diff options
Diffstat (limited to 'ld')
| -rw-r--r-- | ld/PORTING | 153 |
1 files changed, 121 insertions, 32 deletions
@@ -1,26 +1,105 @@ -Some incomplete notes about porting GNU ld ------------------------------------------ + Preliminary Notes on Porting GNU ld + ----------------------------------- -Before porting ld itself, you will need to port the BFD library. +Before porting ld itself, you will need to port the BFD library; +see ../bfd/PORTING. -We tarlk about the 'host' system as the machine and software -nevironment where ld runs (generates an execuitble *on*), -while the 'target' is the machine ld generates an executable *for*. +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). -Doing a 'host' port means working around broken or missing -include files or libraries. ... +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). -Writing a new script script ---------------------------- +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 @@ -39,25 +118,35 @@ The forms: should be: .section { ... } > ${RELOCATING+ section} -Old Makefile comments (re-write - FXIME!) ------------------------------------------ - -# The .xn script is used if the -n flag is given (write-protect text).. -# Sunos starts the text segment for demand-paged binaries at 0x2020 -# and other binaries at 0x2000, since the exec header is paged in -# with the text. Some other Unix variants do the same. -# For -n and -N flags the offset of the exec header must be removed. -# This sed script does this if the master script contains -# a line of the form ".text 0xAAAA BLOCK(0xBBBB):" - the -# output will contain ".text 0xBBBB:". (For Sunos AAAA=2020 and BBBB=2000.) -.x.xn: - sed -e '/text/s/\.text .* BLOCK(\([^)]*\)):/.text \1:/' < $< >$*.xn - -# The .xN script is used if the -N flag is given (don't write-protect text). -# This is like -n, except that the data segment need not be page-aligned. -# So get rid of commands for page-alignment: We assume these use ALIGN -# with a hex constant that end with 00, since any normal page size is be -# at least divisible by 256. We use the 00 to avoid matching -# anything that tries to align of (say) 8-byte boundaries. -.xn.xN: - sed -e '/ALIGN/s/ALIGN( *0x[0-9a-fA-F]*00 *)/./' < $< >$*.xN +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. |