Xtensa support

[Matheus Catarino]

On Sunday, 14 April 2024 at 07:25:07 UTC, Witold Baryluk wrote:
> On Friday, 12 April 2024 at 23:16:30 UTC, Matheus Catarino 
> wrote:
>> I've recently seen support for different target architectures 
>> on https://explore.dgnu.org .
>> What is the status of Xtensa and xtensa-gnu support? Does it 
>> support both xtensa ABIs (call0 and windowed)?
>>
>> Currently there is a need to fork espressif/LLVM when using 
>> ldc2. Is there a need to fork espressif crosstool-ng?
>
> It works. I successfully run some code with it with gdc few 
> years ago. But it is quite a work to map either reimplement all 
> the APIs in D from scratch, but it can be done as everything is 
> reasonably well documented. I only had some basic stuff like 
> GPIO, very little of timers and uart. So no networking 
> (possibly, but I had other things to do) or other stuff.
>
>
> As of xtensa ABIs I have no idea. I didn't use espressif 
> libraries. Should be possible tho.

Espressif/LLVM have xtensa-ABI (windowed) partial support, but 
GCC [upstream and fork] have both xtensa-ABI (call0 & windowed)

     ```bash
     ./gcc/esp32s3-gdc/bin/xtensa-esp32s3-elf-gdc --help=target
     The following options are target specific:
       -mabi=call0                 Use call0 ABI.
       -mabi=windowed              Use windowed registers ABI.
       -malways-memw               Always emit a MEMW before a 
load and after a store operation. Used to debug
                                   memory coherency issues.
       -mauto-litpools             Relax literals in assembler and 
place them automatically in the text section.
       -mconst16                   Use CONST16 instruction to load 
constants.
       -mdisable-hardware-atomics  Call built-in functions for 
atomic operations instead of using hardware atomic
                                   instructions. This option can 
be used if atomic operations on some memory
                                   regions need to be emulated in 
software.
       -mdynconfig=                Directory or path to dynconfig 
library.
       -mextra-l32r-costs=         Set extra memory access cost 
for L32R instruction, in clock-cycle units.
       -mfix-esp32-psram-cache-issue Work around a PSRAM cache 
issue in the ESP32 ECO1 chips.
       -mfix-esp32-psram-cache-strategy= Specify a psram cache fix 
strategy.
       -mforce-no-pic              Disable position-independent 
code (PIC) for use in OS kernel code.
       -mfused-madd                Same as -ffp-contract=fast (or, 
in negated form, -ffp-contract=off).  Uses of
                                   this option are diagnosed.
       -mlongcalls                 Use indirect CALLXn 
instructions for large programs.
       -mlra                       Use LRA instead of reload 
(transitional).
       -mno-serialize-volatile     Do not serialize volatile 
memory references with MEMW instructions.
       -mtarget-align              Automatically align branch 
targets to reduce branch penalties.
       -mtext-section-literals     Intersperse literal pools with 
code in the text section.

       Psram cache fix strategies (for use with 
-mfix-esp32-psram-cache-strategy= option):
         dupldst memw nops
     ```

src: https://github.com/espressif/gcc
src: https://github.com/espressif/crosstool-ng

- **Note:** replace `--enable-languages=c,c++` to 
`--enable-languages=c,d` or add `d` after `c++`.

```bash
$> 
/root/.espressif/tools/xtensa-esp-elf/esp-13.2.0_20230928/xtensa-esp-elf/bin/xtensa-esp-elf-gcc -v
Using built-in specs.
COLLECT_GCC=/root/.espressif/tools/xtensa-esp-elf/esp-13.2.0_20230928/xtensa-esp-elf/bin/xtensa-esp-elf-gcc
COLLECT_LTO_WRAPPER=/root/.espressif/tools/xtensa-esp-elf/esp-13.2.0_20230928/xtensa-esp-elf/bin/../libexec/gcc/xtensa-esp-elf/13.2.0/lto-wrapper
Target: xtensa-esp-elf
Configured with: 
/builds/idf/crosstool-NG/.build/xtensa-esp-elf/src/gcc/configure 
--build=x86_64-build_pc-linux-gnu 
--host=x86_64-build_pc-linux-gnu --target=xtensa-esp-elf 
--prefix=/builds/idf/crosstool-NG/builds/xtensa-esp-elf 
--exec_prefix=/builds/idf/crosstool-NG/builds/xtensa-esp-elf 
--with-local-prefix=/builds/idf/crosstool-NG/builds/xtensa-esp-elf/xtensa-esp-elf --with-headers=/builds/idf/crosstool-NG/builds/xtensa-esp-elf/xtensa-esp-elf/include --with-newlib --enable-threads=no --disable-shared --with-pkgversion='crosstool-NG esp-13.2.0_20230928' --disable-__cxa_atexit --enable-cxx-flags=-ffunction-sections --disable-libgomp --disable-libmudflap --disable-libmpx --disable-libssp --disable-libquadmath --disable-libquadmath-support --disable-libstdcxx-verbose --with-gmp=/builds/idf/crosstool-NG/.build/xtensa-esp-elf/buildtools --with-mpfr=/builds/idf/crosstool-NG/.build/xtensa-esp-elf/buildtools --with-mpc=/builds/idf/crosstool-NG/.build/xtensa-esp-elf/buildtools --with-isl=/builds/idf/crosstool-NG/.build/xtensa-esp-elf/buildtools --enable-lto --enable-target-optspace --without-long-double-128 --disable-nls --enable-multiarch --enable-languages=c,c++ --disable-libstdcxx-verbose --enable-threads=posix --enable-gcov-custom-rtio --enable-libstdcxx-time=yes
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 13.2.0 (crosstool-NG esp-13.2.0_20230928)
```

## Result

```bash
./gcc/esp32s3-gdc/bin/xtensa-esp32s3-elf-gdc -v
Using built-in specs.
COLLECT_GCC=./gcc/esp32s3-gdc/bin/xtensa-esp32s3-elf-gdc
COLLECT_LTO_WRAPPER=/home/kassane/gcc/esp32s3-gdc/bin/../libexec/gcc/xtensa-esp32s3-elf/13.2.0/lto-wrapper
Target: xtensa-esp32s3-elf
Configured with: ./configure --target=xtensa-esp32s3-elf 
--enable-languages=c,d,lto
Thread model: single
Supported LTO compression algorithms: zlib zstd
gcc version 13.2.0 (GCC)
```