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Diffstat (limited to 'ld/PORTING')
| -rw-r--r-- | ld/PORTING | 152 |
1 files changed, 0 insertions, 152 deletions
diff --git a/ld/PORTING b/ld/PORTING deleted file mode 100644 index 8f4125c..0000000 --- a/ld/PORTING +++ /dev/null @@ -1,152 +0,0 @@ - Preliminary Notes on Porting GNU ld - ----------------------------------- - -Before porting ld itself, you will need to port the BFD library; -see ../bfd/PORTING. - -The 'host' is the system a tool runs *on*. -The 'target' is the system a tool runs *for*, i.e. -a tool can read/write the binaries of the target. -Most often, host==target, but ld supports cross-linking -(and to some extent the same ld binary can be used a linker -for multiple target rachitectures). - -Porting to a new host ---------------------- -Pick a name for your host. Call that <host>. -You need to create the file config/mh-<host>. - -Porting to a new target ------------------------ -Pick a name for your target. Call that <target>. -You need to create at least config/mt-<target>. -It should contain - EMUL=<emulation> -An <emulation> controls the "personality" of ld, -such as the default linker script. Usually, the -<emulation> will have teh same name as the <target>, -and you will need to create a new <emulation> (see below). - -You will also need to edit Makefile.in and possible configure.in. -To see how to do that, search for existing examples (e.g. sun3, -sun4, hp300bsd). - -Porting to a new emulation target ---------------------------------- -Pick a name for your target. Call that <emulation>. -Usually, <emulation> and <target> are the same. -You need to create at least <emulation>.sh. -You will also need to edit Makefile.in, -To see how to do that, search for existing examples. - -The file <emulation>.sh defines a set of parameter that -are used to generate the emulation. Its syntax is that -of a (Bourne) shell script, and it is "sourced" by genscripts.sh. - -Writing <emulation.sh> ----------------------- - -Usually, <emulation>.sh contains: - EMULATION_NAME=<emulation> - SCRIPT_NAME=<script> - OUTPUT_FORMAT="<target-name>" - TEXT_START_ADDR=<text_start_addr> - PAGE_SIZE=<page_size> - SEGMENT_SIZE=<segment_size> # If different from PAGE_SIZE. - ARCH=<arch> - -<target-name> - Matches the 'filename' field of the bfd_target you want - to use. (This is a string, and currently the first field.) - For an a.out target, <target-name> matches the TARGETNAME - defined in ../bfd/<target>.c. - -<arch> - The architecture: e.g. m68k, sparc, ... - -<script> - The file <script>.sc-sh is a shell script which when - eveluated (by genscripts.sh) writes a linker script - file to standard output. You may need to write a new - script. If you use the a.out format or something - similar, you can probably set - SCRIPT_NAME=aout - -<text_start_addr> -<page_size> -<segment_size> - These set the shell variables TEXT_START_ADDR, PAGE_SIZE, - and SEGEMNT_SIZE for use by <script>.sc-sh. - If your script doesn't use these variables, you - don't have to define the variables, - For emulations using a.out files, you can get these - values from ../bfd/<target>c. - -In some cases, you may need more more definitions. -For example, if you can't use generic.em, -you may need to add: - TEMPLATE_NAME=<emulation> -and write your own <emulation>.em file. - -Writing a new <script>.sc-sh ----------------------------- - -You may need to write a new script file for your emulation. - -Your script can use the shell variable LD_FLAG, which has the value: -LD_FLAG= when building a script to be used by default -LD_FLAG=n when building a script to be used for ld -n -LD_FLAG=N when building a script to be used for ld -N -LD_FLAG=r when building a script to be used for ld -r -LD_FLAG=u when building a script to be used for ld -Ur - -The variable RELOCATING is only set if relocation is happening -(i.e. unless the linker is invoked with -r). -Thus your script should has an action ACTION -that should only be done when relocating, -express that as: - ${RELOCATING+ ACTION} -In general, this is the case for most assignments, which should look like: - ${RELOCATING+ _end = .} - -Also, you should assign absolute addresses to sections only -when relocating, so: - .text ${RELOCATING+ ${TEXT_START_ADDR}}: - -The forms: - .section { ... } > section -should be: - .section { ... } > ${RELOCATING+ section} - -RELOCATING is set except when LD_FLAG=r or LD_FLAG=u. -CONSTRUCTING is set except when LD_FLAG=u. - -Alignment of the data segments is controlled by the variables -DATA_ALIGNMENT_ (note trailing underscore), DATA_ALIGNMENT_n, -DATA_ALIGNMENT_N, DATA_ALIGNMENT_r, or DTA_ALIGNMENT_u -depending on LD_FLAGS's value. -Normally, the default value works (this is "ALIGN(${SEGMENT_SIZE})" -for the _n, and __ (default) variants; "." for the _N, variant; -and "" for the _r and _u variants). - -Handling -n and -N style binaries in your linker script -------------------------------------------------------- - -The -n linker flag requests the linker to create a binary -with a write-protected text segment, but not demand-pagable (NMAGIC). -Sunos starts the text segment for demand-paged binaries at 0x2020 -and other binaries at 0x2000, since the exec header (0x20 bytes) -is paged in with the text. Some other Unix variants do the same. - -In that case, the <emulation.sh> should define: - -NONPAGED_TEXT_START_ADDR - The text start address to use when linking with -n or -N flags. - -For example, on a sun4: - TEXT_START_ADDR=0x2020 - NONPAGED_TEXT_START_ADDR=0x2000 - -The -N linker flag requests the linker to create a binary -without a write-protected text segment (NMAGIC). -This is like -n, except that the data segment needs not be page-aligned. |