News Group Posts

gcc sco 5.0.7, Undefined symbol

_fini5

From: Jean-Pierre Radley <jpr@jpr.com>
Subject: Re: gcc on 5.0.7
Date: 15 Jul 2003 10:28:00 -0400

Jean-Pierre Radley wrote:
> Kean, this is from the newsgroup.  Sum it up for Roger, would you please?
> 
> Roger Cornelius typed (on Mon, Jul 14, 2003 at 02:38:15PM -0700):
> | Ever since installing Openserver 5.0.7, I am unable to use gcc 3.2.1. 
> | It returns an Undefined symbol _fini error for any compilation
> | attempt.
> | 
> | I tried installing the Gnu Development Tools from the OS installation
> | CD and that gcc works so far as I've tested, but it's unable to
> | build/bootstrap gcc 3.3 and fails at some point with the _fini error.
> | 
> | Using the SCO provided cc to build gcc, make fails with an "undefined
> | symbol: DEFAULT_PCC_STRUCT_RETURN" error in i386.c for 3.2.2, and
> | configure fails with an "cannot determine size for long long" error
> | for gcc 3.3.
> | 
> | I've watched the c.u.s.* and gcc newsgroups and checked the gcc web
> | site but have not found any answers or significant discussion.  Am I
> | missing something?

Jean-Pierre,

Can you mirror this reply to the newgroup so that others that watch it 
can learn about this too?

Roger, heres the scoop. When you create an executable with a compiler, 
you not only link in your objects and libraries, but behind the scenes, 
the compiler driver (gcc, cc, whatevercc) will prepend special system 
object files, and append other special ones. For C programs, these are 
known as the CRT (C run-time) files. These typically do things like set 
up the float point environment, set up any profiling counters and calls, 
call any global initialization code and then finally call main(). When 
the program terminates via any mechanism that uses exit(), then some 
special code that is appended by the CRT files does global destruction 
and other cleanups, calculates profiling totals, and then actually exits.

In ELF objects, code and data are put into special named "sections". 
These are controlled by the ".section" assembler directive, and its 
abbreviations like ".text" which is basically ".section .text" and 
".data" which is essentially ".section .data". Code goes into the 
section called .text, and data goes into the sections .data, .rodata or 
.bss, depending on how the data is declared. There are several sections 
which are very special to ELF. For your actual problem as experienced, 
these are the .init section and the .fini section. These are designed to 
have initialization and finalization code, respectively. When you link 
edit an ELF program, the ELF ABI states that all code in a .init section 
is executed before main() and that call code in a .fini section is 
executed before exiting. This is how C++ global constructors and 
destructors are implemented.

Although you are not experiencing problems with this yet, I want to 
document this for the sake of completion, since this message will 
hopefully make its way to the newsgroup and other people may or may not 
be experiencing other problems.

Modern ELF extended the notion of the .init and .fini sections with 
three special sections: .preinit_array, .init_array and .fini_array. 
These arrays store pointers to functions, not arbitrary code as .init 
and .fini do. The gABI specifies that each entry in the .preinit_array 
section is executed before the program entry point. This means it gets 
executed before the CRT stuff gets invoked, which means it gets executed 
before any code in the .init section. Likewise, the functions in 
.init_array are also called before the entry point. Shared libraries 
have .init_array called every time they are loaded. The system also sets 
things up such that functions in .fini_array are called when a shared 
library is unloaded and before functions in the .fini section when the 
program exits normally.

So thats what the code needs to do. Here is why you were having a 
problem. Typically, the CRT is divided into three files. crt1.o, crti.o 
and crtn.o. crt1.o contains the actual C startup stuff, and work some 
magic to interact with teh run-time link editor (RTLD). crti.o contails 
a single function, called _init, that is inserted at the very beginning 
of the .init section. The same applies to a function called _fini and 
starts the .fini section. These function do nothing, they are empty. 
crtn.o, which is one of the last objects link edited into the program 
or shared library, terminates the .init and .fini sections with a simple 
return instruction. Thus, when you link edit a program, you get the 
deifintion of the _init function, then the code from all of your program 
objects, in order, with their .init and .fini sections, then the 
termination from crtn.o. This results in a single contiguous function 
such that when _init is called, all code from all .init sections is 
executed linearly in object order, and all code from all .fini sections 
is executed in object order.

When you link edit a program, you use all three startup files: crt1.o, 
crti.o yourobjects.o libraries.so crtn.o. When you link edit a shared 
library, you typically omit crt1.o, as the code in it has no meaning to 
a shared library. There is no need to set up calls to main or reset the 
floating point environment or set up profiling counters. In fact, doing 
so can completely screw your program up. Consider, for example, if you 
had carefully set up your floating point environment to be in IEEE mode, 
and the code in crt1.o sets it to some other mode. Or consider the fact 
that profiling counters may get reset erroneously. All the shared 
libraries need is the stuff in crti.o and crtn.o, to start and finish 
the .init and .fini sections (and correspondingly the _init and _fini 
functions for that shared libary).

In releases prior to 5.0.7, OpenServer did not have a crti.o. It had the 
_init stub in crt1.o. This caused untold grief, especially when we 
started using G++ to create shared libraries. So, starting in release 
5.0.7, I split out the stub stuff from crt1.o and put it in crti.o where 
it always should have been. The native compiler driver (cc) was changed 
to link with crti.o and so was the officially supported version of GCC 
(2.95.3). At the time that I made this change, there was no mor work 
being done on the 2.95 branch of GCC, they were in the middle of doing 
GCC 3.2. We didnt fully trust the GCC 3 branch yet which is why we never 
did any work on it to update it to use crti.

However, things are now to the point where we will be adopting GCC 3 as 
the officially supported version of GCC. This will happen for release 
5.0.8 of SCO OpenServer. To that end, I did all the required work to get 
this stuff working in GCC 3. At the time that I did the work, they were 
at the tail end of getting ready to release 3.3, and the GCC Steering 
Committee decided that these changes were not appropriate for that 
release. Thus, these changes were put in at the head of the tree, and 
are in (or will be in, when it is releaed) GCC 3.4. If you really want a 
GCC 3.x release, you need to check out the head of the tree to get this 
stuff. I was intending to backport the changes to 3.3.1 but I have not 
had the time. If there is ever a 3.3.2, it may go into that but I 
suspect that the steering committee will veto that notion. For for GCC 
3.x, the first version that will be known to work propperly on OSR5 is 3.4.

If you are feeling brave, when 3.3.1 is released in a few days/weeks, 
you can get the stuff from the head from CVS, look at the changelogs for 
what I had to do for OSR5 and back-port it. I may do that myself if I 
have the time, and then get Boyd Lynn-Gerber to post the required patch 
on his website where he collects such things. In two short weeks we will 
be releasing a significan update to the GNU Development Tools package, 
which provides the current officially supported GCC and a plethora of 
other GNU tools that software developers frequently use. This will rely 
on Support Level Supplement OSS646B, which is the execution environment 
update. This update fixes the RTLD, libc and crt*.o files such that they 
meet the gABI requirements, as outlined above. As far as I am concerned 
every OpenServer system from 5.0.4 on upwards should install OSS646B, 
but some administrators are loathsome to install such big changes and 
thats a whole other issue.

Hope this helps.

Kean

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