|
|
|
|
|
|
| Author |
Message |
Henrik Goldman
*nix forums Guru Wannabe
Joined: 26 Mar 2006
Posts: 102
|
 Posted: Thu Jun 08, 2006 9:26 am Post subject:
Hiding symbols in shared library
|
|
|
I would like to link a shared library and only make the symbols to be
exported as global.
By this I mean that I want to override the default settings and mark most of
the symbols local.
Thus I do the following:
g++ -mlp64 temp/file.o -o
temp/libfoobar.so -static-libgcc -shared -Wl,+hideallsymbols -Wl,-e -Wl,A -Wl,-e
-Wl,B
However I end up in ALOT of warnings by the linker for all the undefined
symbols.
Is there any other way to acomplish this? Lots of other linkers (sun, linux,
aix etc.) accept a script file which allows one to write the nessecary
symbols into but it doens't seem like hp ld provides this option.
Thanks in advance.
-- Henrik |
|
| Back to top |
|
 |
Carl Burch
*nix forums beginner
Joined: 08 Apr 2005
Posts: 17
|
| Posted: Thu Jun 08, 2006 4:13 pm Post subject:
Re: Hiding symbols in shared library
|
|
|
| Quote: | Is there any other way to acomplish this? Lots of other linkers (sun, linux,
aix etc.) accept a script file which allows one to write the nessecary
symbols into but it doens't seem like hp ld provides this option.
|
Sure, the -c option does that :
-c filename Read ld options from a file. Each line
contains
zero or more arguments separated by white
space.
Each line in the file, including the last
line,
must end with a newline character. A #
character
implies that the rest of the line is a
comment.
To escape a # character, use the sequence ##.
Note that the file is a list of options, not symbols to be hidden. You
need to put -h
ahead of every symbol name you want to hide.
- Carl Burch
HP WDB Team |
|
| Back to top |
|
|
Henrik Goldman
*nix forums Guru Wannabe
Joined: 26 Mar 2006
Posts: 102
|
| Posted: Thu Jun 08, 2006 8:38 pm Post subject:
Re: Hiding symbols in shared library
|
|
|
| Quote: | Sure, the -c option does that :
Note that the file is a list of options, not symbols to be hidden. You
need to put -h
ahead of every symbol name you want to hide.
|
So you're saying I should combine this with 'nm' utility to filter out all
the symbols I want to hide and then make them into a list which is written
into a file?
I must say that I understand what needs to be done but it's not trivial.
Perhaps it's just the lack of my scripting skills. All this because ld
doesn't support similar features as ld on almost all other platforms.
An example would be nice.
-- Henrik |
|
| Back to top |
|
|
Carl Burch
*nix forums beginner
Joined: 08 Apr 2005
Posts: 17
|
| Posted: Fri Jun 09, 2006 4:18 pm Post subject:
Re: Hiding symbols in shared library
|
|
|
Henrik-
| Quote: | So you're saying I should combine this with 'nm' utility to filter out all
the symbols I want to hide and then make them into a list which is written
into a file?
|
That's what I thought you were asking for. My apologies for not
understanding your question on the first try.
| Quote: | I must say that I understand what needs to be done but it's not trivial.
Perhaps it's just the lack of my scripting skills. All this because ld
doesn't support similar features as ld on almost all other platforms.
An example would be nice.
|
I agree. Can you say exactly which linker option on which
operating system gives the feature you want? Quoting the man page for
that option would help, as I may not have access to the type of system
you cite.
- Carl Burch
HP WDB Team |
|
| Back to top |
|
|
Henrik Goldman
*nix forums Guru Wannabe
Joined: 26 Mar 2006
Posts: 102
|
| Posted: Fri Jun 09, 2006 9:02 pm Post subject:
Re: Hiding symbols in shared library
|
|
|
| Quote: | I agree. Can you say exactly which linker option on which
operating system gives the feature you want? Quoting the man page for
that option would help, as I may not have access to the type of system
you cite.
|
For instance on linux we have linker scripts:
http://unixhelp.ed.ac.uk/CGI/man-cgi?ld
Notice the switch --version-script. This is a good one because I can create
simple scripts like:
mylib
{
global:
symbolA;
symbolB;
symbolC;
local:
*;
};
Notice how much easier this is then the hp linker. I only would have to
specify what I want to be exported instead of saying everything that I don't
want to have exported. Naturally this list is much smaller.
