Print Page - [SOLVED] How to call a FPC compiled shared library under Alpine?

Programming => Operating Systems => Linux => Topic started by: rarnu on June 11, 2021, 07:36:43 pm

Title: [SOLVED] How to call a FPC compiled shared library under Alpine?
Post by: rarnu on June 11, 2021, 07:36:43 pm

I'm now using Alpine Linux for some development. I find that the shared library compiled with FPC can't be loaded by other programs.

here's my library's code:

Code: Pascal [Select][+]

library mylib;
{$mode objfpc}{$H+}
uses
  Classes, SysUtils;
 
function add(x: integer; y: integer): integer; cdecl;
begin
  Result := x + y;
end;
 
exports
  add;
 
begin
end.
 

These code compiled by command:

Code: Text [Select][+]

$ fpc mylib.lpr -FL/lib/libc.musl-x86_64.so.1
 

There is no "ld-linux-x86-64.so.2" in Alpine Linux, even glibc is also not included. Only musl-libc can be used.

and here's my app for calling the lib:

Code: Pascal [Select][+]

program host;
{$mode objfpc}{$H+}
 
uses
  Classes, SysUtils, dynlibs;
 
type
  TAdd = function (x: integer; y: integer): integer; cdecl;
 
var
  libPath: string;
  lib: TLibHandle;
  mAdd: TAdd;
begin
  libPath:= ExtractFilePath(ParamStr(0)) + 'libmylib.so';
  lib := loadLibrary(libPath);
  mAdd := TAdd(GetProcAddress(lib, 'add'));
  WriteLn(mAdd(1, 2));
end;
 

These code compiled by command:

Code: Pascal [Select][+]

$ fpc host.lpr -FL/lib/libc.musl-x86_64.so.1
 

now I get "libmylib.so" and "host" files, and I try to run "host", it crashed with the message:

Code: Pascal [Select][+]

An unhandled exception occurred at $00007F4E99259B40:
EAccessViolation: 
  $00007F4E99259B40
  $0000000000422D84
  $0000000000422D84
  $0000000000422D84
  $0000000000422D84
  $0000000000422D84
  $0000000000422D84
  $0000000000422D84
  $0000000000422D84
  $0000000000422D84
  $0000000000422D84
  $0000000000422D84
  $0000000000422D84
  $0000000000422D84
  $0000000000422D84
  $0000000000422D84
  $0000000000422D84
 
Segmentation fault
 

I can't solve the problem with the given message, needs help.

And I have also tried, write these code with C and compiled with gcc, it works fine!!

I want to know the reason and how to make it work.

Help me please. thank you.

Title: Re: How to call a FPC compiled shared library under Alpine?
Post by: MarkMLl on June 11, 2021, 10:00:03 pm

Quote from: rarnu on June 11, 2021, 07:36:43 pm

There is no "ld-linux-x86-64.so.2" in Alpine Linux, even glibc is also not included. Only musl-libc can be used.

That's pretty weird, since generally speaking ld-linux-something.so is a prerequisite for a standard .elf file.

Without volunteering that I have a solution but to keep the ball rolling, what is the output of this command

$ readelf -d `which gcc`

MarkMLl

Title: Re: How to call a FPC compiled shared library under Alpine?
Post by: Fred vS on June 11, 2021, 10:00:43 pm

Hello Ramu.

Not sure it could help but what about to use for export code in "mylib" ?:

Code: Pascal [Select][+]

...
exports
  add name 'add';
 

And for fpc command line (added "-fPIC") ?:

Code: Bash [Select][+]

$ fpc mylib.lpr -fPIC -FL/lib/libc.musl-x86_64.so.1

And in "host" program, to localize the error ?:

Code: Pascal [Select][+]

...
 lib := loadLibrary(libPath);
 if lib = nilhandle then 
  WriteLn(libpath + ' not loaded')
else
begin
  mAdd := TAdd(GetProcAddress(lib, 'add'));
  if assigned(mAdd)
  WriteLn(mAdd(1, 2)) else
  WriteLn('mAdd  not assigned')
end;

Title: Re: How to call a FPC compiled shared library under Alpine?
Post by: rarnu on June 12, 2021, 03:02:25 am

Quote from: MarkMLl on June 11, 2021, 10:00:03 pm

Quote from: rarnu on June 11, 2021, 07:36:43 pm
There is no "ld-linux-x86-64.so.2" in Alpine Linux, even glibc is also not included. Only musl-libc can be used.

