LinkerConfig
Introduction
Linkerconfig is a program to generate linker configuration based on the runtime environment. Linkerconfig generates one or more ld.config.txt files and some other files under /linkerconfig during init. Linker will read this generated configuration file(s) to find out link relationship between libraries and executable.
Inputs
TODO: explain inputs (e.g. /system/etc/public.libraries.txt, /apex/apex-info-list.xml, ..)
linker.config.json
Linker configuration file can be used to add extra information while linkerconfig
creates linker configuration with the module. This module can be defined as
linker_config
from Soong, and it will be translated as protobuf file at build
time.
A linker configuration file(linker.config.json) is compiled into a protobuf at build time
by conv_linker_config
. You can find the compiled file under <base>/etc/linker.config.pb
.
For example, /apex/com.android.art/etc/linker.config.pb
is a configuration for the com.android.art
APEX.
/system/etc/linker.config.pb
(or its source module system_linker_config
) is special because
its provideLibs
key is generated at build time.
Format
linker.config.json file is in json format which can contain properties as below.
Property Name | Type | Description | Allowed module |
---|---|---|---|
permittedPaths | List | Additional permitted paths | APEX |
visible | bool | Force APEX namespace to be visible from all sections if the value is true | APEX |
provideLibs | List | Libraries providing from the module | System |
requireLibs | List | Libraries required from the module | System |
Example
APEX module
{
"permittedPaths" : [ "/a", "/b/c", "/d/e/f"],
"visible": true
}
System
{
"provideLibs" : [ "a.so", "b.so", "c.so" ],
"requireLibs" : [ "foo.so", "bar.so", "baz.so" ]
}
Outputs
/linkerconfig/ld.config.txt & /linkerconfig/*/ld.config.txt
TODO: a few words about the files
Check ld.config.format.md.
/linkerconfig/apex.libraries.txt
The file describes libraries exposed from APEXes. libnativeloader is the main consumer of this file.
# comment line
jni com_android_foo libfoo_jni.so
public com_android_bar libbar.so:libbaz.so
The file is line-based and each line consists of tag apex_namespace library_list
.
tag
explains whatlibrary_list
is.apex_namespace
is the namespace of the apex. Note that it is mangled likecom_android_foo
for the APEX("com.android.foo").library_list
is colon-separated list of library names.- if
tag
isjni
,library_list
is the list of JNI libraries exposed byapex_namespace
. - if
tag
ispublic
,library_list
is the list of public libraries exposed byapex_namespace
. Here, public libraries are the libs listed in/system/etc/public.libraries.txt.
- if