.. comment SPDX-License-Identifier: CC-BY-SA-4.0 .. comment: Copyright (c) 2017 Chris Johns .. comment: All rights reserved. RTEMS Symbols ============= .. index:: Tools, rtems-syms The RTEMS Symbols (:program:`rtems-syms`) command is an RTEMS Tool to generate symbol tables used by the RTEMS Runtime Loader (RTL). The symbol table is loaded at run time with the exported base kernel image's symbols so dynamically loaded code can link to them. The RTEMS Runtime Loader supports embedding of a symbol table in the base kernel image or loading the symbol table at runtime. Embedding the table requires linking the symbol table with the base image and runtime loading loads the table using the dynamic loader when RTEMS is running. .. sidebar:: *Filtering Symbols* Currently there is no filtering of symbols loaded into the symbol table. This means all base kernel image symbols are present in the symbol table when only a sub-set of the symbols may be referenced. Embedding the symbol table creates self contained images. A target may not have any external media, for example RTEMS tests, or there is a requirement to avoid the overhead of maintaining matching the symbol table files and kernel base images. Embedding the symbol table requires a 2-pass link process making the application's build system more complicated as well as lengthing the build time. A dynamically loadable symbol table is simpler to create however the symbol table and the kernel base image must match or the behaviour is undefined. The :program:`rtems-syms` command is run against the base kernel image and the generated symbol table is installed on to the target hardware and loaded before any other modules. The symbol table object file contains a constructor that is called after being loaded and that code registers the symbol table. Symbol Table ------------ The symbol table is an ELF object file in the target's ELF format and is built using the target's RTEMS C compiler. The :program:`rtems-syms` command searches for the C compller under the prefix this command is installed under or the system path. If this fails the option ``-c`` or ``--cc`` to override the path to the compiler can be used. The :program:`rtems-syms` command loads the base kernel image's ELF file reading the symbols then creates a temporary C file it compiles using the RTEMS C compiler. The command automatically detects the architecture from the base kernel image's ELF file. The option ``-E`` or ``--exec-prefix`` can be used to override the executable prefix used. It is important to supply suitable C compiler flags (cflags) so the symbol table can be linked or loaded. 2-Pass Linking -------------- 2-Pass linking is used to embed a symbol table in a base kernel image. The first link pass is a normal RTEMS kernel link process. The link output is passed to the :program:`rtems-syms` command and the ``-e`` or ``--embed`` option is used. The symbol table object file created by :program:`rtems-syms` is added to the linker command used in the first pass to create the second pass. The address map will change between the first pass and second pass without causing a problem, the symbol table embedded in the second link pass will adjust the symbol addresses to match. Command ------- :program:`rtems-syms` [options] kernel .. option:: -V, --version Display the version information and then exit. .. option:: -v, --verbose Increase the verbose level by 1. The option can be used more than once to get more detailed trace and debug information. .. option:: -w, --warn Enable build warnings. This is useful when debugging symbol table generation. .. option:: -k, --keep Do not delete temporary files on exit, keep them. .. option:: -e, --embed Create a symbol table that can be embedded in the base kernel image using a 2-pass link process. .. option:: -S, --symc Specify the symbol's C source file. The defautl is to use a temporary file name. .. option:: -o, --output Specify the ELF output file name. .. option:: -m, --map Create a map file using the provided file name. .. option:: -C, --cc Specify the C compile executable file name. The file can be absolute and no path is search or relative and the environment's path is searched. .. option:: -E, --exec-prefix Specify the RTEMS tool prefix. For example for RTEMS 4.12 and the SPARC architecture the prefix is ``sparc-rtems4.12``. .. option:: -c, --cflags Specify the C compiler flags used to build the symbol table with. These should be the same or compatible with the flags used to build the RTEMS kernel. .. option:: -?, -h Reort the usage help. Examples -------- Create a dynamlically loaded symbol table for the ``minimum.exe`` sample program for the ``i386/pc686`` BSP: .. code-block:: shell $ rtems-syms -o ms.o i386-rtems4.12/c/pc686/testsuites/samples/minimum/minimum.exe $ file ms.o ms.o: ELF 32-bit LSB relocatable, Intel 80386, version 1 (SYSV), not stripped Run the same command, this time create a map file: .. code-block:: shell $ rtems-syms -o ms.o -m ms.map i386-rtems4.12/c/pc686/testsuites/samples/minimum/minimum.exe $ head -10 ms.map RTEMS Kernel Symbols Map kernel: i386-rtems4.12/c/pc686/testsuites/samples/minimum/minimum.exe Globals: No. Index Scope Type SHNDX Address Size Name 0 931 STB_GLOBAL STT_OBJECT 11 0x0012df08 4 BSPBaseBaud (minimum.exe) 1 1124 STB_GLOBAL STT_OBJECT 11 0x0012d894 4 BSPPrintkPort (minimum.exe) 2 836 STB_GLOBAL STT_FUNC 1 0x00104b00 302 BSP_dispatch_isr (minimum.exe) 3 1156 STB_GLOBAL STT_FUNC 1 0x001082d0 92 BSP_install_rtems_shared_irq_handler (minimum.exe) 4 876 STB_GLOBAL STT_FUNC 1 0x00106500 138 BSP_outch (minimum.exe) Run the same command with a raise verbose level to observe the stages the command performs: .. code-block:: shell $ rtems-syms -vvv -o ms.o i386-rtems4.12/c/pc686/testsuites/samples/minimum/minimum.exe RTEMS Kernel Symbols 4.12.a72a462adc18 kernel: i386-rtems4.12/c/pc686/testsuites/samples/minimum/minimum.exe cache:load-sym: object files: 1 cache:load-sym: symbols: 1043 symbol C file: /tmp/rld--X7paaa.c symbol O file: ms.o execute: i386-rtems4.12-gcc -O2 -c -o ms.o /tmp/rld--X7paaa.c execute: status: 0