That's pretty weird, since generally speaking ld-linux-something.so is a prerequisite for a standard .elf file.

Without volunteering that I have a solution but to keep the ball rolling, what is the output of this command

$ readelf -d `which gcc`

MarkMLl

Thank you MarkMLI, here is my command result:

Code: Pascal [Select][+]

Dynamic section at offset 0xf49f8 contains 21 entries:
  Tag        Type                         Name/Value
 0x0000000000000001 (NEEDED)             Shared library: [libc.musl-x86_64.so.1]
 0x000000000000000c (INIT)               0x403000
 0x000000000000000d (FINI)               0x479e6f
 0x0000000000000019 (INIT_ARRAY)         0x4f31d0
 0x000000000000001b (INIT_ARRAYSZ)       112 (bytes)
 0x000000006ffffef5 (GNU_HASH)           0x4002c8
 0x0000000000000005 (STRTAB)             0x401090
 0x0000000000000006 (SYMTAB)             0x400328
 0x000000000000000a (STRSZ)              1097 (bytes)
 0x000000000000000b (SYMENT)             24 (bytes)
 0x0000000000000015 (DEBUG)              0x0
 0x0000000000000003 (PLTGOT)             0x4f5b98
 0x0000000000000002 (PLTRELSZ)           3144 (bytes)
 0x0000000000000014 (PLTREL)             RELA
 0x0000000000000017 (JMPREL)             0x4015b8
 0x0000000000000007 (RELA)               0x4014e0
 0x0000000000000008 (RELASZ)             216 (bytes)
 0x0000000000000009 (RELAENT)            24 (bytes)
 0x0000000000000018 (BIND_NOW)           
 0x000000006ffffffb (FLAGS_1)            Flags: NOW
 0x0000000000000000 (NULL)               0x0
 
 

Title: Re: How to call a FPC compiled shared library under Alpine?
Post by: rarnu on June 12, 2021, 03:08:25 am

Quote from: Fred vS on June 11, 2021, 10:00:43 pm

Hello Ramu.

Not sure it could help but what about to use for export code in "mylib" ?:

Code: Pascal [Select][+][-]
...
exports
add name 'add';

And for fpc command line (added "-fPIC") ?:

Code: Bash [Select][+][-]
$ fpc mylib.lpr -fPIC -FL/lib/libc.musl-x86_64.so.1

And in "host" program, to localize the error ?:

Code: Pascal [Select][+][-]
...
lib := loadLibrary(libPath);
if lib = nilhandle then
WriteLn(libpath + ' not loaded')
else
begin
mAdd := TAdd(GetProcAddress(lib, 'add'));
if assigned(mAdd)
WriteLn(mAdd(1, 2)) else
WriteLn('mAdd not assigned')
end;

Thank you Fred, I have tried your code.

I find the crash happens when calling "loadLibrary", I also tried "SafeLoadLibrary" still not work.

And then I tried the C code like:

Code: C [Select][+]

// add.h
int add(int x, int y);
 

Code: C [Select][+]

// add.c
#include "add.h"
 
int add(int x, int y) {
  return x + y;
}
 

and compiled with command

Code: Text [Select][+]

$ gcc -shared -o libmylib.so add.c
 

Now I get a library named "libmylib.so" and this library can be loaded by FPC's "loadLibrary" and it works fine.

what's the difference between C's library and FPC's library?

Title: Re: How to call a FPC compiled shared library under Alpine?
Post by: PierceNg on June 12, 2021, 04:28:55 am

Quote from: rarnu on June 11, 2021, 07:36:43 pm

There is no "ld-linux-x86-64.so.2" in Alpine Linux, even glibc is also not included. Only musl-libc can be used.

There is a libc-compat package on Alpine. All it does is to create a link to musl-libc. I've used this to run Ubuntu-compiled FPC programs on Alpine.

Try installing libc-compat package and re-run your program. If that fails, try rebuilding your shared library and program on Ubuntu, say, then run on Alpine with libc-compat installed.

If still doesn't work, glibc is also available as an Alpine package.

Title: Re: How to call a FPC compiled shared library under Alpine?
Post by: rarnu on June 12, 2021, 05:49:28 am

Quote from: PierceNg on June 12, 2021, 04:28:55 am

Quote from: rarnu on June 11, 2021, 07:36:43 pm
There is no "ld-linux-x86-64.so.2" in Alpine Linux, even glibc is also not included. Only musl-libc can be used.

