digitalmars.D - Using dlopen/dlsym

Andrei Alexandrescu (24/24) Dec 26 2016 Consider this code:

Nicholas Wilson (4/14) Dec 26 2016 Does auto p = dlsym(hndl, fun.mangleof.ptr);

Andrei Alexandrescu (2/16) Dec 26 2016 No, same result. -- Andrei

Benjiro (3/28) Dec 26 2016 Odd ... Works perfect on Debian ( DMD64 D Compiler v2.071.2 ).
Adam D. Ruppe (7/8) Dec 26 2016 Do dmd -v for verbose output and see what linker flags it is

Mike Wey (5/12) Dec 27 2016 dmd will need to pass "--export-dynamic" to the linker, so that the

Martin Nowak (2/4) Dec 31 2016 Thanks, at least one useful answer out of nine!

Jacob Carlborg (5/27) Dec 27 2016 I tried on Mint 18 and Ubuntu 16.10 with DMD 2.072.2-b1, it worked for m...
Chris Wright (2/3) Dec 27 2016 What DMD version are you using?
Jacob Carlborg (11/33) Dec 27 2016 Although I don't think this is the problem, the correct way to check if
unDEFER (2/2) Dec 27 2016 It works on my Ubuntu 16.04 and dmd v2.071.1
Martin Nowak (13/16) Dec 31 2016 Importing symbols from your executable requires to tell the

Andrei Alexandrescu <SeeWebsiteForEmail erdani.org> writes:

Consider this code:

===========
import core.sys.posix.dlfcn;
extern(C) void fun() {}
void main()
{
     fun();
     void *hndl = dlopen(null, RTLD_LAZY);
     if (!hndl) assert(0);
     auto p = dlsym(hndl, "fun".ptr);
     if (!p)
     {
         import core.stdc.stdio;
         printf("%s\n", dlerror());
     }
}
===========

It works (i.e. outputs nothing) on http://dpaste.dzfl.pl and on 
Vladimir's machine.

On my Mint and Ubuntu machines it outputs:

./test: undefined symbol: fun

I'm building with no flags using dmd. What could be the problem here?


Thanks,

Adnrei

Dec 26 2016

Nicholas Wilson <iamthewilsonator hotmail.com> writes:

On Tuesday, 27 December 2016 at 00:05:39 UTC, Andrei Alexandrescu 
wrote:
 Consider this code:

 ===========
 import core.sys.posix.dlfcn;
 extern(C) void fun() {}
 void main()
 {
     fun();
     void *hndl = dlopen(null, RTLD_LAZY);
     if (!hndl) assert(0);
     auto p = dlsym(hndl, "fun".ptr);

Does auto p = dlsym(hndl, fun.mangleof.ptr);

work any better?

Dec 26 2016

Andrei Alexandrescu <SeeWebsiteForEmail erdani.org> writes:

On 12/26/2016 07:35 PM, Nicholas Wilson wrote:
 On Tuesday, 27 December 2016 at 00:05:39 UTC, Andrei Alexandrescu wrote:
 Consider this code:

 ===========
 import core.sys.posix.dlfcn;
 extern(C) void fun() {}
 void main()
 {
     fun();
     void *hndl = dlopen(null, RTLD_LAZY);
     if (!hndl) assert(0);
     auto p = dlsym(hndl, "fun".ptr);

 Does auto p = dlsym(hndl, fun.mangleof.ptr);

 work any better?

No, same result. -- Andrei

Dec 26 2016

Benjiro <benjiro benjiro.com> writes:

On Tuesday, 27 December 2016 at 00:05:39 UTC, Andrei Alexandrescu 
wrote:
 Consider this code:

 ===========
 import core.sys.posix.dlfcn;
 extern(C) void fun() {}
 void main()
 {
     fun();
     void *hndl = dlopen(null, RTLD_LAZY);
     if (!hndl) assert(0);
     auto p = dlsym(hndl, "fun".ptr);
     if (!p)
     {
         import core.stdc.stdio;
         printf("%s\n", dlerror());
     }
 }
 ===========

 It works (i.e. outputs nothing) on http://dpaste.dzfl.pl and on 
 Vladimir's machine.

 On my Mint and Ubuntu machines it outputs:

 ./test: undefined symbol: fun

 I'm building with no flags using dmd. What could be the problem 
 here?


 Thanks,

 Adnrei

Odd ... Works perfect on Debian ( DMD64 D Compiler v2.071.2 ).

Dec 26 2016

Adam D. Ruppe <destructionator gmail.com> writes:

On Tuesday, 27 December 2016 at 00:05:39 UTC, Andrei Alexandrescu 
wrote:
 I'm building with no flags using dmd.

Do dmd -v for verbose output and see what linker flags it is 
doing. Perhaps you have a configuration difference that is 
causing it not to export the symbol (`fun` isn't marked 
`export`... I don't think that matters on linux but it might on 
some versions or with some configurations).

