This directory contains Genode's dynamic linker (ldso)


Usage
-----

To build a shared library instead of a regular static library, you just need to
declare 'SHARED_LIB = yes' in the library-description file.  When doing so, a
'<libname>.lib.so' file will be generated and installed in the
'<build-dir>/bin/' directory.  For building an executable that uses a shared
library, no special precautions are needed. The build system will automatically
detect the use of shared libraries, concludes that the binary must be
dynamically linked, and will use the correct linker script.  When loading a
dynamically linked program, the dynamic linker 'ldso.lib.so' and all used shared
objects must be loaded as well.

The linker can be configured through the '<config>' node when loading a dynamic
binary. The configuration option 'ld_bind_now="yes"' prompts the linker to
resolve all symbol references on program loading. 'ld_verbose="yes"' outputs
library load information before starting the program.

Configuration snippet:

!<!-- bind immediately, no library informations -->
!<start name="dynamic_binary" ram="1M">
!  <config ld_bind_now="yes" ld_verbose="no">
!  </config>
!</start>

Preloading libraries
--------------------

The dynamic linker supports the preloading of libraries according to its
configuration. The list of libraries must be specified within an '<ld>'
sub node of the configuration:

! <config>
!   ...
!   <ld>
!     <library rom="libc_customization.lib.so"/>
!   </ld>
!   ...
! </config>

Debugging dynamic binaries with GDB stubs
-----------------------------------------

! # go to directory containing the binaries
! cd <build/dir>/bin
!
! # start GDB with binary to debug
! gdb <binary name>
!
! # break in main routine
! b main
!
! # inspect loaded shared libraries
! info sharedlibrary
!
! # load shared symbols of shared libraries (if not already loaded)
! share
!
! # from here you can debug within libraries

:Known issues:

GDB 7.2 has a regression bug in its line information parser. These issue has
been fixed with version 7.3.

Execution of global static constructors
---------------------------------------

The dynamic linker does not implicitely execute global static constructors
(ctors) at the loading time of a program but leaves this up to the loaded
program, which can trigger the execution of the ctors by calling
'Env::exec_static_constructors()'. This gives the program the power over
the point in time for such initializations. However, once a component's
initialization is complete (when 'Component::construct') returned, the linker
checks that static constructors - if present - were executed and aborts
otherwise. This check can be explicitely disabled by specifying the config
attribute 'ld_check_ctors="no"'.