There is a libc-compat package on Alpine. All it does is to create a link to musl-libc. I've used this to run Ubuntu-compiled FPC programs on Alpine.

Try installing libc-compat package and re-run your program. If that fails, try rebuilding your shared library and program on Ubuntu, say, then run on Alpine with libc-compat installed.

If still doesn't work, glibc is also available as an Alpine package.

Thank you PierceNg, I have tried to install a compat lib of glibc. here's the results:

with official libc6-compat, FPC library can't load, and the app with mysql(needs official libmysqlclient.so) inside works fine.
with 3rd-party glibc 2.33, FPC library works fine, but the libmysqlclient.so can't load.

I want my FPC library and mysql both work, but ...

Title: Re: How to call a FPC compiled shared library under Alpine?
Post by: Fred vS on June 12, 2021, 06:09:59 am

Hello Rarnu.

What do you get with this console command to check the methods of the fpc library?

Code: Bash [Select][+]

$ nm -D libmylib.so

Title: Re: How to call a FPC compiled shared library under Alpine?
Post by: rarnu on June 12, 2021, 07:09:05 am

Quote from: Fred vS on June 12, 2021, 06:09:59 am

Hello Rarnu.

What do you get with this console command to check the methods of the fpc library?

Code: Bash [Select][+][-]
$ nm -D libmylib.so

yep, I think this is the key point. FPC's library's exported methods is different with C's

Code: Pascal [Select][+]

00000000000470a0 T add
 

FPC exports only one method, but C's library exports more:

Code: Pascal [Select][+]

                 w _ITM_deregisterTMCloneTable
                 w _ITM_registerTMCloneTable
                 w __cxa_finalize
                 w __deregister_frame_info
                 w __register_frame_info
0000000000001175 T _fini
0000000000001000 T _init
000000000000113f T add
 

here are "_init" and "_fini", I think my lib must have them exported, but how?

Title: Re: How to call a FPC compiled shared library under Alpine?
Post by: Fred vS on June 12, 2021, 02:57:11 pm

Quote

here are "_init" and "_fini", I think my lib must have them exported, but how?

Hum, I think you will need a guru.

Maybe you can try to add those "_init" and "_fini" in your lib and export it.

https://docs.oracle.com/cd/E88353_01/html/E37854/u-fini-9e.html

Sorry, I dont use Alpine so I cannot test.

Fre;D

Title: [Solved] How to call a FPC compiled shared library under Alpine?
Post by: rarnu on June 13, 2021, 04:51:36 am

Thank you all for the help. I find the final solution.

first of all, official libc6-compat must be installed into Alpine. Do NEVER install the 3rd-party glibc, it will override ld-linux-x86-64.so.2 and break other packages in Alpine because almost all packages in Alpine are built by musl-libc, and the original ld-linux-x86-64.so.2 is a symlink from libc.musl-x86_64.so .

so my solution is to remove the dependency of ld-linux-x86-64.so.2 from my lib.

use the command for make a like.res:

Code: Pascal [Select][+]

$ fpc -Cn mylib.lpr
 

It will generate the link.res and ppas.sh. Open link.res, find "INPUT (ld-linux-x86-64.so.2)" and then remove it. run ppas.sh for build a shared library.

Code: Pascal [Select][+]

$ ./ppas.sh
 

here can get a libmylib.so without ld-linux-x86-64.so.2 required. use "readelf -d libmylib.so" to check it.

And one more step is to remove "dynlibs" from host app. In Alpine can't use that.

I added a compile switch to it：

Code: Pascal [Select][+]

uses Classes, SysUtils {$IFNDEF ALPINE}, dynlibs {$ENDIF};
 

and compile host app with the command:

Code: Pascal [Select][+]

$ fpc -dALPINE host.lpr
 

well, the problem is solved. :D

Title: Re: [SOLVED] How to call a FPC compiled shared library under Alpine?
Post by: MarkMLl on June 13, 2021, 09:53:54 am

Congratulations on fixing it and thanks for keeping us updated.

Since what you did involved changing FPC-generated files (i.e. wasn't just a fix to your Alpine configuration) I suggest it would be worthwhile posting it on Mantis so that the core developers are aware... not so much because they're expected to do support what can only be described as a minority platform but in case this could usefully be handled in a more general and widely-applicable way.

