linking with `avr-gcc` failed

[xphoniex]

trying to compile this crate for avr target and after adding alloc and implementing a dummy allocator, I'm getting:

error: linking with `avr-gcc` failed: exit status: 1
  |
  = note: "avr-gcc" "-mmcu=atmega328p" "-Wl,--as-needed" "/arduino-lib-rs/target/avr-atmega328p/debug/deps/arduino_lib-eba03eb7ff231966.secp256k1-39ff10e3da6aca26.secp256k1.20a321c8-cgu.0.rcgu.o.rcgu.o" "-Wl,--as-needed" "-L" "/arduino-lib-rs/target/avr-atmega328p/debug/deps" "-L" "/arduino-lib-rs/target/debug/deps" "-L" "/arduino-lib-rs/target/avr-atmega328p/debug/build/secp256k1-sys-3814b449d734bc91/out" "-L" "/.rustup/toolchains/nightly-2022-07-10-x86_64-unknown-linux-gnu/lib/rustlib/avr-atmega328p/lib" "-Wl,-Bstatic" "/tmp/rustcbzOoYn/libsecp256k1_sys-3a3f6b652e34c422.rlib" "/arduino-lib-rs/target/avr-atmega328p/debug/deps/libcompiler_builtins-7aa2be695e3a21ba.rlib" "-Wl,-Bdynamic" "-lgcc" "-Wl,-znoexecstack" "-L" "/.rustup/toolchains/nightly-2022-07-10-x86_64-unknown-linux-gnu/lib/rustlib/avr-atmega328p/lib" "-o" "/arduino-lib-rs/target/avr-atmega328p/debug/deps/arduino_lib-eba03eb7ff231966.elf" "-Wl,--gc-sections"
  = note: /tmp/rustcbzOoYn/libsecp256k1_sys-3a3f6b652e34c422.rlib: error adding symbols: File format not recognized
          collect2: error: ld returned 1 exit status

I tried RUSTFLAGS="--cfg=rust_secp_no_symbol_renaming" too, doesn't work.

anyone knows why I'm getting this error? is it even possible to link this for avr without extra work/config?

[Kixunil]

It looks like you're trying to link your project with a Rust library using gcc instead of rustc.

[xphoniex]

hm... I'm following the template from Rahix/avr-hal and it works when importing other no_std crates, you can see an exmaple here.

[Kixunil]

I think it could be unimplemented in the cc crate. There's no mention of AVR in issues, PRs or code. Did you try any other C-wrapping library which uses the CC crate?

[xphoniex]

It compiles fine if I remove the alloc feature with secp256k1 crate, not sure if that counts?

[Kixunil]

Oh that's really surprising. The feature should only affect which functions are available, not how linking is performed. Could you try to compile both cases with verbose flag and compare what's different?

[xphoniex]

made a mistake, the reason it was linking without alloc feature was because no code from secp256k1 was being used.

here's the verbose output:

