macOS Static Libraries

From Free Pascal wiki

English (en)

macOSlogo.png

This article applies to macOS only.

See also: Multiplatform Programming Guide


Overview

Note-icon.png

Note: Dynamic libraries are also known as dynamic shared libraries, shared objects, or dynamically linked libraries.
Static libraries are also known as static archive libraries and static linked shared libraries.

Most of an application's functionality is implemented in libraries of executable code. When an application's source code is compiled into object code and linked with a static library, the object code and library code that the application uses is copied into the executable file that is loaded into memory in its entirety at launch time. The kind of library that becomes part of an application's executable is known as a static library. Static libraries are collections or archives of object files.

There are two important factors which determine the performance of applications: their launch times and their memory footprints. Reducing the size of an executable file and minimizing its memory use once launched make an application launch faster and use less memory. Using dynamic libraries instead of static libraries reduces the executable file size of an application. Dynamic libraries also allow applications to delay loading libraries with special functionality until they’re needed instead of loading them at launch time. This feature contributes further to reduced launch times and efficient memory use. Another reason to use dynamic libraries is so that you can share code among multiple applications thereby saving the memory (and to a lesser extent nowadays, disk space) that would otherwise be used for multiple copies of the library code.

There are, however, some advantages to statically linking libraries with an executable instead of dynamically linking them. The most significant advantage is that the application can be certain that all its libraries are present and that they are the correct version. Static linking of libraries also allows the application to be contained in a single executable file, simplifying distribution and installation. Also with static linking, only those parts of the library that are directly and indirectly referenced by the target executable are included in the executable. With dynamic libraries, the entire library is loaded, as it is not known in advance which functions will be used by the application. Whether this advantage is significant in practice depends on the structure of the library.

Library extensions and prefixes

Operating System Dynamic library Static library Library prefix
FreeBSD .so .a lib
macOS .dylib .a n/a
Linux .so .a lib
Windows .dll .lib n/a

The library prefix column indicates how the names of the libraries are resolved and created. Under macOS, the library name will always have the lib prefix when it is created. So if you create a dynamic library called test, this will result in the file libtest.dynlib. When importing routines from shared libraries, it is not necessary to give the library prefix or the filename extension.

Example FPC static library

Note-icon.png

Tip: If you use "cdecl", FPC ensures that your function completely adheres to all ABI requirements (naming, parameter passing, etc). If you don't, then you are on your own.

test.pas:

{$mode objfpc} {$H+}


// Note this is a unit and not a library
unit test;

interface 

uses
  // needed for UpperCase
  SysUtils;     

implementation

// library subroutine
function cvtString(strIn : string) : PChar; Cdecl;
begin
  cvtString := PChar(UpperCase(strIn));
end;

end.

Compile:

 fpc test.pas

which produces an object file named test.o which we will now convert into a static library archive named libtest.a using the libtool command line utility:

 libtool -static -o libtest.a test.o

Example FPC application to use FPC static library

statlibdemo.pas:

{$mode objfpc} {$H+}

// Link in our static library
// - note the prefix (lib) and extension (.a) are not necessary
{$LinkLib test}

program statlibdemo;

// Declare our function
function cvtString(strIn : string) : PChar; Cdecl; External Name 'cvtString';

begin
  WriteLn(cvtString('hello world'));
end.

Compile:

 fpc statlibdemo.pas

which unexpectedly produces:

Free Pascal Compiler version 3.3.1 [2020/04/20] for x86_64
Copyright (c) 1993-2020 by Florian Klaempfl and others
Target OS: Darwin for x86_64
Compiling staticlibdemo.pas
Assembling (pipe) staticlibdemo.s
Linking staticlibdemo
Undefined symbols for architecture x86_64:
  "_cvtString", referenced from:
      _PASCALMAIN in staticlibdemo.o
ld: symbol(s) not found for architecture x86_64
An error occurred while linking 
staticlibdemo.pas(11,34) Error: Error while linking
staticlibdemo.pas(11,34) Fatal: There were 1 errors compiling module, stopping
Fatal: Compilation aborted
Error: /usr/local/bin/ppcx64 returned an error exitcode

What happened? Why wasn't our library function cvtString found? Let's look for our function in the test.o object file by running the objdump command line utility:

