2009-05-18 14:37:41 +02:00
|
|
|
Android Dynamic Linker Design Notes
|
|
|
|
===================================
|
|
|
|
|
|
|
|
Introduction:
|
|
|
|
-------------
|
|
|
|
|
|
|
|
This document provides several notes related to the design of the Android
|
|
|
|
dynamic linker.
|
|
|
|
|
|
|
|
|
|
|
|
Initialization and Termination functions:
|
|
|
|
-----------------------------------------
|
|
|
|
|
|
|
|
The Unix Sys V Binary Interface standard states that an
|
|
|
|
executable can have the following entries in its .dynamic
|
|
|
|
section:
|
|
|
|
|
|
|
|
DT_INIT
|
|
|
|
Points to the address of an initialization function
|
|
|
|
that must be called when the file is loaded.
|
|
|
|
|
|
|
|
DT_INIT_ARRAY
|
|
|
|
Points to an array of function addresses that must be
|
|
|
|
called, in-order, to perform initialization. Some of
|
|
|
|
the entries in the array can be 0 or -1, and should
|
|
|
|
be ignored.
|
|
|
|
|
|
|
|
Note: this is generally stored in a .init_array section
|
|
|
|
|
|
|
|
DT_INIT_ARRAYSZ
|
|
|
|
The size of the DT_INITARRAY, if any
|
|
|
|
|
|
|
|
DT_FINI
|
|
|
|
Points to the address of a finalization function which
|
|
|
|
must be called when the file is unloaded or the process
|
|
|
|
terminated.
|
|
|
|
|
|
|
|
DT_FINI_ARRAY
|
|
|
|
Same as DT_INITARRAY but for finalizers. Note that the
|
|
|
|
functions must be called in reverse-order though
|
|
|
|
|
2011-01-18 18:36:38 +01:00
|
|
|
Note: this is generally stored in a .fini_array section
|
2009-05-18 14:37:41 +02:00
|
|
|
|
|
|
|
DT_FINI_ARRAYSZ
|
|
|
|
Size of FT_FINIARRAY
|
|
|
|
|
|
|
|
DT_PREINIT_ARRAY
|
|
|
|
An array similar to DT_INIT_ARRAY which must *only* be
|
|
|
|
present in executables, not shared libraries, which contains
|
|
|
|
a list of functions that need to be called before any other
|
|
|
|
initialization function (i.e. DT_INIT and/or DT_INIT_ARRAY)
|
2011-12-21 10:03:54 +01:00
|
|
|
in the executable or any of its libraries.
|
2009-05-18 14:37:41 +02:00
|
|
|
|
2011-01-18 18:36:38 +01:00
|
|
|
Note: this is generally stored in a .preinit_array section
|
2009-05-18 14:37:41 +02:00
|
|
|
|
|
|
|
DT_PREINIT_ARRAYSZ
|
|
|
|
The size of DT_PREINIT_ARRAY
|
|
|
|
|
|
|
|
If both a DT_INIT and DT_INITARRAY entry are present, the DT_INIT
|
|
|
|
function must be called before the DT_INITARRAY functions.
|
|
|
|
|
|
|
|
Consequently, the DT_FINIARRAY must be parsed in reverse order before
|
|
|
|
the DT_FINI function, if both are available.
|
|
|
|
|
|
|
|
Note that the implementation of static C++ constructors is very
|
|
|
|
much processor dependent, and may use different ELF sections.
|
|
|
|
|
|
|
|
On the ARM (see "C++ ABI for ARM" document), the static constructors
|
2011-01-18 18:36:38 +01:00
|
|
|
must be called explicitly from the DT_INIT_ARRAY, and each one of them
|
2009-05-18 14:37:41 +02:00
|
|
|
shall register a destructor by calling the special __eabi_atexit()
|
|
|
|
function (provided by the C library). The DT_FINI_ARRAY is not used
|
|
|
|
by static C++ destructors.
|
|
|
|
|
|
|
|
On x86, the lists of constructors and destructors are placed in special
|
|
|
|
sections named ".ctors" and ".dtors", and the DT_INIT / DT_FINI functions
|
2011-01-18 18:36:38 +01:00
|
|
|
are in charge of calling them explicitly.
|
2009-05-18 14:37:41 +02:00
|
|
|
|
2010-01-20 21:36:51 +01:00
|
|
|
|
|
|
|
Debugging:
|
|
|
|
----------
|
|
|
|
|
2013-02-19 20:13:44 +01:00
|
|
|
You can increase the verbosity of debug traces by defining the LD_DEBUG
|
|
|
|
environment variable to a numeric value from 0 to 2 (corresponding to
|
|
|
|
INFO, TRACE, and DEBUG calls in the source). This will only
|
2010-01-20 21:36:51 +01:00
|
|
|
affect new processes being launched.
|
|
|
|
|
|
|
|
By default, traces are sent to logcat, with the "linker" tag. You can
|
|
|
|
change this to go to stdout instead by setting the definition of
|
2011-01-18 18:36:38 +01:00
|
|
|
LINKER_DEBUG_TO_LOG to 0 in "linker_debug.h".
|