[SLUG] Finding .so's path from inside the .so at runtime?

2005-02-24 Thread amos 
Hello,

Is there a standard way for a .so file to find where it was loaded from?

Background:

I ported an ISAPI module from windows to Linux (to connect to Zeus
web server). The original code on Windows relays on the .DLL's ability
to find its path on the disk in order to lookup a configuration file relative
to it.

On Linux I just used an anvironment variable but later I noticed that
the Java Plugin for Mozilla relays on being symbolically-linked
(rather than copied) in order to run, and I suspect that maybe it
needs this in order to find the rest of the files at runtime (e.g. the
runtime class library, the zoneinfo files etc).
I'd like to use the same trick myself.

Currently I think of immitating the ld.so algorithm for finding files
but that could get unreliable if the algorithm changes one day,
and involves duplicating of the work already done by the loader itself.
I'd rather try to get the real info from the dynamic loader.

Any ideas?

Thanks,

--Amos

(BTW - the ISAPI module is Caucho's Resin and is under GPL, the port
is expected to be included in the next release of Resin (3.0.12), and I'll be
happy to provide the patch to anyone who asks).
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Re: [SLUG] Finding .so's path from inside the .so at runtime?

2005-02-24 Thread Ian Wienand 
On Fri, Feb 25, 2005 at 11:17:48AM +1100, [EMAIL PROTECTED] wrote:
 Is there a standard way for a .so file to find where it was loaded from?

from man dl_iterate_phdr 

  The info argument is a structure of the following type:

 struct dl_phdr_info {
   ElfW(Addr)dlpi_addr;  /* Base address of object */
   const char   *dlpi_name;  /* (Null-terminated) name of
object
   const ElfW(Phdr) *dlpi_phdr;  /* Pointer to array of
ELF program headers
for this object */
   ElfW(Half)dlpi_phnum; /* # of items in 'dlpi_phdr' */
 };

  The dlpi_name field is a null-terminated string giving the path-name
  from which the shared object was loaded.

-i
[EMAIL PROTECTED]
http://www.gelato.unsw.edu.au


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Re: [SLUG] Finding .so's path from inside the .so at runtime?

2005-02-24 Thread amos 
Hi,

Thanks. Looks like just what I was looking for. I'll probably
iterate through the output and look for my .so's name in
the dlpi_name base.

It would probably be more accurate to look for a segment
which contains the current function's address, but that'll
require more investigation of the returned data.

Cheers,

--Amos


On Fri, 25 Feb 2005 12:40:11 +1100, Ian Wienand
[EMAIL PROTECTED] wrote:
 On Fri, Feb 25, 2005 at 11:17:48AM +1100, [EMAIL PROTECTED] wrote:
  Is there a standard way for a .so file to find where it was loaded from?
 
 from man dl_iterate_phdr
 
   The info argument is a structure of the following type:
 
  struct dl_phdr_info {
ElfW(Addr)dlpi_addr;  /* Base address of object */
const char   *dlpi_name;  /* (Null-terminated) name of
 object
const ElfW(Phdr) *dlpi_phdr;  /* Pointer to array of
 ELF program headers
 for this object */
ElfW(Half)dlpi_phnum; /* # of items in 'dlpi_phdr' */
  };
 
   The dlpi_name field is a null-terminated string giving the path-name
   from which the shared object was loaded.
 
 -i
 [EMAIL PROTECTED]
 http://www.gelato.unsw.edu.au
 
 

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