$ objdump -d test.o
test.o:	file format Mach-O 64-bit x86-64

Disassembly of section __TEXT,__text:
_TEST_$$_CVTSTRING$ANSISTRING$$PCHAR:
       0:	55 	pushq	%rbp
       1:	48 89 e5 	movq	%rsp, %rbp
       4:	48 8d 64 24 80 	leaq	-128(%rsp), %rsp
       9:	48 89 7d f8 	movq	%rdi, -8(%rbp)
       d:	48 8b 7d f8 	movq	-8(%rbp), %rdi
      11:	e8 00 00 00 00 	callq	0 <_TEST_$$_CVTSTRING$ANSISTRING$$PCHAR+0x16>
      16:	48 c7 45 88 00 00 00 00 	movq	$0, -120(%rbp)
      1e:	48 8d 55 d8 	leaq	-40(%rbp), %rdx
      22:	48 8d 75 98 	leaq	-104(%rbp), %rsi
      26:	bf 01 00 00 00 	movl	$1, %edi
      2b:	e8 00 00 00 00 	callq	0 <_TEST_$$_CVTSTRING$ANSISTRING$$PCHAR+0x30>
      30:	48 89 c7 	movq	%rax, %rdi
      33:	e8 00 00 00 00 	callq	0 <_TEST_$$_CVTSTRING$ANSISTRING$$PCHAR+0x38>
      38:	48 63 d0 	movslq	%eax, %rdx
      3b:	48 89 55 90 	movq	%rdx, -112(%rbp)
      3f:	83 f8 00 	cmpl	$0, %eax
      42:	75 22 	jne	34 <_TEST_$$_CVTSTRING$ANSISTRING$$PCHAR+0x66>
      44:	48 8b 75 f8 	movq	-8(%rbp), %rsi
      48:	48 8d 7d 88 	leaq	-120(%rbp), %rdi
      4c:	e8 00 00 00 00 	callq	0 <_TEST_$$_CVTSTRING$ANSISTRING$$PCHAR+0x51>
      51:	48 8b 45 88 	movq	-120(%rbp), %rax
      55:	48 83 f8 00 	cmpq	$0, %rax
      59:	75 07 	jne	7 <_TEST_$$_CVTSTRING$ANSISTRING$$PCHAR+0x62>
      5b:	48 8b 05 00 00 00 00 	movq	(%rip), %rax
      62:	48 89 45 f0 	movq	%rax, -16(%rbp)
      66:	e8 00 00 00 00 	callq	0 <_TEST_$$_CVTSTRING$ANSISTRING$$PCHAR+0x6b>
      6b:	48 8d 7d f8 	leaq	-8(%rbp), %rdi
      6f:	e8 00 00 00 00 	callq	0 <_TEST_$$_CVTSTRING$ANSISTRING$$PCHAR+0x74>
      74:	48 8d 7d 88 	leaq	-120(%rbp), %rdi
      78:	e8 00 00 00 00 	callq	0 <_TEST_$$_CVTSTRING$ANSISTRING$$PCHAR+0x7d>
      7d:	48 8b 45 90 	movq	-112(%rbp), %rax
      81:	48 83 f8 00 	cmpq	$0, %rax
      85:	74 0f 	je	15 <_TEST_$$_CVTSTRING$ANSISTRING$$PCHAR+0x96>
      87:	e8 00 00 00 00 	callq	0 <_TEST_$$_CVTSTRING$ANSISTRING$$PCHAR+0x8c>
      8c:	48 c7 45 90 00 00 00 00 	movq	$0, -112(%rbp)
      94:	eb d0 	jmp	-48 <_TEST_$$_CVTSTRING$ANSISTRING$$PCHAR+0x66>
      96:	48 8b 45 f0 	movq	-16(%rbp), %rax
      9a:	48 89 ec 	movq	%rbp, %rsp
      9d:	5d 	popq	%rbp
      9e:	c3 	retq

Aha! Our function name has been well and truly mangled. It is obvious we need to use the mangled name TEST_$$_CVTSTRING$ANSISTRING$$PCHAR (omit the underscore as the linker will automatically add it) rather than the unmangled cvtString. Our example application now looks like:

{$mode objfpc} {$H+}

// Link in our static library
// - note the prefix (lib) and extension (.a) are not necessary
{$LinkLib test}

program statlibdemo;

// Declare our function
function cvtString(strIn : string) : PChar; Cdecl; External Name 'TEST_$$_CVTSTRING$ANSISTRING$$PCHAR';

begin
  WriteLn(cvtString('hello world'));
end.