MarkMLl

Title: Re: [Solved] How to call a FPC compiled shared library under Alpine?
Post by: Fred vS on June 13, 2021, 12:57:28 pm

Quote from: rarnu on June 13, 2021, 04:51:36 am

Code: Pascal [Select][+][-]
uses Classes, SysUtils {$IFNDEF ALPINE}, dynlibs {$ENDIF};

well, the problem is solved. :D

Wow, congrats!

May I ask you how do you load the library if you dont use dynlibs (LoadLibrary) ?
Do you use instead "external" (and then no dynamic loading)?

Fre;D

Title: Re: [Solved] How to call a FPC compiled shared library under Alpine?
Post by: rarnu on June 13, 2021, 06:09:26 pm

Quote from: Fred vS on June 13, 2021, 12:57:28 pm

Wow, congrats!

May I ask you how do you load the library if you dont use dynlibs (LoadLibrary) ?
Do you use instead "external" (and then no dynamic loading)?

Fre;D

I have not found the way to use a library dynamically. Just the simplest code:

Code: Pascal [Select][+]

program host;
 
{$mode objfpc}{$H+}
 
uses classes, Sysutils{$IFNDEF ALPINE}, dynlibs {$ENDIF};
 
function add(x: integer; y: integer): integer; cdecl; external 'mylib';
 
begin
  writeln(add(1, 2));
end.

and execute it by:

Code: Pascal [Select][+]

$ LD_LIBRARY_PATH=. ./host
 

or make libmylib.so a symlink to "/usr/lib" is also worked.

And, I have tried something else to make it dynamic but failed. here is the code:

Code: Pascal [Select][+]

program host;
 
{$mode objfpc}{$H+}
 
uses Classes, Sysutils, dl;
 
type
  TAdd = function (x: Integer; y: Integer): Integer; cdecl;
 
var
  libPath: string;
  lib: Pointer;
  mAdd: TAdd;
begin
  libPath:= ExtractFilePath(ParamStr(0)) + 'libmylib.so';
  lib := dlopen(PChar(libPath), RTLD_NOW);
  mAdd := TAdd(dlsym(lib, 'add'));
  writeln(mAdd(1, 2));
end.
 

this code works on my ubuntu and manjaro. But on Alpine it crashes when calling "dlopen" and no solution now.

on Alpine, even the C code with "dlopen" is also not work. Strange...

Title: Re: [Solved] How to call a FPC compiled shared library under Alpine?
Post by: Fred vS on June 13, 2021, 06:31:55 pm

Quote from: rarnu on June 13, 2021, 06:09:26 pm

Code: Pascal [Select][+][-]
program host;

{$mode objfpc}{$H+}

uses Classes, Sysutils, dl;

type
TAdd = function (x: Integer; y: Integer): Integer; cdecl;

var
libPath: string;
lib: Pointer;
mAdd: TAdd;
begin
libPath:= ExtractFilePath(ParamStr(0)) + 'libmylib.so';
lib := dlopen(PChar(libPath), RTLD_NOW);
mAdd := TAdd(dlsym(lib, 'add'));
writeln(mAdd(1, 2));
end.

this code works on my ubuntu and manjaro. But on Alpine it crashes when calling "dlopen" and no solution now.

on Alpine, even the C code with "dlopen" is also not work. Strange...

Hum, strange indeed.

In dl.pas, "dlopen" has this code:

Code: Pascal [Select][+]

function dlopen(Name : PChar; Flags : longint) : Pointer; cdecl; external libdl;  

And libdl is defined as:

Code: Pascal [Select][+]

const
{$ifdef BSD}   // dlopen is in libc on FreeBSD.
  LibDL = 'c';
{$else}
  {$ifdef HAIKU}
    LibDL = 'root';
  {$else}
    LibDL = 'dl';
  {$endif}
{$endif}         

Could you check if there is a /usr/lib/libdl.so in your system?

Maybe you will have to create a symlink that point to the installed libdl.so.x of your system.

[EDIT] Other maybe: It could be that in Alpine dlopen is part of a other library than libdl.so.x .

If it is the case, imho, fpc should add a {$ifdef ALPINE} define (like ~~MarkMLI proposed~~ somebody insinuated).

Fre;D

Title: Re: [SOLVED] How to call a FPC compiled shared library under Alpine?
Post by: engkin on June 13, 2021, 08:00:23 pm

Can you share the ppas.sh and link.res produced by FPC on your system?