Dec 26 2016

Mike Wey <mike-wey example.com> writes:

On 12/27/2016 06:02 AM, Adam D. Ruppe wrote:
 On Tuesday, 27 December 2016 at 00:05:39 UTC, Andrei Alexandrescu wrote:
 I'm building with no flags using dmd.

 Do dmd -v for verbose output and see what linker flags it is doing.
 Perhaps you have a configuration difference that is causing it not to
 export the symbol (`fun` isn't marked `export`... I don't think that
 matters on linux but it might on some versions or with some
 configurations).

dmd will need to pass "--export-dynamic" to the linker, so that the 
symbol is actually exported.

-- 
Mike Wey

Dec 27 2016

Martin Nowak <code dawg.eu> writes:

On Tuesday, 27 December 2016 at 18:12:42 UTC, Mike Wey wrote:
 dmd will need to pass "--export-dynamic" to the linker, so that 
 the symbol is actually exported.

Thanks, at least one useful answer out of nine!

Dec 31 2016

Jacob Carlborg <doob me.com> writes:

On 2016-12-27 01:05, Andrei Alexandrescu wrote:
 Consider this code:

 ===========
 import core.sys.posix.dlfcn;
 extern(C) void fun() {}
 void main()
 {
     fun();
     void *hndl = dlopen(null, RTLD_LAZY);
     if (!hndl) assert(0);
     auto p = dlsym(hndl, "fun".ptr);
     if (!p)
     {
         import core.stdc.stdio;
         printf("%s\n", dlerror());
     }
 }
 ===========

 It works (i.e. outputs nothing) on http://dpaste.dzfl.pl and on
 Vladimir's machine.

 On my Mint and Ubuntu machines it outputs:

 ./test: undefined symbol: fun

 I'm building with no flags using dmd. What could be the problem here?

I tried on Mint 18 and Ubuntu 16.10 with DMD 2.072.2-b1, it worked for me.

Which versions of Mint, Ubuntu, dmd, gcc, ldd etc. are you using?

-- 
/Jacob Carlborg

Dec 27 2016

Chris Wright <dhasenan gmail.com> writes:

On Mon, 26 Dec 2016 19:05:39 -0500, Andrei Alexandrescu wrote:
 I'm building with no flags using dmd. What could be the problem here?

What DMD version are you using?

Dec 27 2016

Jacob Carlborg <doob me.com> writes:

On 2016-12-27 01:05, Andrei Alexandrescu wrote:
 Consider this code:

 ===========
 import core.sys.posix.dlfcn;
 extern(C) void fun() {}
 void main()
 {
     fun();
     void *hndl = dlopen(null, RTLD_LAZY);
     if (!hndl) assert(0);
     auto p = dlsym(hndl, "fun".ptr);
     if (!p)
     {
         import core.stdc.stdio;
         printf("%s\n", dlerror());
     }
 }
 ===========

 It works (i.e. outputs nothing) on http://dpaste.dzfl.pl and on
 Vladimir's machine.

 On my Mint and Ubuntu machines it outputs:

 ./test: undefined symbol: fun

 I'm building with no flags using dmd. What could be the problem here?

Although I don't think this is the problem, the correct way to check if 
dlsym was successful is to call dlerror, not check if the result from 
dlsym was null. From the man page:

"Since the value of the symbol could actually be NULL (so that a NULL 
return from dlsym() need not indicate an error), the correct way to test 
for an error is to call dlerror(3) to clear any old error conditions, 
then call dlsym(), and then call dlerror(3) again, saving its return 
value into a variable, and check whether this saved value is not NULL"

-- 
/Jacob Carlborg

Dec 27 2016

unDEFER <undefer gmail.com> writes:

It works on my Ubuntu 16.04 and dmd v2.071.1
But it wants to call dlopen() as core.sys.posix.dlfcn.dlopen().

Dec 27 2016

Martin Nowak <code dawg.eu> writes:

On Tuesday, 27 December 2016 at 00:05:39 UTC, Andrei Alexandrescu 
wrote:
 ./test: undefined symbol: fun

 I'm building with no flags using dmd. What could be the problem 
 here?

Importing symbols from your executable requires to tell the 
linker to create a dynamic symbol table, i.e. using 
--export-dynamic for ld.
We also add that flag by default on many platforms because our 
exception backtraces still rely on the dynamic symbol tables, 
instead of exclusively using dedicated DWARF information.
Combining both effects might lead to confusing behavior.

Also see:

[Issue 11870 – replace dynamic symbol table (--export-dynamic) 
for backtraces](https://issues.dlang.org/show_bug.cgi?id=11870)
https://dlang.org/changelog/2.069.0.html#curl-dynamic-loading

Dec 31 2016

D Programming

C/C++ Programming

Other

digitalmars.D - Using dlopen/dlsym