Re: dlsym() on implicit loaded symbols

[Roland Dittel]

Am 16.07.2006 um 14:33 schrieb Simon 'corecode' Schubert:


Roland Dittel wrote:
We have a issue with dlsym() on symbols imported by a library that 
was loaded with dlopen(). Our code loads the libssl with dlopen() 
and then do a dlsym() on several symbols. This works for all 
symbols exported by libssl itself but fails for symbols exported by 
libcrypto.

[..]

  func = dlsym(handle, "CRYPTO_set_id_callback");


you have to use RTLD_DEFAULT instead of handle, but I agree, this is 
not in conformance with SUSv3:


That's it. Thank you very much.

Roland



   The dlsym() function shall search for the named symbol in all 
objects loaded automatically as a result of loading the object 
referenced by handle (see dlopen()). Load ordering is used in dlsym() 
operations upon the global symbol object. The symbol resolution 
algorithm used shall be dependency order as described in dlopen().


   The RTLD_DEFAULT and RTLD_NEXT flags are reserved for future use.

Note "in all objects loaded automatically".  Good catch!

cheers
 simon

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Re: dlsym() on implicit loaded symbols

[Roland Dittel]

Simon 'corecode' Schubert wrote:

Roland Dittel wrote:

Hi all,

We have a issue with dlsym() on symbols imported by a library that was 
loaded with dlopen(). Our code loads the libssl with dlopen() and then 
do a dlsym() on several symbols. This works for all symbols exported 
by libssl itself but fails for symbols exported by libcrypto. Libssl 
is dynamically linked to libcrypto and should be loaded for libssl. I 
did a truss and the FreeBSD loader loads libcrypto but does not read 
anything from the file pointer.


could you post a sample code fragment which illustrates the problem you 
are seeing?


Sure, attached is a simple example that tries to load the symbol 
CRYPTO_set_id_callback from a libssl handle. The symbol is located in 
libcrypto and NOT in libssl. Because libssl is dynamically linked to 
libcrypto I would expect the loader is able to find the symbol, but 
that's not the case on freebsd.




cheers
 simon

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dlsym() on implicit loaded symbols

[Roland Dittel]

Hi all,

We have a issue with dlsym() on symbols imported by a library that was  
loaded with dlopen(). Our code loads the libssl with dlopen() and then  
do a dlsym() on several symbols. This works for all symbols exported by  
libssl itself but fails for symbols exported by libcrypto. Libssl is  
dynamically linked to libcrypto and should be loaded for libssl. I did  
a truss and the FreeBSD loader loads libcrypto but does not read  
anything from the file pointer.


This is the truss output:

access("/prod/lib/fbsd-i386/libssl.so",0) = 0 (0x0)
open("/prod/lib/fbsd-i386/libssl.so",0x0,027757760020) = 3 (0x3)
fstat(3,0xbfbfe010)  = 0 (0x0)
fstatfs(0x3,0xbfbfde30)  = 0 (0x0)
read(3,"ELF


 ",4096)  = 4096 (0x1000)
mmap(0x0,229376,(0x5)PROT_READ|PROT_EXEC,(0x20002)MAP_NOCORE|MAP_PRIVATE 
,3,0x0) = 674971648 (0x283b4000)

mprotect(0x283e7000,4096,(0x7)PROT_READ|PROT_WRITE|PROT_EXEC) = 0 (0x0)
mprotect(0x283e7000,4096,(0x5)PROT_READ|PROT_EXEC) = 0 (0x0)
mmap(0x283e8000,16384,(0x3)PROT_READ|PROT_WRITE,(0x12)MAP_FIXED|MAP_PRIV 
ATE,3,0x33000) = 675184640 (0x283e8000)

close(3) = 0 (0x0)
access("/prod/lib/fbsd-i386/libcrypto.so.0.9.8",0) = 0 (0x0)
open("/prod/lib/fbsd-i386/libcrypto.so.0.9.8",0x0,05005664564) = 3 (0x3)
fstat(3,0xbfbfdfe0)  = 0 (0x0)
close(3) = 0 (0x0)
mmap(0x0,5528,(0x3)PROT_READ|PROT_WRITE,(0x1000)MAP_ANON,-1,0x0) =  
675201024 (0x283ec000)

munmap(0x283ec000,5528)  = 0 (0x0)


On solaris, linux and irix the same code works fine and the libcrypto  
symbols are implicit loaded and usable. Does anyone know why FreeBSD  
behaves differently that other Unixes?


Thanks,
Roland

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