Title: Re: [Solved] How to call a FPC compiled shared library under Alpine?
Post by: MarkMLl on June 13, 2021, 08:29:21 pm

Quote from: Fred vS on June 13, 2021, 06:31:55 pm

If it is the case, imho, fpc should add a {$ifdef ALPINE} define (like MarkMLI proposed).

I didn't propose anything! Keep my name out of it!! :-)

But more seriously... noting OP's most recent comment, I was tinkering with something a year or so ago which had a frontend/backend architecture connected in /both/ /directions/ by explicitly-loaded dynamic entry points, and having problems on 64-bit Debian. There might, possibly, be a fundamental OS problem lurking, since 32-bit was OK... I didn't report it as a problem pending more investigation and making sure I had exactly the same FPC and library versions.

MarkMLl

Title: Re: [Solved] How to call a FPC compiled shared library under Alpine?
Post by: rarnu on June 13, 2021, 09:05:49 pm

Quote from: Fred vS on June 13, 2021, 06:31:55 pm

Could you check if there is a /usr/lib/libdl.so in your system?

Maybe you will have to create a symlink that point to the installed libdl.so.x of your system.

[EDIT] Other maybe: It could be that in Alpine dlopen is part of a other library than libdl.so.x .

If it is the case, imho, fpc should add a {$ifdef ALPINE} define (like MarkMLI proposed).

There is no "libdl.so" or something like that in Alpine, and even no so file contains the dlopen function.

I have use these command to find:

Code: Pascal [Select][+]

# cd /
# find . - name "*.so.*" | xargs echo | xargs nm
 

But I find that there is a "libdl.a" under /usr/lib, and I tried this:

Code: Pascal [Select][+]

program host;
 
{$mode objfpc}{$H+}
{$linklib /usr/lib/libdl.a}
 
uses classes, Sysutils;
 
function dlopen(Name : PChar; Flags : longint) : Pointer; cdecl; external;
function dlsym(Lib : Pointer; Name : Pchar) : Pointer; cdecl; external;
 
type
  TAdd = function (x: Integer; y: Integer): Integer; cdecl;
 
var
  libPath: string;
  lib: Pointer;
  mAdd: TAdd;
begin
  libPath:= ExtractFilePath(ParamStr(0)) + 'libmylib.so';
  lib := dlopen(PChar(libPath), 2);
  mAdd := TAdd(dlsym(lib, 'add'));
  writeln(mAdd(1, 2));
end.
 

still crash when calling dlopen. It seems that dlopen is not contains in that static library (many many libraries in Alpine has no symbol exported, seems stripped).

and the same C code is here, can't work for the same reason

Code: C [Select][+]

#include <stdio.h>
#include <dlfcn.h>
 
#define LIB_PATH "./libmylib.so"
 
typedef int (*add) (int, int);
 
int main() {
  void* handle = dlopen(LIB_PATH, RTLD_NOW);
  add mAdd = (add)dlsym(handle, "add");
  int n = mAdd(1, 2);
  printf("%d\n", n);
  return 0;
}
 

build executable with:

Code: Pascal [Select][+]

$ gcc host.c -ldl
 

the command executed successfully and generated a.out .

Then, I use ldd for checking the libraries, both FPC & C executables returns the same:

Code: Pascal [Select][+]

/lib/ld-musl-x86_64.so.1 (0x7f6e73691000)
libc.musl-x86_64.so.1 => /lib/ld-musl-x86_64.so.1 (0x7f6e73691000)
 

checked ld-musl-x86_64.so.1 and no dlopen in it. :o

Title: Re: [SOLVED] How to call a FPC compiled shared library under Alpine?
Post by: rarnu on June 13, 2021, 09:10:51 pm

Quote from: engkin on June 13, 2021, 08:00:23 pm

Can you share the ppas.sh and link.res produced by FPC on your system?

yes, attached.

Title: Re: [SOLVED] How to call a FPC compiled shared library under Alpine?
Post by: rarnu on June 13, 2021, 09:21:55 pm

And up to now, I have recompiled FPC 3.3.1 from SVN under Alpine 3.12

But the "dynamic load" problem is still.

Title: Re: [SOLVED] How to call a FPC compiled shared library under Alpine?
Post by: Fred vS on June 13, 2021, 09:53:57 pm

Hello.

