Hi,
Thanks for the info.
What I understood from this is that emulation
is something which ‘ld’ uses to know about target platform and the
format of the final linked file to be created, like .out or .so or elf format.
Can you tell me why we are using these target and format specific options at
linking time, rather than using them at compile time. If the compiler has made
the object files according to some specific format, how can linker change that
format?
As far as I know compiler creates an
object file (binary file) for each source file. At this stage all the function
calls are resolved if the function’s definition is present in same source
file, so it’s a source file specific operation and it need not to know anything
about other source files, that is why when we make a single file kernel module we
just give the ‘–c’ (compile) option and not the linking (-o)
option. If there are any function calls whose function definitions are present
in some other source file, that function call is not resolved at this time,
this thing is done by the linker in next stage.
Now at linker stage all unresolved
function calls, either related to library functions or used defined function (whose
definitions are present in other source files) are resolved. Linker is not at
all concerned with the format of final file, I think the compiler should be
concerned with this.
In case I am wrong somewhere please
rectify it.
Regards,
GD
From: matrix reloaded
[mailto:matrix_reloaded18@rediffmail.com]
Sent: Wednesday, June 23, 2004
11:24 AM
To: Dhiman,
Gaurav
Cc: Kernel Newbies
Subject: Re: RE: How to link the
module ?
Hi,
here are some details about emulation (-m flag) :-
A linker emulation is a "personality" of the linker, which gives the
linker default
values for the other aspects of the target system. In particular, it consists
of
1. the linker script
2. the target
3. several "hook" functions that are run at certain stages of the
linking process to
do special things that some targets require
The command to list valid linker emulation values is "prefix-ld -V".
In this case
command would be :-
$ ld -V
Sample values: "elf_i386", "i386linux",
"coff_i186", "coff_m68k".
Ways to specify:
command line option: "-m"
environment variable LDEMULATION
compiled-in DEFAULT_EMULATION from Makefile, which comes from EMUL in
config/target.mt
Basically ld looks for some emulation settings and If the -m
option is not used,
the emulation is taken from the "LDEMULATION" environment variable,
if that is
defined. Otherwise, the default emulation depends upon how the
linker was
configured.
Regards,
Sumit Sharma.
On Tue, 22 Jun 2004 Dhiman,Gaurav wrote :
>
>Thanks to all!!
>Able to get it linked.
>
>Changed the linking command to
>
>ld -m elf_i386 -r -o driver.o main.o. pipe.o fifo.o msg_q.o
>
>Nobody told me about the use of -m option and elf_i386 value given to
>liker.
>Can someone please make clear, what is the use of "-m elf_i386"
in
>linking command. On man pages of ld its mentioned that -m is used to
>specify different emulation, what does that mean?
>
>Regards,
>GD.
>
>
>-----Original Message-----
> From: mohanlal jangir [mailto:mohanlal@samsung.com]
>Sent: Tuesday, June 22, 2004 2:13 PM
>To: Dhiman, Gaurav; Vishwas
Raman
>Cc: Kernel Newbies
>Subject: Re: How to link the module ?
>
>You have to give output file name after -o option.
>Change ld $(LFLAGS) main.o pipe.o fifo.o msg_q.o
>to ld $(LFLAGS) $@ main.o pipe.o fifo.o msg_q.o
>
>Regards
>Mohanlal
>
>----- Original Message -----
> From: "Dhiman, Gaurav"
<Gaurav.Dhiman@ca.com>
>To: "Vishwas Raman" <vishwas@eternal-systems.com>
>Cc: "Kernel Newbies" <kernelnewbies@nl.linux.org>
>Sent: Tuesday, June 22, 2004 11:37 AM
>Subject: RE: How to link the module ?
>
>
>
>Hi,
>
>I tried what you suggested, but when I run that command it gives a lot
>of linking errors saying multiple definations of functions.
>
>I looked for the same on net and found one simple makefile containing
>the following command for linking:
>
>ld -m elf_i386 -r -o pipe.c fifo.c msg_q.c main.c
>
>When I include this linking command in my Makefile, it does not give any
>error and creates the corresponding .o file for each .c file but does
>not create the single relocatable object file through which I can load
>or unload the module. I do not get any error with following makefile,
>but at the same time it does not link the .o file to make final module.
>Please let me know what the problem is
>
>Also please explain me about -m option of 'ld', whats the use of this
>option ?
>
>I am pasting below my Makefile for your reference
>
>******************************************
>Makefile - Starts
>******************************************
>
>KERNELDIR = /usr/src/linux-2.4
>
>CC = gcc
>
>include $(KERNELDIR)/include/linux/config.h
>
>CFLAGS = -I$(KERNELDIR)/include -D__KERNEL__ -DMODULE \
> -O -Wall -c
>
>LFLAGS = -m elf_i386 -r -o
>
>ifdef CONFIG_SMP
>CFLAGS += -DSMP
>endif
>
>all: driver.o
>
>driver.o: main.o pipe.o fifo.o msg_q.o
>ld $(LFLAGS) main.o pipe.o fifo.o msg_q.o
>
>main.o: main.c
>$(CC) $(CFLAGS) main.c
>
>fifo.o: fifo.c
>$(CC) $(CFLAGS) fifo.c
>
>pipe.o: pipe.c
>$(CC) $(CFLAGS) pipe.c
>
>msg_q.o: msg_q.c
>$(CC) $(CFLAGS) msg_q.c
>
>#all: main.o pipe.o fifo.o msg_q.o
># $(CC) $(CFLAGS) main.c pipe.c fifo.c msg_q.c
>
>clean:
>rm -f *.o *~ core
>
>******************************************
>Makefile - Ends
>******************************************
>
>Regards,
>GD.
>
>
>
>-----Original Message-----
> From: kernelnewbies-bounce@nl.linux.org
>[mailto:kernelnewbies-bounce@nl.linux.org] On Behalf Of Vishwas Raman
>Sent: Monday, June 21, 2004 10:02 PM
>To: Gaurav Dhiman
>Cc: Kernel Newbies
>Subject: Re: How to link the module ?
>
>ld -r *.o -o complete_module.o
>
>and then do an insmod on complete_module.o to insert the module in the
>running kernel.
>
>this should work.
>
>-Vishwas.
>
>
>On Mon, 2004-06-21 at 07:43, Gaurav Dhiman wrote:
> > Hi,
> >
> > I have made the multi source file module and compiled it sucssufully
> > with following comand:
> >
> > gcc - c main.c pipe.c fifo.c msg_q.c
> >
> > Now I have the corresponding .o file with me. Can someone tell me how
> > can I link it to each other to form one file of module. How can we
> > resolve the internal reference (reference to our own variable and
> > functions) without getting any errors or warninng for kernel symbols.
> > I know kernel symbols are resolved at load time by 'insmod'.
> > Please let me know how to resolve the internal symbols and get one
> > file for module which we can load using 'insmod'. Please let me know
> > the command.
> >
> > Regards,
> > Gaurav.
> >
> >
> >
> >
______________________________________________________________________
> > Do you Yahoo!?
> > New and Improved Yahoo! Mail - 100MB free storage!
>
>
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>
>
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>
>
>
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