Question 38530 in Ubuntu Question posted in
The official Ubuntu documentation can be found here.

Assembling ARM instructions on x86_64 – Ubuntu

I have a file, foo.S, which contains ARM thumb instructions, on an Ubuntu 22.04 x86_64 machine. Is it possible to convert this into an ARM object file using as from binutils or do I need to create a cross-compiler toolchain? I tried

$ as -mthumb foo.S -o foo.o

However, I got

as: unrecognized option '-mthumb'

even though that’s one of the options listed in man as.

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2

Answers


  1. 0

    A minimal and deterministic procedure for assembling a .S file targeting the T32 instruction set on an Ubuntu 22.04 x86_64 machine could be to install the latest Arm toolchain for arm-none-eabi

    if you don’t have wget installed, just execute:
    sudo apt-get install wget, or download arm-gnu-toolchain-11.3.rel1-x86_64-arm-none-eabi.tar.xz using a WEB browser into you home directory.

    Once done:

    cd ${HOME}
# Skip the wget command hereafter if arm-gnu-toolchain-11.3.rel1-x86_64-arm-none-eabi.tar.xz was already downloaded into your home directory.
wget "https://developer.arm.com/-/media/Files/downloads/gnu/11.3.rel1/binrel/arm-gnu-toolchain-11.3.rel1-x86_64-arm-none-eabi.tar.xz?rev=95edb5e17b9d43f28c74ce824f9c6f10&hash=176C4D884DBABB657ADC2AC886C8C095409547C4" -O arm-gnu-toolchain-11.3.rel1-x86_64-arm-none-eabi.tar.xz
tar Jxf arm-gnu-toolchain-11.3.rel1-x86_64-arm-none-eabi.tar.xz

    You can now assemble your program using the command:

    ${HOME}/arm-gnu-toolchain-11.3.rel1-x86_64-arm-none-eabi/bin/arm-none-eabi-gcc -c -mthumb foo.S -o foo.o

    Please note that a file with the .S extension usually requires to be processed using cpp, the C preprocessor – this is why the command is using arm-none-eabi-gcc, and not arm-none-eabi-as.

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  2. 0

    run

    sudo sh -c 'apt update;apt install binutils-arm-none-eabi;'

    then the code can be compiled with

    arm-none-eabi-as -mthumb foo.S -o foo.o

    example:

    $ echo nop > foo.S 
$ arm-none-eabi-as -mthumb foo.S -o foo.o
$ echo $?
0
$ file foo.o
foo.o: ELF 32-bit LSB relocatable, ARM, EABI5 version 1 (SYSV), not stripped
    • i gathered this from @Nate Eldredge and @old_timer in the comments.
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