HELP! With cygwin

[t0xic]

Hey everyone,

I been using djgpp to link/build my kernel, but I recently decided to switch over to cygwin. I get to it compile but it wants to link with a __main and _alloca. I know there is a switch to turn this off, but for the life of me I can't remember it. Also, linking with the cygwin ld tells me I can't link a.out files, and my kernel is now 20kb bigger, and I haven't added any code. <what a run on sentence>. I would appreciate any help

thanks

-t0xic

[Combuster]

Sounds like a FAQ question to me:

Creating a dedicated (cross-) compiler for your OS development work can save you many headaches. If...

* ...your system compiler drags in references to alloca() or other OS-dependent things,

( GCC Cross-Compiler )

as for the switch, my first guess would be reading the manpages

[frank]

The switches I use are

Code: Select all

-fno-builtin -nostdlib -ffreestanding

for my c files and

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-fno-builtin -nostdlib -fno-exceptions -fno-rtti

for my c++ files.

EDIT: You will really want to build a cross compiler, so that should be the first thing that you do. Unless you like PE files.

[AJ]

Hi,

I got djgpp working fine with the switches frank has mentioned, although I have now switched to Cygwin and a cross compiler. I would definitely recommend the latter.

Cheers,
Adam

[t0xic]

I use those switches too. Two questions...

- Why can't I use --no-leading-underscores?
- What did you guys use as your target machine for yuor cross compiler. When ever I try i386-pc-none or i486-linux, the makefile freaks out. If I am not trying to use elf, what exe format should I use, and how do I put it in the switch? ?i386-coff?

Any help would be appreciated.

Thanks
--t0xic

[Brynet-Inc]

Well, For one isn't it -fno-leading-underscores ?

BTW The target for ELF is clearly defined in the Wiki article GCC Cross-Compiler.

Most people use the target i486-elf or i586-elf.. But I'm guessing i386/i686 are valid as well.

[t0xic]

I meant I don't want to use elf. I'm not really sure which format I'm using lol. I've been using coff I think, as thats the default format for djgpp. I had tried -fno-leading-underscores but my cygwin is obviously screwed up.

--t0xic

[frank]

Well I do believe that cygwin defaults to no leading underscores. As for the target i686-pc-elf or i586-pc-elf is usually the one people use. Objdump says it supports

elf32-i386 coff-i386 elf32-little elf32-big srec symbolsrec tekhex binary ihex

However I think that i586-pc-msdosdjgpp is also a valid target. I can't tell you what it supports though.

[jnc100]

I meant I don't want to use elf. I'm not really sure which format I'm using lol.

I think djgpp uses coff (Microsoft style) as the object file for output from gcc/gas, and pe as the executable format that ld produces. Typically, to specify an executable format, you pass the --oformat TARGET option to ld, where TARGET is one of the targets produced by the output to ld --help.

In particular, my Cygwin ld produces:

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ld: supported targets: pe-i386 pei-i386 elf32-i386 elf32-little elf32-big srec symbolsrec tekhex binary ihex
ld: supported emulations: i386pe

although you actually can't use some of them like the elf ones from Cygwin (it expects PE output, as evidenced by the supported emulations list).

On the other hand, a cross compiled binutils will give:

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i586-elf-ld: supported targets: elf32-i386 coff-i386 elf32-little elf32-big srec symbolsrec tekhex binary ihex
i586-elf-ld: supported emulations: elf_i386

which can produce elf executables.

The 'target' which people are discussing here, like 'i586-elf' etc is actually a machine name for the target that you want your code to run on, and is passed to gcc through use of the '-b <machine>' options. All this does is run the particular version of gcc that you have requested, e.g. running 'gcc -b i586-elf' will actually just pass all your options on to i586-elf-gcc. Now each particular version of gcc you have installed will have default values for certain options, e.g. the default executable version for i586-elf is elf. Its default architecture is to generate x86 code for an i586 or above, and it doesn't add any os specific code (like i586-linux-elf would).

I would suggest you cross compile a new version of gcc and binutils under cygwin, by following the instructions in GCC_Cross-Compiler.

Regards,
John.

[t0xic]

Thanks everyone;

Ok, I got i586-elf to work, and I'm in the process of compiling the binutils, but when I try to make ld, make tells me that it has already configures ./ld, even though I delete the folder. IS this a common bug or am I doing something wrong?

Thanks

--t0xic

[frank]

Well does it complete the build process and that is just some useless little info message or does it appear to fail after telling you that?

[t0xic]

@frank

Make stops what it's doing and gives me the fail on error message

--t0xic

[frank]

First off are you following the wiki instructions and are building in a separate directory? If you are try deleting everything in build-binutils and running configure and make again.

Also when you first installed cygwin did you pick the Unix/binary option for file mode? If you picked text mode then that could be a problem.

Finally do you have a the necessary packages for building binutils. I can't remember all of them but I know you need flex and bison.

[t0xic]

I believe I found the problem. I was reading the error too literally (or maybe not enough). Make told me to run make distclean in the source directory, not the build-binutils/ld directory. Make is running fine now, hopefully no more errors =)

Thanks

--t0xic