Assembly for little-endian xtensa?

Question

I'm trying to assemble some basic testing code for an embedded device I'm reverse-engineering, which runs little-endian xtensa threadx. From googling the only assembler that seems to support xtensa in my linux distro's repos (fedora) is GNU Assembler (xtensa-linux-gnu-as).

However when assembling code the output is always big-endian, with seemingly no way to change it to little-endian. Typical relevant GNU assembler options for other architectures (-mlittle-endian, -EL) don't seem to be supported for xtensa.

Is there some obscure way I couldn't find to make xtensa-linux-gnu-as output little endian? Or some other alternate assembler I can use instead that does?

Example assembly for xtensa-linux-gnu-as:

.int 0x12345678

Assembled output hex dump:

00000000: 1234 5678                                .4Vx

jcmvbkbc · Accepted Answer · 2025-09-25 04:41:56Z

2

GNU binutils version 2.40 or newer support dynamic xtensa core configuration. It can be built with the following project: https://github.com/jcmvbkbc/xtensa-dynconfig/tree/original using xtensa configuration overlay of your specific core or one of the predefined cores available here: https://github.com/jcmvbkbc/xtensa-toolchain-build/tree/master/overlays/original

As an example the following script builds dynconfig library for the esp32s3:

git clone https://github.com/jcmvbkbc/xtensa-dynconfig -b original
git clone https://github.com/jcmvbkbc/config-esp32s3 esp32s3
make -C xtensa-dynconfig ORIG=1 CONF_DIR=`pwd` esp32s3.so

export XTENSA_GNU_CONFIG=`pwd`/xtensa-dynconfig/esp32s3.so

If you run the assembler with the XTENSA_GNU_CONFIG environment variable set as shown above it will generate fairly generic code for little-endian xtensa.

answered Sep 25 at 4:41

jcmvbkbc

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