Problem with Function Pointers in my Module in Apache 1.3...

The Problem :
I am using a function pointer in my WebServer module to call OpenSSL
function - SSL_get_peer_certificate() from the main Apache process.
The function definition is taken from the OpenSSL Library : libssl.a .
On execution, I get the following error in my Apache Error Log file :
Error: Look up of symbol - SSL_get_peer_certificate failed - Function
not implemented (SSL_get_peer_certificate).

Modules used to build Apache WebServer :
mod_ssl version : 2.8.22-1.3.33
OpenSSL version : 0.9.7d ( openssl-0.9.7e is giving problem while
building on AIX )
Apache version : 1.3.33
AIX version : 4.3 and 5.2
gcc version : 2.95.3

Code :
------------------------------------------------------
void * libssl = NULL;
typedef X509* (*funcptr)(SSL*);
funcptr fptr = NULL;

// Get the handle to main Apache process
libssl = dlopen (NULL, RTLD_NOW | RTLD_GLOBAL | RTLD_MEMBER );
fptr = (funcptr) dlsym(libssl, "SSL_get_peer_certificate");
------------------------------------------------------

Details :
Initially, the problem I faced was that the function symbol
SSL_get_peer_certificate, was getting garbage collected ( During
linking and binding on AIX, any unused or unreferenced symbols are
deleted ). This was the output of nm command on httpd executable :
..SSL_get_peer_certificate T 269039260
... ie .. the function definition was visible only in the Text Section.

Hence, while building Apache, I specifically exported the function
symbol using -u flag with ld. The make command is :
make MFLAGS="EXTRA_LDFLAGS='-uSSL_get_peer_certificate'"

The output of nm command on httpd executable now is :
..SSL_get_peer_certificate T 269039260
SSL_get_peer_certificate D 536993772
SSL_get_peer_certificate d 536993772 12
Now, the function is visible in the Data Section both at global and
local level.

But I am still not able to access the function using the pointer. Same
is the case with accessing the functions in my own module, using a
pointer.

Further Observations :
- If we do a dlsym to get the handle of a function defined inside
Apache Code, there is no such problem.
- There is no problem using function pointers in the rest of our
application.

Has anybody else faced a similar problem? Any pointers or related
links would be of great help.

Thanks in Advance,
Prashant.

Prashant Shetty wrote:
 > Code :
 > ------------------------------------------------------
 > void * libssl = NULL;
 > typedef X509* (*funcptr)(SSL*);
 > funcptr fptr = NULL;
 >
 > // Get the handle to main Apache process
 > libssl = dlopen (NULL, RTLD_NOW | RTLD_GLOBAL | RTLD_MEMBER );
 > fptr = (funcptr) dlsym(libssl, "SSL_get_peer_certificate");
 > ------------------------------------------------------
 >
<...snip...>
 >
 > The output of nm command on httpd executable now is :
 > .SSL_get_peer_certificate T 269039260
 > SSL_get_peer_certificate D 536993772
 > SSL_get_peer_certificate d 536993772 12
 > Now, the function is visible in the Data Section both at global and
 > local level.

Not good enough. -u only prevents garbage collection. The real
question is, is the symbol _exported_? dump -Tv <file> | grep peer
will tell you this. nm and dump -tv are useless when what you need to
examine is the API of the module. You'll need to add an export list
(-bE:<explist>) to your build command.

Otherwise, your dlopen/dlsym usage appears correct.

--
Gary R. Hook
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