Norman Feske 4da52517c1 Simpify startup of dynamically linked binaries
This patch removes the component_entry_point library, which used to
proved a hook for the libc to intercept the call of the
'Component::construct' function. The mechansim has several shortcomings
(see the discussion in the associated issue) and was complex. So we
eventually discarded the approach in favor of the explicit handling of
the startup.

A regular Genode component provides a 'Component::construct' function,
which is determined by the dynamic linker via a symbol lookup.
For the time being, the dynamic linker falls back to looking up a 'main'
function if no 'Component::construct' function could be found.

The libc provides an implementation of 'Component::construct', which
sets up the libc's task handling and finally call the function
'Libc::Component::construct' from the context of the appllication task.
This function is expected to be provided by the libc-using application.
Consequently, Genode components that use the libc have to implement the
'Libc::Component::construct' function.

The new 'posix' library provides an implementation of
'Libc::Component::construct' that calls a main function. Hence, POSIX
programs that merely use the POSIX API merely have to add 'posix' to the
'LIBS' declaration in their 'target.mk' file. Their execution starts at
'main'.

Issue #2199
2017-01-13 13:06:52 +01:00
..
2016-11-08 15:26:32 +01:00

This directory contains library description files.  Each '<libname>.mk' file
holds the instruction for building the library '<libname>'. These makefiles are
never used directly but they are called from the build system when required.
When called, the build system passes the following variables:

:'BASE_DIR': This is the base directory of the source tree.

Source codes are specified by setting the 'SRC_CC' and 'SRC_C' variables.
The source code locations must be specified via 'vpath'.
A library can include other libraries by setting the 'LIBS'
variable.

Each '<libname>.mk' file must include the 'lib.mk' role file:

! include $(BASE_DIR)/mk/lib.mk

Libraries implementing one and the same library interface may have specific
implementations for different platforms. Such platform-specific '<libname>.mk'
files should be placed into corresponding subdirectories. For example, the
'linux'-specific implementation of the 'server' library resides in the 'linux/'
subdirectory. The build system automatically searches the right '<libname>.mk'
file by evaluating the 'SPECS' configuration variable. If 'SPECS' is set to
'host linux', the build system will look into the directories './', './host',
and './linux'.