       Fresh core v0.0.0 (/.rustup/toolchains/nightly-2022-07-10-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core)
       Fresh unicode-ident v1.0.6
       Fresh cc v1.0.41
       Fresh rustc-std-workspace-core v1.99.0 (/.rustup/toolchains/nightly-2022-07-10-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/rustc-std-workspace-core)
       Fresh compiler_builtins v0.1.73
       Fresh proc-macro2 v1.0.51
       Fresh alloc v0.0.0 (/.rustup/toolchains/nightly-2022-07-10-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/alloc)
       Fresh quote v1.0.23
       Fresh rustversion v1.0.11
       Fresh proc-macro-hack v0.5.20+deprecated
       Fresh paste v1.0.11
       Fresh syn v1.0.107
       Fresh nb v1.0.0
       Fresh void v1.0.2
       Fresh ufmt-write v0.1.0
       Fresh vcell v0.1.3
       Fresh cfg-if v1.0.0
       Fresh bare-metal v1.0.0
       Fresh cfg-if v0.1.10
       Fresh embedded-storage v0.2.0
       Fresh secp256k1-sys v0.8.0
       Fresh panic-halt v0.2.0
       Fresh ufmt-macros v0.2.0
       Fresh nb v0.1.3
       Fresh avr-device-macros v0.5.0
       Fresh secp256k1 v0.26.0
       Fresh embedded-hal v0.2.7
       Fresh ufmt v0.1.2
       Fresh avr-device v0.5.0
       Fresh avr-hal-generic v0.1.0 (https://github.com/rahix/avr-hal?rev=4c9c44c314eb061ee20556ef10d45dea36e75ee4#4c9c44c3)
       Fresh atmega-hal v0.1.0 (https://github.com/rahix/avr-hal?rev=4c9c44c314eb061ee20556ef10d45dea36e75ee4#4c9c44c3)
       Fresh arduino-hal v0.1.0 (https://github.com/rahix/avr-hal?rev=4c9c44c314eb061ee20556ef10d45dea36e75ee4#4c9c44c3)
   Compiling arduino-lib v0.1.0 (/arduino-lib-rs)
     Running `rustc --crate-name arduino_lib --edition=2021 src/main.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --crate-type bin --emit=dep-info,link -C opt-level=s -C panic=abort -C lto -C debuginfo=2 -C debug-assertions=on -C metadata=4fc5e0f08d0e8413 -C extra-filename=-4fc5e0f08d0e8413 --out-dir /arduino-lib-rs/target/avr-atmega328p/debug/deps --target /arduino-lib-rs/avr-atmega328p.json -C incremental=/arduino-lib-rs/target/avr-atmega328p/debug/incremental -L dependency=/arduino-lib-rs/target/avr-atmega328p/debug/deps -L dependency=/arduino-lib-rs/target/debug/deps --extern 'noprelude:alloc=/arduino-lib-rs/target/avr-atmega328p/debug/deps/liballoc-6657415c07dc6074.rlib' --extern arduino_hal=/arduino-lib-rs/target/avr-atmega328p/debug/deps/libarduino_hal-ab70d292f4898b57.rlib --extern 'noprelude:compiler_builtins=/arduino-lib-rs/target/avr-atmega328p/debug/deps/libcompiler_builtins-7aa2be695e3a21ba.rlib' --extern 'noprelude:core=/arduino-lib-rs/target/avr-atmega328p/debug/deps/libcore-5992387ffdde5367.rlib' --extern panic_halt=/arduino-lib-rs/target/avr-atmega328p/debug/deps/libpanic_halt-c807d160b6ac4a90.rlib --extern secp256k1=/arduino-lib-rs/target/avr-atmega328p/debug/deps/libsecp256k1-3da03d9a855cade0.rlib -Z unstable-options -L native=/arduino-lib-rs/target/avr-atmega328p/debug/build/secp256k1-sys-71731f20ca02ee1b/out`
WARN rustc_codegen_ssa::back::link Linker does not support -no-pie command line option. Retrying without.
error: linking with `avr-gcc` failed: exit status: 1
  |
  = note: "avr-gcc" "-mmcu=atmega328p" "-Wl,--as-needed" "/arduino-lib-rs/target/avr-atmega328p/debug/deps/arduino_lib-4fc5e0f08d0e8413.secp256k1-3da03d9a855cade0.secp256k1.96b2e4ee-cgu.0.rcgu.o.rcgu.o" "-Wl,--as-needed" "-L" "/arduino-lib-rs/target/avr-atmega328p/debug/deps" "-L" "/arduino-lib-rs/target/debug/deps" "-L" "/arduino-lib-rs/target/avr-atmega328p/debug/build/secp256k1-sys-71731f20ca02ee1b/out" "-L" "/.rustup/toolchains/nightly-2022-07-10-x86_64-unknown-linux-gnu/lib/rustlib/avr-atmega328p/lib" "-Wl,-Bstatic" "/tmp/rustcDNjnWV/libsecp256k1_sys-78f272f5c76a5ef9.rlib" "/arduino-lib-rs/target/avr-atmega328p/debug/deps/libcompiler_builtins-7aa2be695e3a21ba.rlib" "-Wl,-Bdynamic" "-lgcc" "-Wl,-znoexecstack" "-L" "/.rustup/toolchains/nightly-2022-07-10-x86_64-unknown-linux-gnu/lib/rustlib/avr-atmega328p/lib" "-o" "/arduino-lib-rs/target/avr-atmega328p/debug/deps/arduino_lib-4fc5e0f08d0e8413.elf" "-Wl,--gc-sections"
  = note: /tmp/rustcDNjnWV/libsecp256k1_sys-78f272f5c76a5ef9.rlib: error adding symbols: File format not recognized
          collect2: error: ld returned 1 exit status

