Building 32bit binary for ARM on 64bit CentOS - gcc

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.

Related

Cross compilation for x86-64 target on arm64 host

I'm trying to find a way to do cross-compilation for x86-64 target on an arm64 machine, the gcc version used is 4.8.5 (Old version. I know...).
My host is an Apple M1 machine, and the program can be built only on Linux.
I tried creating a docker container that emulates x86-64 using QEMU - but its terribly slow.
I'm now trying to use a linux container (or a vm) and looking for a arm64 to x86 cross compiler, I have used arm64 to x86-64 compilers in the past, but can't find the reverse one.
Thanks

Compile and run a 32bit binary on Armv8 (aarch64) running 64bit linux

I'am trying to compile and run a 32 bit binary on a Cortex-A72 Armv8 using gcc compiler but i am not able to do it. I followed this prior thread Having trouble compiling 32-bit binary on 64-bit linux armv8 machine and i am realized too that the -m32 flag is not supported on ARMv8 linux machines.
Looking at https://gcc.gnu.org/onlinedocs/gcc/AArch64-Options.html i didn’t find anything interesting.
In according to https://linux.die.net/man/1/arm-linux-gnu-gcc the AArch64 gcc options are:
-mbig-endian -mlittle-endian -mgeneral-regs-only -mcmodel=tiny -mcmodel=small -mcmodel=large -mstrict-align -momit-leaf-frame-pointer -mno-omit-leaf-frame-pointer -mtls-dialect=desc -mtls-dialect=traditional -march=name -mcpu=name -mtune=name
So my question is: is it possible to compile and run a 32-bit binary on a 64-bit linux Armv8 machine ? and is so, how ?
Thank you.
EDIT: this https://jensd.be/1126/linux/cross-compiling-for-arm-or-aarch64-on-debian-or-ubuntu worked for me

You can download the AArch32 target with hard float (arm-none-linux-gnueabihf) toolchain from the Cortex-A toolchain Arm site.
The archive file name is gcc-arm-10.2-2020.11-aarch64-arm-none-linux-gnueabihf.tar.xz, in the AArch64 Linux hosted cross compilers section.
You may need to install additional packages on your Aarch64 system - search for How to run 32-bit (armhf) binaries on 64-bit (arm64) and your Linux distribution name.

Compiling 32-bit OS X binaries on a 64-bit environment

What is involved in compiling 32-bit Intel OS X binaries on a 64-bit command-line environment? Is it as simple as adding a -m32 flag? I'm not using Xcode, but could use it to install libraries that gcc could use, if needed. Thanks for your advice.

If you're compiling on a Macintosh computer using Apple's implementation of GCC, one of the extra options you can pass along is the "-arch" parameter.
The man page says this:
-arch arch
Compile for the specified target architecture arch.
The allowable values are i386, x86_64, ppc and ppc64.
Multiple options work, and direct the compiler to produce "universal"
binaries including object code for each architecture specified with -arch.
This option only works if assembler and libraries are available
for each architecture specified. (APPLE ONLY)

How to specify win32 or Windows 64 target with cross compiler i686-w64-mingw32-gcc

I have recently downloaded the mingw-w64 package under Fedora Linux in order to be able to cross compile targetting both win32 and "Windows 64". But I fail to understand how to specify what target I want to use. What flags do I need to supply to gcc and to the linker in order to choose my target architecture?

W32 and W64 are two different architectures, so you distinguish by compiler name. The debian mingw-w64 calls them i686-w64-mingw32-gcc for Win32 and x86_64-w64-mingw32-gcc for Win64.

Mac OSX 10.6 compiler: a puzzling experience with 32 vs 64 bit

I have trouble understanding the gcc compiler provided by OSX 10.6 snow leopard, mainly because of my lack of experience with 64 bits environments.
$ cat >foo.c
main() {}
$ gcc foo.c -o foo
$ file foo
foo: Mach-O 64-bit executable x86_64
$ lipo -detailed_info foo
input file foo is not a fat file
Non-fat file: foo is architecture: x86_64
However, my architecture is seen as an intel i386 type (I have one of the latest Intel Core2 duo MacBook)
$ arch
i386
and the compiler targets i686-apple-darwin10
$ gcc --version
i686-apple-darwin10-gcc-4.2.1 (GCC) 4.2.1 (Apple Inc. build 5646)
Of course, if I compile 32 bits I get a 32 bit executable.
$ gcc -m32 foo.c -o foo
$ file foo
foo: Mach-O executable i386
but I don't get the big picture. The default setup for the compiler is to produce x86_64 executables, even if I have arch saying I have a 32 bit machine (why? Core2 is 64); even if (I guess) I am running a 32 bit kernel; even if I have a compiler targeting the i686-apple-darwin platform. Why? How can they run ? Should I compile 64 or 32 ?
This question is due to my attempt to compile gcc 4.2.3 on the mac, but I am having a bunch of issues with gmp, mpfr and libiberty getting (in some cases) compiled for x86_64. Should I compile everything x86_64 ? If so, what's the target (not i686-apple-darwin10 I guess)?
Thanks for the help

The default compiler on Snow Leopard is gcc4.2, and its default architecture is x86_64. The typical way to build Mac software is to build multiple architectures in separate passes, then use lipo to combine the results. (lipo only compiles single-arch files into a multiple-arch file, or strips archs out of a multi-arch file. It has no utility on single-arch files, as you discovered.)
The bitness of the compiler has nothing to do with anything. You can build 32-bit binaries with a 64-bit compiler, and vice versa. (What you think is the "target" of the compiler is actually its executable, which is different.)
The bitness of the kernel has nothing to do with anything. You can build and run 64-bit binaries when booted on a 32-bit kernel, and vice versa.
What matters is when you link, whether you have the appropriate architectures for linking. You can't link 32-bit builds against 64-bit binaries or vice versa. So the important thing is to see what the architectures of your link libraries are, make sure they're coherent, then build your binary of the same architecture so you can link against the libraries you have.

i686-apple-darwin10.0.0 contains an x86_64 folder which is not understood by most versions of autotools. In other words, I'd say that the gcc compiler is unfortunately nothing short of a joke on Snow Leopard. Why you would bundle 32-bit and 64-bit libraries into i686-apple-darwin10.0.0 is beyond me.
$ ls /usr/lib/gcc
i686-apple-darwin10 powerpc-apple-darwin10
You need to change all your autotools configure files to handle looking in *86-darwin directories and then looking for 64-bit libraries I'd imagine.
As with your system, my mac mini says its i386 even though its obviously using a 64-bit platform, again another mistake since its distributed with 64-bit hardware.
$arch
i386

Apple toolchains support multiple architectures. If you want to create a fat binary that contains x86 and x86_64 code, then you have to pass the parameters -arch i386 -arch x86_64 to gcc. The compiler will compile your code twice for both platforms in one go.
Adding -arch i386 -arch x86_64 to CFLAGS may allow you to compile gmp, mpfr, and whatnot for multiple archs in one go. Building libusb that way worked for me.

This answer is wrong, but see comments below
The real question is... how did you get a 32-bit version of OSX? I wasn't aware that Snow Leopard had a 32-bit version, as all of Apple's Intel chips are Core 2 or Xeon, which support the x86_64 architecture.
Oh, and Snow Leopard only works on Intel chips.
Edit: Apparently Snow Leopard starts in 32-bit mode.

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