72 lines
3.2 KiB
Plaintext
72 lines
3.2 KiB
Plaintext
The C library of the Genode OS Framework is based on the code of FreeBSD. The
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original code is available at the official FreeBSD website.
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:FreeBSD website: [http://www.freebsd.org]
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Currently, the libc supports the x86_32, x86_64 and ARM architectures. Support
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for other architectures is planned as future addition.
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Usage
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-----
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Before the libc is ready to use, the original FreeBSD source codes must be
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downloaded and integrated with the Genode build system. The tool 'prepare_port'
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automates this task. Please make sure to have Subversion installed. Then issue
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the following command:
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! ./tool/ports/prepare_port libc
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To use the libc in your application, add 'libc' to the 'LIBS' declaration in
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your build-description file. This declaration will make the libc headers
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available for the include path of your target and link the C library. When
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building, make sure that the 'libports' repository is included in your build
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configuration ('<build-dir>/etc/build.conf').
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Limitations
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-----------
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The current version of the C library is not thread-safe. For most string and
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math functions, this is not a problem (as these functions do not modify global
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state) but be careful with using more complex functions such as 'malloc' from
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multiple threads. Also, 'errno' may become meaningless when calling libc
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functions from multiple threads.
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We have left out the following files from the Genode port of the FreeBSD libc:
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:gdtoa libary: 'strtodnrp.c'
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:gen library: 'getosreldate.c'
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:string libary: 'strcoll.c', 'strxfrm.c', 'wcscoll.c', 'wcsxfrm.c'
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:math library: 's_exp2l.c'
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In the ARM version, the following additional files are excluded:
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:libm: 'e_acosl.c', 'e_asinl.c', 'e_atan2l.c', 'e_hypotl.c', 's_atanl.c',
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's_cosl.c', 's_frexpl.c', 's_nextafterl.c', 's_nexttoward.c',
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's_rintl.c', s_scalbnl.c', 's_sinl.c', 's_tanl.c', 's_fmal.c'
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Atomic operation on ARM are not supported. Although these operations are
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defined in 'machine/atomic.h', their original FreeBSD implementations are not
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functional because we do not emulate the required FreeBSD environment (see:
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'sysarch.h'). However, these functions are not a regular part of the libc
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anyway and are not referenced from any other libc code.
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The current back end is quite simplistic and it may help you to revisit the
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current state of the implementation in the 'src/lib/libc' directory. If
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one of the functions in 'dummies.c' is called, you will see an message in your
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debug output:
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! <function-name> called, not yet implemented!
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However, some of the back-end function implemented in the other files have
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dummy semantics but have to remain quiet because they are called from low-level
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libc code.
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Genode-specific additions
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-------------------------
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The back end of the libc is tailored to Genode via a flexible plugin concept.
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This concept enables the combination of a variety of Genode-specific interfaces
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with libc-based programs. For example, one program may want to use Genode's LOG
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service as standard output whereas interactive programs might prefer the use of
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Terminal sessions. Further available (entirely optional) back ends include a
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BSD socket implementation based on the lwIP stack and a VFAT file-system back
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end based on libffat. The interfaces used between plugins and the libc are
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located at 'include/libc-plugin/'.
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