I have a 64-bit system, but gcc is 32-bits and when I do
>./gcc -c foobar.c
it makes foobar.o which is 64-bits. OK, but how does it know to do that? Based on what environment setting does it know to produce 64-bit object, and where is that documented??
Come to think about it, it is strange that it does that, is it not?? But file utility clearly says, gcc is 32 bits and foobar.o is 64 bits. ( I moved everything to the same directory so it would not be confused. )
I also checked the 3 dynamically linked libraries that it reads: libc, libm and libz and they are also all 32 bits.
To clarify, I don't want to know, how to make it do 32 bits. I want to know, what is it looking at now that it makes it do 64. That is my question, not how to force it the other way around.
When GCC is configured three different systems can be specified:
build: - the system where GCC is going to be built (probably not
relevant to your question)
host: - the system where GCC is going to
be executed (32 bit in your case)
target: the system where binaries, produced by GCC are going to be executed (64 bit in your case)
You can see how your GCC was configured by running:
gcc -v
command (look for --{build,host,target} options.
Related
I need to use the TCC compiler to link object files generated by GCC. However, GCC in MinGW outputs object files in COFF format, and TCC only supports the ELF format. How can I make GCC generate ELF object files?
$ cat test.c
int main(void)
{
return 0;
}
$ gcc -c test.c
$ file test.o
test.o: MS Windows COFF Intel 80386 object file
$ tcc -c test.c
$ file test.o
test.o: ELF 32-bit LSB relocatable, Intel 80386, version 1 (SYSV), not stripped
However, GCC in MinGW outputs object files in COFF format
GCC can be configured to generate various outputs (including ELF) regardless of which host it runs on.
That is, a GCC running on Linux could be configured to generate COFF, and a GCC running on Windows could be configured to generate ELF32 or ELF64, for various processors (e.g. x86, or SPARC, or MIPS).
A compiler that runs on one kind of host, but generates code for a different kind, is called a cross-compiler.
TCC only supports the ELF format
This is not a meaningful statement: it could mean that you want GCC to generate ELF32 for i686 Linux, or ELF64 for SPARC Solaris, or any number of other processor/os/bit combinations.
You should figure out what target processor and operating system you want to run your final executable on, and then build (non-trivial) or download appropriate cross-compiler from Windows to that target.
file test.o
test.o: ELF 32-bit LSB relocatable, Intel 80386, version 1 (SYSV), not stripped
Ok, you want Windows to Linux/i386/ELF32 cross-compiler.
strip might help. strip accepts various object file formats for input and output type (the bfdname). strip --info for the supported formats.
strip -o outputname -O elf32-i386 objfile Doing so on a 64 bit executable, converted to 32bit control headers will lead to nothing but crash, so pick your output form carefully. Make sure you aren't changing assumed bitwidths / endians along with headers.
Not running MinGW, so, not tested, may not work for your needs, or worse, may jump and catch fire.
You want your compiler (MinGW) to generate binaries that are not of the type usable for your host system (Windows). This is called cross-compiling, and it is a somewhat involved subject -- because to create complete executables you will also need the various libraries: standard libraries, target OS libraries, third-party libraries... so it is not merely the subject of "how do I get the compiler to create ELF", but also "how do I get the whole supporting cast of ELF libs so I can link against them?".
OSDev has quite extensive documentation on the subject of setting up a cross-compiler; however, since you did not tell us what exactly your problem is, it is difficult to advise you further.
If what you want is generating Linux binaries, my advise would be to not bother with cross-compilation (which is a tricky subject -- and much better supported the other way around, i.e. targeting Windows from Linux), but rather install a Linux distribution in parallel to your Windows, and work natively with that.
It seems that gcc doesn't accept -m32 option for ARM target. I am not sure how gcc behaves on 64bit Linux, but does it automatically generate 32bit binaries if gcc is of ELF32 running on 64bit Linux?
If so, is there any workaround?
Thanks in advance.
You need to use a cross-compiler to compile for ARM from your host running either x86 or x86_64, the reason being your host and target are 2 totally independent architectures.
The cross compiler would usually be configured to output only a 32-bit or 64-bit binary for ARM (not both). Most ARM device applications make use of only 32-bit and so using an arm cross-compiler without any extra arguments would build 32-bit binaries.
Toolchains have other -m flags to specify machine type such as armv7, arm cortex a-8, etc. for further optimization. You need to look at the documentation of the ARM cross compiler.
As for getting the correct toolchain which works for your target and runs under CentOS, it is better to start at the website of the vendor of the target device.
The -m32 option provided by the x86_64 version of gcc makes gcc compile 32-bit binaries instead of 64-bit since the x86 instruction set and the x86_64 (AMD64 or Intel EMT64) are quite similar. Especially the fact that it allows executing 32-bit instructions in 64-bit mode quite easily.
I have 64 bit solaris - sparc and opteron systems. Under /usr/local/lib , I can see libiconv.so for both systems. The file command on libiconv.so gives following output:-
ELF 32-bit LSB dynamic lib 80386 Version 1, dynamically linked, not stripped, no debugging information available
How do I build 64 bit libiconv w/o disturbing existing 32 bit on both sparc and opteron systems? Reason being, I am not aware of existing version of libiconv.
This libiconv.so is not part of the OS being in the non standard /usr/local/lib. Should you want to build yourself or install from elsewhere a 64 bit version of this library, you would install it in /usr/local/lib/amd64 or /usr/local/lib/64.