error: could not compile `arduino-lib` due to previous error

Caused by:
  process didn't exit successfully: `rustc --crate-name arduino_lib --edition=2021 src/main.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --crate-type bin --emit=dep-info,link -C opt-level=s -C panic=abort -C lto -C debuginfo=2 -C debug-assertions=on -C metadata=4fc5e0f08d0e8413 -C extra-filename=-4fc5e0f08d0e8413 --out-dir /arduino-lib-rs/target/avr-atmega328p/debug/deps --target /arduino-lib-rs/avr-atmega328p.json -C incremental=/arduino-lib-rs/target/avr-atmega328p/debug/incremental -L dependency=/arduino-lib-rs/target/avr-atmega328p/debug/deps -L dependency=/arduino-lib-rs/target/debug/deps --extern 'noprelude:alloc=/arduino-lib-rs/target/avr-atmega328p/debug/deps/liballoc-6657415c07dc6074.rlib' --extern arduino_hal=/arduino-lib-rs/target/avr-atmega328p/debug/deps/libarduino_hal-ab70d292f4898b57.rlib --extern 'noprelude:compiler_builtins=/arduino-lib-rs/target/avr-atmega328p/debug/deps/libcompiler_builtins-7aa2be695e3a21ba.rlib' --extern 'noprelude:core=/arduino-lib-rs/target/avr-atmega328p/debug/deps/libcore-5992387ffdde5367.rlib' --extern panic_halt=/arduino-lib-rs/target/avr-atmega328p/debug/deps/libpanic_halt-c807d160b6ac4a90.rlib --extern secp256k1=/arduino-lib-rs/target/avr-atmega328p/debug/deps/libsecp256k1-3da03d9a855cade0.rlib -Z unstable-options -L native=/arduino-lib-rs/target/avr-atmega328p/debug/build/secp256k1-sys-71731f20ca02ee1b/out` (exit status: 1)

[Kixunil]

So it looks like I'm correct in guessing AVR is not supported by cc?

[xphoniex]

I don't see cc being used, can you point me to the line? Instead it's using avr-gcc which should support avr?

[Kixunil]

I mean the crate.

[xphoniex]

if by crate you mean secp256k1, well that's basically my question.

I want to know if it supports avr and if not why, what needs to be changed?

[apoelstra]

By crate he means the cc crate, which appears not to support AVR ... or at least, has no evidence that anyone has tried to use it with AVR until now.

I'm happy to leave this open because I think libsecp-on-AVR is pretty cool...but I think the fix is going to have to happen in the cc crate and that there's not much we can do hree.

[xphoniex]

ah, I think I get it now.

my lib calls rust-secp256k1 which calls cc, that's why we're getting:

error adding symbols: File format not recognized

correct?

this file has to be changed for avr to work.

[apoelstra]

Yep, exactly. And I don't know how/if we can change that file to support AVR; the cc crate is the standard way to "call a C compiler for any platform you might support" so if it doesn't support AVR I worry that nothing will.

If it worked for you, I'd be willing to accept an ad-hoc change that did something like if cfg!(target = "avr") { /* explicitly call avr-gcc with std::process::Command or something */; return Ok(()); }. But I won't be able to make such a change, or test it. I can just verify that it won't affect non-AVR users and accept it on those grounds :P.

[xphoniex]

sounds fair, will check if I can get it to work once I find some time.

[Kixunil]

If you can, I think your time would be better spent on making a PR to the cc crate, since that'll benefit many more users. I also think AVR is cool and even have some Arduinos around but sadly, I don't have time to help you much. So I can only wish you good luck!