Should `dlopen` not first search the libraries loaded already like `dllist` ones?

Internals & Design
1

Hi All,

I am trying to search for libc so that I can pass the malloc function to a library.

julia> dlopen("libc")
ERROR: could not load library "libc"
/usr/lib/x86_64-linux-gnu/libc.so: invalid ELF header
Stacktrace:
 [1] #dlopen#3(::Bool, ::Function, ::String, ::UInt32) at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.1/Libdl/src/Libdl.jl:109
 [2] dlopen at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.1/Libdl/src/Libdl.jl:109 [inlined] (repeats 2 times)
 [3] top-level scope at none:0

while dllist gives me a different libc is loaded.

julia> dllist()
28-element Array{AbstractString,1}:
 "linux-vdso.so.1"                                                                  
 "/home/sambit/julia-install/julia-1.1.0/bin/../lib/libjulia.so.1"                  
 "/lib/x86_64-linux-gnu/libdl.so.2"                                                 
 "/lib/x86_64-linux-gnu/librt.so.1"                                                 
 "/lib/x86_64-linux-gnu/libpthread.so.0"                                            
 "/lib/x86_64-linux-gnu/libc.so.6"

Should /lib/x86_64-linux-gnu/libc.so.6 not be loaded by dlopen in the first place?

regards,

Sambit

2

Instead of “libc” you should use “libc.so.6” then it should work.

best regards

Michael

3

Will check that. But that may be a bit platform specific.

regards,

Sambit

4 
julia> dlopen("libc.so.6")
Ptr{Nothing} @0x00007fbe7ec7b400

works. But I am not fully convinced if this is the right approach. Is the libc6 kind of standard on all Unix platforms Julia supports? In that case it’s fine.

regards,

Sambit

5

I would assume libc6 is kind of default. Libc 2-5 were released in 90s.

regards,

Sambit

6

On my laptop with Lubuntu 16.04 libc.so.6 is a link to libc-2.23.so.

best regards

Michael

7

@mwolff,

There is libc as POSIX standard library version and there glibc which is the GNU libc version. The libc-2.23.so is the glibc version. We cannot rely on that one much as that may vary from system to system.

glibc-2.x is all libc6.

sambit@ubutubu:/lib/x86_64-linux-gnu$ ls -l *libc*
-rwxr-xr-x 1 root root 2030544 Apr 17  2018 libc-2.27.so
...
lrwxrwxrwx 1 root root      12 Apr 17  2018 libc.so.6 -> libc-2.27.so

regards,

Sambit

8

As far as I know, a new version of libc only changes the link from libc.so.6 to the new version. Or you can create your own local link to the latest version.

best regards

Michael