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

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?

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 ).

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

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).

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

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?

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

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

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