Cross-endian linking error when building littlefs2-sys for xtensa-esp32s3-none-elf

[anilperi]

I am encountering a linker error when building my no_std project for the xtensa-esp32s3-none-elf target using littlefs2. The error indicates a cross-endian linking issue with the littlefs2-sys crate's object files.

The specific error message is:

/Users/anilp/.rustup/toolchains/esp/xtensa-esp-elf/esp-14.2.0_20240906/xtensa-esp-elf/bin/../lib/gcc/xtensa-esp-elf/14.2.0/../../../../xtensa-esp-elf/bin/ld: cross-endian linking for /var/folders/.../liblittlefs2_sys-...rlib(9276db2ed6ff6dcb-lfs.o) not supported
collect2: error: ld returned 1 exit status

(Similar errors occur for lfs_util.o and string.o from littlefs2_sys.rlib)

Steps Taken & Analysis:

Verified toolchain installation and PATH by running which xtensa-esp32-elf-gcc. The compiler executable was found at /Users/anilp/.rustup/toolchains/esp/xtensa-esp-elf/esp-14.2.0_20240906/xtensa-esp-elf/bin/xtensa-esp32-elf-gcc.
Attempted build after sourcing the ESP environment script (. $HOME/export-esp.sh). The error persisted.
Attempted build after explicitly setting the CC environment variable to the path of xtensa-esp32-elf-gcc (export CC="...") and running cargo clean. The error still persisted.
Analyzed the verbose build output (cargo build -vv --release --target xtensa-esp32s3-none-elf) with the CC variable set.

Finding from Verbose Output:

The verbose output shows that cc-rs, when compiling the LittleFS C code (lfs.c, lfs_util.c, string.c) within littlefs2-sys, is indeed using the correct compiler (xtensa-esp32-elf-gcc as specified by CC). However, the executed C compilation command lacks explicit endianness flags (like -mlittle-endian) or possibly sufficient architecture flags (-march=, -mabi=) to ensure little-endian compilation for the Xtensa target.

This seems to result in the compiler producing object files with big-endian target data for these generic C files, which are incompatible with the little-endian ESP32-S3 during the final linking step.

Expected Behavior:

The build should complete successfully, linking code compiled for the little-endian xtensa-esp32s3-none-elf target.

Actual Behavior:

The build fails at the linking stage due to a cross-endian mismatch originating from the littlefs2-sys object files.

Environment:

OS: macOS
Target: xtensa-esp32s3-none-elf
Toolchain: esp-14.2.0_20240906 
Rust version: 1.86
littlefs2 version: 0.6.1
littlefs2-sys version: 0.3.1 
cc-rs version: 1.2.22

[paulhampson]

tl;dr as a workaround try adding CROSS_COMPILE="xtensa-esp32s3-elf" under [env] in your project .cargo/config.toml file.

I had a similar issue to you building under linux, but the error was that it didn't like the format of the .rlib file. When looking at the .a file output I could see that littlefs2-sys was being built using the native target rather than cross compiling. I did a lot of experimentation with patching littlefs2-sys, with minimal success until I found the CROSS_COMPILE environment variable. It seems enough to have that at the top level.

Here is the full error I had (to help anyone searching with the same issue):

error: linking with `xtensa-esp32s3-elf-gcc` failed: exit status: 1
  |
  = note:  "xtensa-esp32s3-elf-gcc" "/tmp/rustcxasugG/symbols.o" "<1 object files omitted>" "-Wl,--as-needed" "-Wl,-Bstatic" "/tmp/rustcxasugG/{liblittlefs2_sys-c74b0ceb20bf957d.rlib}.rlib" "/home/paul/projects/led-emote-board/target/xtensa-esp32s3-none-elf/release/deps/{libcompiler_builtins-df17f819c10f9067.rlib}.rlib" "-Wl,-Bdynamic" "-lbtbb" "-lbtdm_app" "-lcoexist" "-lcore" "-lespnow" "-lmesh" "-lnet80211" "-lphy" "-lpp" "-lsmartconfig" "-lwapi" "-lwpa_supplicant" "-lprintf" "-Wl,--eh-frame-hdr" "-Wl,-z,noexecstack" "-L" "/home/paul/projects/led-emote-board/target/xtensa-esp32s3-none-elf/release/build/esp-hal-022b44d3d62c3c98/out" "-L" "/home/paul/projects/led-emote-board/target/xtensa-esp32s3-none-elf/release/build/esp32s3-fe785c4e84466988/out" "-L" "/home/paul/projects/led-emote-board/target/xtensa-esp32s3-none-elf/release/build/xtensa-lx-rt-a69047dd32da8e4d/out" "-L" "/home/paul/projects/led-emote-board/target/xtensa-esp32s3-none-elf/release/build/esp-wifi-sys-c6d9446844883ff6/out" "-L" "/home/paul/projects/led-emote-board/target/xtensa-esp32s3-none-elf/release/build/littlefs2-sys-bfb670b3445141d8/out" "-o" "/home/paul/projects/led-emote-board/target/xtensa-esp32s3-none-elf/release/deps/led_emote_board-646852de406a8a16" "-Wl,--gc-sections" "-no-pie" "-Wl,-O1" "-nodefaultlibs" "-nostartfiles" "-Wl,--error-handling-script=/home/paul/projects/led-emote-board/target/release/build/led-emote-board-fae366629d9026e8/build-script-build" "-Tlinkall.x"
  = note: some arguments are omitted. use `--verbose` to show all linker arguments
  = note: /home/paul/.rustup/toolchains/esp/xtensa-esp-elf/esp-14.2.0_20240906/xtensa-esp-elf/bin/../lib/gcc/xtensa-esp-elf/14.2.0/../../../../xtensa-esp-elf/bin/ld: /tmp/rustcxasugG/liblittlefs2_sys-c74b0ceb20bf957d.rlib: error adding symbols: file format not recognized
          collect2: error: ld returned 1 exit status

[anilperi]

So, I tried the CROSS_COMPILE and CC env variables and it still messed up for me. However, there was a problem with the board I was using. Will check and try this (i ended up switching to a different way of handling the fs on my own).

[bouttier]

Work for me with these:

[env]
CC = "xtensa-esp32s3-elf-cc"
AR = "xtensa-esp32s3-elf-ar"
CFLAGS = "-mlongcalls"