Compile:

 fpc statlibdemo.pas

which again dashes our hopes and produces:

Free Pascal Compiler version 3.3.1 [2020/04/20] for x86_64
Copyright (c) 1993-2020 by Florian Klaempfl and others
Target OS: Darwin for x86_64
Compiling staticlibdemo.pas
Assembling (pipe) staticlibdemo.s
Linking staticlibdemo
Undefined symbols for architecture x86_64:
  "_SYSUTILS_$$_UPPERCASE$ANSISTRING$$ANSISTRING", referenced from:
      _TEST_$$_CVTSTRING$ANSISTRING$$PCHAR in libtest.a(test.o)
ld: symbol(s) not found for architecture x86_64
An error occurred while linking 
staticlibdemo.pas(11,34) Error: Error while linking
staticlibdemo.pas(11,34) Fatal: There were 1 errors compiling module, stopping
Fatal: Compilation aborted
Error: /usr/local/bin/ppcx64 returned an error exitcode

Unfortunately we are missing the object file for the UpperCase function which was pulled in from the FPC SysUtils unit. What to do? Simply add the SysUtils unit to the the Uses clause of the application. Our example application now looks like:

{$mode objfpc} {$H+}

// Link in our static library
// - note the prefix (lib) and extension (.a) are not necessary
{$LinkLib test}

program statlibdemo;

// Needed for linking in the UpperCase function
Uses
  SysUtils;

// Declare our function
function cvtString(strIn : string) : PChar; Cdecl; External Name 'TEST_$$_CVTSTRING$ANSISTRING$$PCHAR';

begin
  WriteLn(cvtString('hello world'));
end.

Third time lucky, compile:

 fpc statlibdemo.pas

Run:

$ ./statlibdemo
HELLO WORLD

Example C static library

myfunc1.c

#include <stdio.h>

void myfunc1() 
  {
  printf("This is my func1!\n");
  }

myfunc2.c

#include <ctype.h>

int myfunc2(int c) 
  {
  c = toupper(c);
  return(c);
  }

Compile:

Note-icon.png

Note: If you do not specify the minimum macOS version, the C compiler will compile for your current operating system version, but your Free Pascal Compiler will compile for 10.5 (fpc 3.0.4) or 10.8 (fpc 3.3.1) by default.

cc -c -mmacosx-version-min=10.8 myfunc1.c myfunc2.c

which produces object files named myfunc1.o and myfunc2.o which we will now convert into a static library archive named libmyfuncs.a using the libtool command line utility:

libtool -static -o libmyfuncs.a myfunc1.o myfunc2.o

Example FPC application to use C static library

statlibdemo.pas:

{$mode objfpc}
{$linklib myfuncs}

procedure myfunc1; cdecl; external;
function myfunc2(c : integer) : integer; cdecl; external;

begin
  myfunc1;

  write('This is my func2 - Before: "b"  ');
  writeLn('After : ' + '"' + chr(myfunc2(ord('b'))) + '"');
end.

Compile:

fpc statlibdemo.pas

Run:

$ ./statlibdemo
This is my func1!
This is my func2 - Before: "b"  After : "B"

If you need to check whether your external routines have been linked into the final application, you can use the objdump command line utility:

$ objdump -d staticlibdemo | grep -A13 ^_myfunc
_myfunc1:
100000830:	55 	pushq	%rbp
100000831:	48 89 e5 	movq	%rsp, %rbp
100000834:	48 83 ec 10 	subq	$16, %rsp
100000838:	48 8d 3d 7f 44 02 00 	leaq	148607(%rip), %rdi
10000083f:	b0 00 	movb	$0, %al
100000841:	e8 e6 3d 02 00 	callq	146918 <dyld_stub_binder+0x10002462c>
100000846:	89 45 fc 	movl	%eax, -4(%rbp)
100000849:	48 83 c4 10 	addq	$16, %rsp
10000084d:	5d 	popq	%rbp
10000084e:	c3 	retq
10000084f:	90 	nop

_myfunc2:
100000850:	55 	pushq	%rbp
100000851:	48 89 e5 	movq	%rsp, %rbp
100000854:	48 83 ec 10 	subq	$16, %rsp
100000858:	89 7d fc 	movl	%edi, -4(%rbp)
10000085b:	8b 7d fc 	movl	-4(%rbp), %edi
10000085e:	e8 29 3e 02 00 	callq	146985 <dyld_stub_binder+0x10002468c>
100000863:	89 45 fc 	movl	%eax, -4(%rbp)
100000866:	8b 45 fc 	movl	-4(%rbp), %eax
100000869:	48 83 c4 10 	addq	$16, %rsp
10000086d:	5d 	popq	%rbp
10000086e:	c3 	retq
10000086f:	90 	nop

If you don't care for the assembly language, you can also use the nm command line utility:

nm staticlibdemo | grep myfunc
0000000100000830 T _myfunc1
0000000100000850 T _myfunc2

See also