I want to get the section (at least its address) of a symbol in the object file using linker script. I watched the list of builtin functions but there is nothing like that. Does linker script can tell us the section where the variable is located?
Related
I want to use the suggestion made in de GNU linker manual page 40, i.e. INPUT (subr.o), thus specifying object members in a script file.
Eventually I want to specify all the object members of my program that the linker has to use.
The script file looks like this (only the files parts is shown)
SEARCH_DIR(../lib)
STARTUP(boot.o)
ENTRY(_start)
GROUP (libkernel.a libkflib.a)
INPUT (
lowcore.o
init.o
kfalloc.o
kflog.o
kfprintf.o
)
The linker replies with:
attempt to open boot.o failed
attempt to open ../lib/boot.o failed
m68k-rtems4.11-ld: cannot find boot.o
I have specified the search path, the libraries and a list of object members; the object members are definitly in the libraries.
I was expection the linker to look for object members in the working directory and if not there using the search path and libraries.
Obviously there is something wrong but I cannot figure it out.
Suggestions are welcome in order to achieve the desired way of linking: specifying all objects to link an not more than that.
Thanks
Ben
You have misread the manual:
INPUT(file file ...)
The INPUT command directs the linker to include the named files in the link,
as though they were named on the command line.
...
In case a sysroot prefix is configured, and the filename starts with the / character,
and the script being processed was located inside the sysroot prefix, the
filename will be looked for in the sysroot prefix. Otherwise, the linker will
try to open the file in the current directory. If it is not found, the linker
will search through the archive library search path. See the description of
-L in Command Line Options.
If you use INPUT (-lfile), ld will transform the name to libfile.a, as with
the command line argument -l.
...
GROUP(file file ...)
The GROUP command is like INPUT, except that the named files should all be
archives, and they are searched repeatedly until no new undefined references
are created.
STARTUP(filename)
The STARTUP command is just like the INPUT command, except that filename will
become the first input file to be linked, as though it were specified first on the command line
Or perhaps you have read some other documentation that is in error.
You have got wrong the impression that command GROUP(libboo.a...) is complementary to INPUT(foo.o...)
and STARTUP(bar.o), with the effect that files bar.o, foo.o... will be searched for in archives
libboo.a... and - if found - will be extracted from the archives and added to the linkage.
INPUT(foo.o) has the same effect as specifying foo.o on the linker
commandline except that if not found in the current directory it will be searched
for in the same way that a static library specified with the -l option would be, with any SEARCH_DIR(path)
commands in the linker script having the same influence as commandline options
-Lpath.
STARTUP(bar.o) has the same effect as specifying bar.o first in the linker
commandline.
GROUP(libboo.a...) has the same effect as the commandline options
--start-group -lboo.a... --end-group
again with any SEARCH_DIR(path) commands actiing like -Lpath.
INPUT(foo.o) and STARTUP(bar.o) are unconnected with GROUP(libboo.a...), just as in the commandline options:
bar.o --start-group -lboo.a... --end-group foo.o
bar.o and foo.o are an input files unconnected with --start-group -lboo.a... --end-group.
The linker never looks inside static libraries for an input object file that it otherwise
fails to find.
So this command:
INPUT (
lowcore.o
init.o
kfalloc.o
kflog.o
kfprintf.o
)
in your linker script requires the linker to find those object files in the current
directory or in ../lib, and they are not there. Similarly for STARTUP(boot.o). Hence
the linkage errors.
Those object files aren't there, but static libraries libkernel.a and libkflib.a are,
and you tell us they contain all all those object files as members. In that case
you simply don't need:
INPUT (
lowcore.o
init.o
kfalloc.o
kflog.o
kfprintf.o
)
because the linker will search static libraries to find object files that
provide definitions of any symbols for which definitions are called for
by references within object files that it has already linked. You don't have to
tell it to.
But to give the linker any reason to search a static library at all you
must have told it to link some object file that refers to some undefined symbol(s)
before it considers the static library.
That's the reason why, on the commandline, you must place object files before the
libraries to which they refer and it is why, in a self-contained linker script, if you
add libraries to the linkage with GROUP(libboo.a...) or with INPUT (-lboo...),
you must also specify an object file to be linked first, with a STARTUP
command.
So while your failing INPUT command is unnecessary and can just be
deleted, your failing STARTUP(boot.o) must remain, to initiate
any linkage. And must not fail.
To make STARTUP(boot.o) succeed, you have to put the object file boot.o
itself in a place where the script will tell the linker to look for it,
either the current directory or ../lib. Presumably, the current directory.
And when you do that, it becomes pointless to have boot.o remain as a member
of one your static libraries, since it can't be linked from within one. Best
delete it from whichever libary you have it in. Leaving it there is similar
to putting the main function of a program into one of the libraries you
will link it with.
Is it possible to use a linker script or mapfile to rename a symbol?
I'm trying to adapt some code written in a mix of C++ and Fortran so that it will work with more than one Fortran compiler - on Linux. It is currently written for the Solaris Studio compiler with the option for case-sensitivity enabled. I'd like to handle variations in Fortran symbol name mangling automatically (such as from the Makefile).
