable + library calls?

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AMD64

Joined: 19 Sep 2003
Posts: 8

AMD64 08 May 2008, 10:30

When an executable ELF module is assembled, the extrn directive isn't functional, this is also stated in the docs. But, shouldn't there be a way to call external library functions from all those ".so" libraries...? Sure I could create a non-executable ELF-object with FAsm, use extrn, and link the module with gcc (ld),.. but would be nice to be able to code it all with one tool. Just like windows PE-exes can be very nicely crafted with just using FAsm.

Not sure if I'm missing something, but shouldn't the Linux library-import system work just like the thing with non-executable linkable objects..? But just using dynamic linking... or would I need to call some kernel functions myself through int 80h to load the library and do some dark magic trickery to find the function addresses... I don't think (or at least hope) so... Wink

Sorry, this is prolly a very silly question, but I'm a n00b in Linux asm coding. Some experinced guy come and help me out, please... Wink

08 May 2008, 10:30

Chewy509

Joined: 19 Jun 2003
Posts: 297
Location: Bris-vegas, Australia

Chewy509 09 May 2008, 03:26

The dlopen(), dlysm() and dlclose() functions are the ones you're after if you are building an Executable ELF directly and wish to load *.so's at runtime (eg if you're using a plug-in architecture when you don't know in advance what *.so's you're linking to)...

http://www.opengroup.org/onlinepubs/009695399/functions/dlopen.html

Or otherwise build you're asm file as an Object ELF file (and hence the extern is available), and link to the *.so's using either gcc or ld to create your executable.

eg

Code:

> fasm myfile.asm myfile.o
> gcc -lGL -lDSL -lm -o myfile myfile.o
> ldd -r main
   libc.so.1 =>     /usr/lib/libc.so.1
   libelf.so.1 =>   /usr/lib/libelf.so.1
   libm.so =>       /usr/lib/libm.so
   libGL.so =>      /usr/X11R6/lib/libGL.so
   libSDL.so =>     /usr/lib/libSDL.so

(The -lGL denotes to link to libGL.so)...

09 May 2008, 03:26

Endre

Joined: 29 Dec 2003
Posts: 215
Location: Budapest, Hungary

Endre 09 May 2008, 07:34

links below may help you:

http://board.flatassembler.net/topic.php?t=7490
http://board.flatassembler.net/topic.php?t=8653

09 May 2008, 07:34

AMD64

Joined: 19 Sep 2003
Posts: 8

AMD64 10 May 2008, 15:30

Thank you for your help fellows.
I get it now. Wink

Just lately abandoned Windows and switched to Linux completely... time has come for it. Not going back. Ever Wink

Internal support for extrn + executable elf in fasm would be nice, but no problem... just wanted to hyper-optimize a little proggy Wink

Well, dunno how much fluff does using ld bring in the program... shouldn't be much, as it should just create the import stuff needed and nothing else, if calling gcc with -nostdlib switch.

Thanks again... and may the future be filled with penguins... Wink

10 May 2008, 15:30

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