However, this is probably useless in the first place as Solaris already includes the iconv library function in its standard C library so Gnu libiconv is basically redundant and unnecessary here.
I've downloaded MinGW with mingw-get-inst, and now I've noticed that it cannot compile for x64.
So is there any 32-bit binary version of the MinGW compiler that can both compile for 32-bit Windows and also for 64-bit Windows?
I don't want a 64-bit version that can generate 32-bit code, since I want the compiler to also run on 32-bit Windows, and I'm only looking for precompiled binaries here, not source files, since I've spent countless hours compiling GCC and failing, and I've given up for a while. :(
AFAIK mingw targets either 32 bit windows or 64 bit windows, but not both, so you would need two installs. And the latter is still considered beta.
For you what you want is either mingw-w64-bin_i686-mingw or mingw-w64-bin_i686-cygwin if you want to compile for windows 64. For win32, just use what you get with mingw-get-inst.
See http://sourceforge.net/apps/trac/mingw-w64/wiki/download%20filename%20structure for an explanation of file names.
I realize this is an old question. However it's linked to the many times the question has been repeated.
I have found, after lots of research that, by now, years later, both compilers are commonly installed by default when installing mingw from your repository (i.e. synaptic).
You can check and verify by running Linux's locate command:
$ locate -r "mingw32.*[cg]++$"
On my Ubuntu (13.10) install I have by default the following compilers to choose from... found by issuing the locate command.
/usr/bin/amd64-mingw32msvc-c++
/usr/bin/amd64-mingw32msvc-g++
/usr/bin/i586-mingw32msvc-c++
/usr/bin/i586-mingw32msvc-g++
/usr/bin/i686-w64-mingw32-c++
/usr/bin/i686-w64-mingw32-g++
/usr/bin/x86_64-w64-mingw32-c++
/usr/bin/x86_64-w64-mingw32-g++
Finally, the least you'd have to do on many systems is run:
$ sudo apt-get install gcc-mingw32
I hope the many links to this page can spare a lot of programmers some search time.
for you situation, you can download multilib (include lib32 and lib64) version for Mingw64:
Multilib Toolchains(Targetting Win32 and Win64)
By default it is compiled for 64bit.You can add -m32 flag to compile for 32bit program.
But sadly,no gdb provided,you ought to add it manually.
Because according to mingw-64's todo list, gcc multilib version is done,but gdb
multilib version is still in progress,you could use it maybe in the future.
Support of multilib build in configure and in gcc. Parts are already present in gcc's 4.5 version by using target triplet -w64-mingw32.
gdb -- Native support is present, but some features like multi-arch support (debugging 32-bit and 64-bit by one gdb) are still missing features.
mingw-64-todo-list
Using MacPorts i have just installed arm-elf-gcc on to my MacBook Pro. This worked flawlessly and all seems to run fine.
However, after compiling a simple hello world test program in C and C++ and trying to run either on the target board (an ARM9 based board running Debian Linux) they immediately seg fault.
I'm a bit stuck as how to go about debugging this, as the target board has limited tools available and no gdb. I have successfully built and run other code using a Linux hosted cross compiler so it should work.
Any ideas?
Following the suggestion I have built and run gdbserver, I get the following in gdb on the host:
Program received signal SIGSEGV, Segmentation fault.
0x00000000 in ?? ()
I thought it may be a problem with the standard c libs so I removed any calls and have just an empty main that return 0, it is compiled with -Wall -g hello-arm.cpp -static. As a test I compiled the same source with a Linux hosted cross compiler and it runs and exits fine. The only difference I can see is the that Linux compiled version is over twice the size and the difference in output from the file command:
arm-elf-gcc: ELF 32-bit LSB executable, ARM, version 1, statically linked, not stripped
arm-*-linux: ELF 32-bit LSB executable, ARM, version 1, statically linked, for GNU/Linux 2.4.18, not stripped
The usual method of debugging in this situation is to run gdbserver on the target board, and connect to it (via ethernet) with gdb running on a host computer.
Alternately, you could try comparing the assembly in a Mac-compiled "Hello World" program and a (working) Linux-compiled one to see what's different.
After digging around for a couple of days I am starting to understand a bit more about embedded compilers. I wasn't really sure of the difference between arm-elf-gcc installed via MacPorts and the arm-unknown-linux toolchain I had installed on my Linux box. I just came across a pdf titled "An introduction to the GNU compiler" which contains the following paragraph:
Important: Using the GNU Compiler to
create your executable is not quite
the same as using the GNU Linker,
arm-elf-ld, yourself. The reason is
that the GNU Compiler automatically
links a number of standard system
libraries into your executable. These
libraries allow your program to
interact with an operating system, to
use the standard C library functions,
to use certain language features and
operations (such as division), and so
on. If you wish to see exactly which
libraries are being linked into the
executable, you should pass the
verbose flag
-v to the compiler.
This has important implications for
embedded systems! Such systems do not
usually have an operating system.
This means that linking in the system
libraries is almost always
meaningless: if there is no operating
system, for example, then calling the
standard printf function does not make
much sense.
So when I get back to my dev machine later I will determine the libraries linked in with the Linux build and add them to the arm-elf-gcc build.
I'll update this when I have more information but I just want to document my findings in case any one else has these problems.