It does appear to be possible to create aliases so, a linker script containing:
C_Function_ = c_function;
will sort-of work. Unfortunately, adding the -T option to reference this script causes some other change in behaviour and I get errors due to libdl.so.2/librt.so.1 not being found. Is there some sort of default linker script that I need to include or something? I've tried with both bfd and gold linkers on Linux.
You cannot really rename symbols, but you can define aliases to existing symbols like
PROVIDE(c_function = C_function_);
...
in a linker script.
If you pass this linker script with the -T option to ld, it will replace the original (default) linker script. If you rather want to have the linker script extend the default, pass it without the -T option (just like you would with an additional object file).
This way, everything should work as expected.
The point is to generate a hex without main function using IAR linker - xlink?
This code should be loaded into the RAM of RL78 MCU.
A quick Google search of iar generate hex from library brought me to this document, "Creating an Absolutely Placed Library", as a first result. It has all the information you need, plus some information on using a CRC for consistency checking. The document is for the IAR EWRX variant, but the concepts should all be the same.
The basic process is to compile your library as an executable, but without a main() function in it. You'll need to set your library configuration under General -> Library Options to None. You can also setup your file conversion settings at this point.
Since you don't have a main() function for a program entry point, you will need to create an entry function to call the IAR C runtime initialization function, __iar_data_init2(), and then set the linker to use this function as the entry point (which can be found under Linker Options -> Library Options).
When building a library, all the symbols will be preserved until the final link step for the application using it, but since you are building this as an executable, it is important that the symbols you want to keep have the __root keyword, or under Linker -> Extra Options you can specify --no-remove to keep all symbols.
In the next step, you need to use isymexport to export the symbols that you want. You will need a file to direct the tool what to export. In the example, they have a file that just contains the following:
show lib_*
show __checksum*
This will direct the tool to export all symbols beginning with lib_ and all symbols beginning with __checksum. They note that __iar_data_init2() should not be exported, as this would cause conflicts with the application that ultimately will use this code. You invoke the tool like so:
isymexport <path to .out file> <path to output from tool> --edit <path to file created above>
Now you should have the output from isymexport and the library file that you were looking for. For the application using this library, you'll need to add the output from isymexport as a library under Linker -> Library, and in your application, you'll need to call your entry function in the library before you attempt to use any of the library's symbols.
This should be the information you need to generate a library that lives in a hex file and can be loaded separately, as well as how to use that library. The referenced document has a lot more detail, so if it is available at that link (or can be found elsewhere by title) it will be a better reference than my summary here.
I'm using IAR toolchain to compile few source files and then link generated .o files.
However, I'm running into linking errors like below:
Error[Li005]: no definition for "main" [referenced from cmain.o(rt7M_tl.a)]
Error[Lc036]: no block or place matches the
pattern "ro code section .intvec in vector_table_M.o(rt7M_tl.a)"
As I understand, ILINK linker is trying to link object files as an executable image and in the process adding dependencies from standard libraries[ i.e looking for main() and interrupt vector table ].
What I'm looking for :
How to configure linker to not to add these system-library dependencies like main/start/interrupt-vector-table etc. ?
How to configure linker to output a non-executable image from bunch of object files - if that at all is possible ?
You can think of this non-executable image sort of configuration-table image which will be put in persistent memory to be read/write by main application image.
If you tell the linker that you don't have an entry point with the command line option '--no_entry' you will get rid of the reference to main and the .intvec data.
However you do need to tell the linker what it should keep.
--keep and/or __root can help you with that.
How to write function at particular memory location in flash memory? Is there any directive for that? Do i need particular linker?
If you are using keil ide you can place a function at a specific address using .ARM.__at_address as the section name. To place the function add at 0x20000, specify:
int add(int n1,int n2) __attribute__((section(".ARM.__at_0x20000")));
int add(int n1,int n2)
{
return n1+n2;
}
Do you use the keil toolchain?
If yes, perhaps http://www.keil.com/support/docs/359.htm helps.
Edit:
The .obj file is generated by the compiler. I am not sure what you mean with 'how can i configure .obj file'.
The linker mentioned above takes the obj files, links them together and places code and variables.
You should start with a project which compiles and links without errors.
Then you have:
- Some c files. One of them with your function.
- A linkfile with the settings for the linker.
- A makefile or some kind of batchfile which calls compiler and linker with the necessary arguments.
If you have that, you can look into the m51 file for the name of the symbol for your function.
The m51 file is a textfile generated by the lx51 linker with interesting information about which symbols are there and what the linker has done with them.
The keil documentation for the linker I mentioned says: The compiler creates a symbol name for the function using the following format: ?PR?function_name?file_name.
This means: You will find the names of all functions of your project in the m51 file. If your function is in file file_x and named func_x. The symbol name will be PR?func_x?file_x
In http://www.keil.com/support/man/docs/lx51/lx51_segments.htm you can find some information about the usage of the SEGMENTS directive of the lx51 linker. According to that:
SEGMENTS (PR?func_x?file_x(C:0x1234))
should place your function to address 0x1234 in code memory.
Actually I have no keil toolchain. Therefore I cannot test all that myself.
But I am sure that you can manage that yourself if you start with a simple working example, change things step by step and check what happens.
Good Luck.
Helmut
Use ORG directive.
For example, for a function to start at location 2000H
ORG 2000H
MY_FUNC:
: YOUR CODE HERE
RET