I am not (yet) a Alpine guru, but there it seems that dlopen is in package libtool:
https://pkgs.alpinelinux.org/contents?file=&path=&name=libtool&branch=edge&repo=main&arch=x86

Quote

/usr/share/libtool/loaders/dlopen.c

Title: Re: [SOLVED] How to call a FPC compiled shared library under Alpine?
Post by: Fred vS on June 13, 2021, 10:23:25 pm

Re-hello.

I think that dlopen() is in libltdl.so library.

https://pkgs.alpinelinux.org/package/edge/main/x86/libltdl

Maybe you may create a a symlink /usr/lib/libdl.so > /usr/lib/libltdl.so (or where is the library).

Title: Re: [SOLVED] How to call a FPC compiled shared library under Alpine?
Post by: engkin on June 13, 2021, 11:03:00 pm

In reply #4 you indicated that the problem is in the library generated by FPC because a gcc generated library did work:

Quote from: rarnu on June 12, 2021, 03:08:25 am

Now I get a library named "libmylib.so" and this library can be loaded by FPC's "loadLibrary" and it works fine.

what's the difference between C's library and FPC's library?

Can you share the output of:

Code: Text [Select][+]

gcc -v -shared -o libmylib.so add.c

and the assembly files generated from FPC when you add -al switch.

Edit:
I noticed from the files you shared the code is stripped. Probably it is a good idea to deactivate stripping for now:

Code: Text [Select][+]

...
/usr/bin/strip --discard-all --strip-debug libmylib.so
...

Also, while it probably will not work, try to remove the initialization call:

Quote

/usr/bin/ld -b elf64-x86-64 -m elf_x86_64 -init FPC_SHARED_LIB_START -fini FPC_LIB_EXIT -soname libmylib.so -shared -L. -o libmylib.so -T link4764.res

Title: Re: [SOLVED] How to call a FPC compiled shared library under Alpine?
Post by: rarnu on June 14, 2021, 05:05:48 am

Quote from: engkin on June 13, 2021, 11:03:00 pm

In reply #4 you indicated that the problem is in the library generated by FPC because a gcc generated library did work:
Quote from: rarnu on June 12, 2021, 03:08:25 am
Now I get a library named "libmylib.so" and this library can be loaded by FPC's "loadLibrary" and it works fine.

what's the difference between C's library and FPC's library?

Can you share the output of:
Code: Text [Select][+][-]
gcc -v -shared -o libmylib.so add.c

and the assembly files generated from FPC when you add -al switch.

Edit:
I noticed from the files you shared the code is stripped. Probably it is a good idea to deactivate stripping for now:
Code: Text [Select][+][-]
...
/usr/bin/strip --discard-all --strip-debug libmylib.so
...

Also, while it probably will not work, try to remove the initialization call:
Quote
/usr/bin/ld -b elf64-x86-64 -m elf_x86_64 -init FPC_SHARED_LIB_START -fini FPC_LIB_EXIT -soname libmylib.so -shared -L. -o libmylib.so -T link4764.res

Thank you engkin, the problem of static load is solved by remove ld-linux-x86-64.so.2 from link.res.

and as you say, remove FPC's init and fini will be more friendly for C callers. I will do that then.

result of command "gcc -v -shared -o libmylib.so add.c" is here:

Code: Pascal [Select][+]

Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-alpine-linux-musl/9.3.0/lto-wrapper
Target: x86_64-alpine-linux-musl
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Title: Re: [SOLVED] How to call a FPC compiled shared library under Alpine?
Post by: rarnu on June 14, 2021, 05:10:35 am

Quote from: Fred vS on June 13, 2021, 10:23:25 pm

Re-hello.

I think that dlopen() is in libltdl.so library.

https://pkgs.alpinelinux.org/package/edge/main/x86/libltdl

Maybe you may create a a symlink /usr/lib/libdl.so > /usr/lib/libltdl.so (or where is the library).