The next problem is that I need to find which symbols to hide. Some
additional processing to 'nm' output is therefore needed and it is a little
bit tricky to ensure that I don't miss any symbols.
More advice is really welcome on this issue. I wouldn't have imagined that
it would be so tricky to do something really simple.
After all I cannot be the first man in the world who wanted to create a
shared library with known exports, right?
Thanks in advance.
-- Henrik |
|
| Back to top |
|
|
Carl Burch
*nix forums beginner
Joined: 08 Apr 2005
Posts: 17
|
| Posted: Fri Jun 09, 2006 10:15 pm Post subject:
Re: Hiding symbols in shared library
|
|
|
Henrik Goldman wrote:
| Quote: | I agree. Can you say exactly which linker option on which
operating system gives the feature you want? Quoting the man page for
that option would help, as I may not have access to the type of system
you cite.
For instance on linux we have linker scripts:
http://unixhelp.ed.ac.uk/CGI/man-cgi?ld
Notice the switch --version-script. This is a good one because I can create
simple scripts like:
mylib
{
global:
symbolA;
symbolB;
symbolC;
local:
*;
};
|
Thanks for the URL, that makes it clear that what you're talking
about is the aside in the Linux ld(1) man page :
You can also use the version script to control what symbols
should
be added to the dynamic symbol table if the output format supports
it. See the description of --version-script in @ref{VERSION}.
So what you're concerned about is whether the symbols are added to the
default
export list or subtracted from them. In my original answer I
inadvertantly gave
you the subtractive answer, while you wanted the additive option. On
HP-UX that's :
+e symbol When building a shared library or program,
mark
the symbol for export to the dynamic loader.
Only
symbols explicitly marked are exported. When
building a shared library, calls to symbols
that
are not exported are resolved internally.
If you use the +e or +ee option with -B
symbolic,
references to the symbol specified are
resolved
internally if defined. The runtime behavior
may
be different from using +e alone.
You can specify more than one symbol on the
command line with multiple option-symbol
pairs,
that is, each symbol you specify must be
preceded
by the +e option.
There's also the +ee option, with slightly different semantics with
regard to whether it changes the default export behavior. It sounds
more like the Linux feature you cite, since it leaves the default
exported symbol list in place, while +e empties the list before adding
the symbol(s) you want. Which behavior is better depends on whether
you want tight control or still want to default some symbols' behavior.
Once you start playing with symbol visibility you're likely to have
to figure out symbols that are added by the implementation, so +e is
probably a better choice. I highly recommend the "HP-UX Linker and
Library User's Guide" at http://docs.hp.com/en/B2355-90655/index.html.
- Carl Burch
HP WDB Team |
|
| Back to top |
|
|
Eric Gouriou
*nix forums beginner
Joined: 08 Sep 2005
Posts: 8
|
| Posted: Fri Jun 09, 2006 10:36 pm Post subject:
Re: Hiding symbols in shared library
|
|
|
Henrik Goldman wrote:
| Quote: | After all I cannot be the first man in the world who wanted to create a
shared library with known exports, right?
|
Use the __declspec directives in the source to explicitely mark your
exports, then use the command line options to hide the rest.
It is supported by not-too-old aCC (PA and IPF it seems), gcc and
is standard in the Microsoft world.
From a quick google "site:docs.hp.com __declspec":
----------------------------------
o Support for _declspec
This release supports __declspec(dllimport) and
__declspec(dllexport) as keywords. These keywords have the same
semantics as in Microsoft Windows compilers and ease porting of
applications developed in Microsoft Windows compilers to HP-UX
systems.
Support of these keywords enhances the performance of shared libraries
and relieves the usage of HP_DEFINED_EXTERNAL pragmas and
+Oextern= list to hide the non-exported symbols.
Syntax & Semantics:
__declspec ( extended-attribute ) declarator
extended-attribute:
dllimport
| dllexport
1. Declaring a symbol with external linkage as __declspec(dllexport)
tells the compiler that the symbol should be exported from the
current load module (shared library) and made visible to other
load modules.
2. Declaring a symbol with external linkage as __declspec(dllimport)
tells the compiler that the symbol is defined in a shared
library and is outside the current load module.
3. Declaring a class with either the __declspec(dllexport) or
__declspec(dllimport) keyword results in all its member functions
and static data members being marked for export or import.
4. Only symbols having external linkage can be declared using these
keywords.
5. It is legal to selectively specify members of a class as dllexport
or dllimport but selective specification is not allowed if the
class itself is exported or imported.
----------------------------------
Eric |
|
| Back to top |
|
|
Henrik Goldman
*nix forums Guru Wannabe
Joined: 26 Mar 2006
Posts: 102
|
| Posted: Sat Jun 10, 2006 8:28 am Post subject:
Re: Hiding symbols in shared library
|
|
|
| Quote: | Once you start playing with symbol visibility you're likely to have
to figure out symbols that are added by the implementation, so +e is
probably a better choice. I highly recommend the "HP-UX Linker and
Library User's Guide" at http://docs.hp.com/en/B2355-90655/index.html.
|
Great thanks! All problems are solved. I read the manual and used +e as you
explained. Now the only global symbols are the ones that I specify and the
unresolved ones.
Here is what I wrote for the g++ frontend linker:
LDFLAGS += -shared -Wl,+e -Wl,A -Wl,+e -Wl,B -Wl,+e -Wl,C ...
-- Henrik |
|
| Back to top |
|
|
Vishwas Pai
*nix forums beginner
Joined: 21 Mar 2006
Posts: 31
|
| Posted: Mon Jun 12, 2006 6:39 am Post subject:
Re: Hiding symbols in shared library
|
|
|
Henrik Goldman wrote:
| Quote: | Once you start playing with symbol visibility you're likely to have
to figure out symbols that are added by the implementation, so +e is
probably a better choice. I highly recommend the "HP-UX Linker and
Library User's Guide" at http://docs.hp.com/en/B2355-90655/index.html.
Great thanks! All problems are solved. I read the manual and used +e as you
explained. Now the only global symbols are the ones that I specify and the
unresolved ones.
Here is what I wrote for the g++ frontend linker:
LDFLAGS += -shared -Wl,+e -Wl,A -Wl,+e -Wl,B -Wl,+e -Wl,C ...
|
Alternatively (instead of multiple -Wl ..) you can pass
all the `ld` options in file (see -c filename in ld(1)).
--vishwas. |
|
| Back to top |
|
|
Dennis Handly
*nix forums beginner
Joined: 28 Jun 2005
Posts: 38
|
| Posted: Sat Jul 15, 2006 4:50 am Post subject:
Re: Hiding symbols in shared library
|
|
|
Henrik Goldman wrote:
: Here is what I wrote for the g++ frontend linker:
: LDFLAGS += -shared -Wl,+e -Wl,A -Wl,+e -Wl,B -Wl,+e -Wl,C ...
Generally you should not separate ld options and their args with separate
-Wls. Combine them: -Wl,+e,A -Wl,+e,B -Wl,+e,C
(Of course you can go crazy by combining them into all one -Wl. ;-)
Note: Typically using tricky ld options like +e and -h is very dangerous for
C++ since it may hide the C++ metadata. All sorts of problems can happen
with aC++. |
|
| Back to top |
|
|
Google
|
|
| Back to top |
|
|
|
|
The time now is Sun Nov 23, 2008 11:22 am | All times are GMT
|
|
Free File Hosting | Mortgage Calculator | Free Credit Report | Loans | Mortgage Calculator
|
|
Copyright © 2004-2005 DeniX Solutions SRL
|
|
|
|
Other DeniX Solutions sites:
Unix/Linux blog |
electronics forum |
medicine forum |
science forum |
|
|
Privacy Policy
|
Powered by phpBB © 2001, 2005 phpBB Group
|
|
FAQ
Search
Memberlist
Usergroups
Register
Profile
Log in to check your private messages
Log in
Forum index
»
*nix
»
HP-UX