Yes, there is a "lt_dlopen" in libltdl.so, in "ltdl.h" there are some exports:

Code: C [Select][+]

LT_SCOPE lt_dlhandle lt_dlopen          (const char *filename);           
LT_SCOPE lt_dlhandle lt_dlopenext       (const char *filename);        
LT_SCOPE lt_dlhandle lt_dlopenadvise    (const char *filename,  lt_dladvise advise);          
LT_SCOPE void *     lt_dlsym            (lt_dlhandle handle, const char *name);
LT_SCOPE const char *lt_dlerror         (void);                                
LT_SCOPE int        lt_dlclose          (lt_dlhandle handle);             
 

here is my C code with ltdl:

Code: C [Select][+]

#include <stdio.h>
#include <ltdl.h>
 
#define LIB_PATH "./libmylib.so"
 
typedef int (*add) (int, int);
 
int main() {
  lt_dlinit();
  lt_dlhandle handle = lt_dlopen(LIB_PATH);
  add mAdd = (add)lt_dlsym(handle, "add");
  int n = mAdd(1, 2);
  printf("%d\n", n);
  return 0;
}
 

compiled with:

Code: C [Select][+]

$ gcc host.c -lltdl
 

if the so is compiled by C, it works, and if not, it crashes.

Title: Re: [SOLVED] How to call a FPC compiled shared library under Alpine?
Post by: rarnu on June 14, 2021, 08:36:37 am

Again, thanks for all helps. Now I find the final worked solution.

here all the code must be compiled under Alpine, no other linux.

the lib's code:

Code: Pascal [Select][+]

library mylib;
 
{$mode objfpc}{$H+}
 
uses Classes, Sysutils;
 
function add(x: integer; y: integer): integer; cdecl;
begin
  Exit(x + y);
end;
 
exports
  add;
 
end.
 

compile it with command:

Code: Pascal [Select][+]

$ fpc -Cn mylib.lpr
 

remove "ld-linux-x86-64.so.2" in link.res or linkxxx.res

open "ppas.sh" and change the /usr/bin/ld line to:

Code: Pascal [Select][+]

/usr/bin/ld -b elf64-x86-64 -m elf_x86_64 -soname libmylib.so   -shared  -L. -o libmylib.so -T link.res
 

now execute ppas.sh and get the libmylib.so

-------------------------------------------------------------------------

here's my host app's code:

Code: Pascal [Select][+]

program host;
 
{$mode objfpc}{$H+}
 
{$linklib ltdl}
{$linklib c}
 
uses classes, Sysutils;
 
const
  LIB_PATH = './libmylib.so';
 
function lt_dlinit(): integer; cdecl; external;
function lt_dlopen(const filename : PChar) : Pointer; cdecl; external;
function lt_dlsym(Lib : Pointer; const name : Pchar) : Pointer; cdecl; external;
 
type
  TAdd = function (x: Integer; y: Integer): Integer; cdecl;
 
var
  r: integer;
  lib: Pointer;
  mAdd: TAdd;
begin
  lt_dlinit();
  lib := lt_dlopen(LIB_PATH);
  mAdd := TAdd(lt_dlsym(lib, 'add'));
  writeln(mAdd(1, 2));
end.
 

compile it with command:

Code: Pascal [Select][+]

$ fpc -Cn host.lpr
 

open "ppas.sh" and change the param "--dynamic-linker" from "ld-linux-x86-64.so.2" to "ld-musl-x86_64.so.1"

now execute ppas.sh and get host executable.

-------------------------------------------------------------------------

that's all, now I can run host to load libmylib.so dynamically.

and the previous way for static load is also worked.

Thanks you all, a lot.

Title: Re: [SOLVED] How to call a FPC compiled shared library under Alpine?
Post by: Fred vS on June 14, 2021, 01:43:38 pm

Hello Rarnu.

Wow, congrats and thanks for your perseverance (I love 'no giving-up' people').

Your last post should be transferred into a fpc wiki page.

Fre;D

Title: Re: [SOLVED] How to call a FPC compiled shared library under Alpine?
Post by: MarkMLl on June 14, 2021, 03:08:13 pm

Quote from: Fred vS on June 14, 2021, 01:43:38 pm

Wow, congrats and thanks for your perseverance (I love 'no giving-up' people').

I agree. However I think there's a lesson to be learned here: some of the initial problems were caused by a demi-borked system, and assuming that the distro maintainers are competent that can only have been caused by a part-successful installation of an "alien" package.

Assuming that's correct, I'd mention that it's the second problem of this nature in a week: I'd suggest that however much we are repelled by the "string and chewinggum" implementation of Docker it really is quite serviceable at providing a sandbox in which slightly-suspect apps can be run.

MarkMLl

Lazarus

Programming => Operating Systems => Linux => Topic started by: rarnu on June 11, 2021, 07:36:43 pm