Building ESP32 with Cargo instead of Xargo

[Hecatron]

Hi,
I've recently been experimenting building the code using cargo instead of xargo for an ESP32, so I can use it as a basis for my own projects.
Since xargo is in maintenance mode and cargo-xbuild now recommends using vanilla cargo with the build-std feature

Thanks for all you're hard work btw on getting rust running on the esp32
What I've discovered is that this seems to work in release but not in debug mode
I think it's because the mem functions from esp32hal are conflicting with with the ones in compiler-builtins

Changes for Cargo build

First these are the changes I made to build using cargo instead of xargo

• First rename .config/config to .config/config.toml
  This isn't actually needed but seems to be the new convention
  although the old xargo doesn't pick up on .config/config.toml only cargo does that

• Next switch to the nightly toolchain, I think this gives the latest version of cargo
  even though I'm using a custom rustc / llvm build for the esp32

rustup default nightly

• Next instead of setting environmental variables like with xargo
  we can now add the custom paths to rustc / rustdoc in the .config/config.toml
• Also add build-std core mode

[build]
target = "xtensa-esp32-none-elf"
rustc = "D:\\Example\\rust-xtensa\\build\\x86_64-pc-windows-msvc\\stage2\\bin\\rustc.exe"
rustdoc = "D:\\Example\\rust-xtensa\\build\\x86_64-pc-windows-msvc\\stage2\\bin\\rustdoc.exe"

[unstable]
build-std = ["core"]

Next I added to Config.Toml the default features to enable
just so I didn't have to keep adding them to the command line, this is just for the esp32

[features]
default = ["xtensa-lx-rt/lx6", "xtensa-lx/lx6", "esp32-hal"]

Finally to build

# Set Backtrace
set export RUST_BACKTRACE=1

# To build debug - This fails
cargo build --example esp32
# To build release - This works
cargo build --example esp32 --release

Build Failure

I get the feeling this may now have been fixed

• compiler_builtins seems to be missing symbols rust-lang/wg-cargo-std-aware#53

But I think I might be running into this problem

• Remove implicit 'mem' feature for '-none' targets. rust-lang/compiler-builtins#379

Whereby the mem functions are being picked up by both esp32hal and compiler-builtins at the same time

c:/apps/xtensa-esp32-elf/bin/../lib/gcc/xtensa-esp32-elf/8.4.0/../../../../xtensa-esp32-elf/bin/ld.exe: D:\SourceCode\External\xtensa-rust-quickstart\target\xtensa-esp32-none-elf\debug\deps\libcompiler_builtins-c4239eb2059dfa6f.rlib(compiler_builtins-c4239eb2059dfa6f.compiler_builtins.98f1mwpt-cgu.7.rcgu.o): in function `memset':
  C:\Users\ric\.cargo\registry\src\github.com-1ecc6299db9ec823\compiler_builtins-0.1.35\src/mem.rs:43: multiple definition of `memset'; D:\SourceCode\External\xtensa-rust-quickstart\target\xtensa-esp32-none-elf\debug\deps\libesp32_hal-1917a2d435a3be16.rlib(esp32_hal-1917a2d435a3be16.esp32_hal.7rewnego-cgu.2.rcgu.o):C:\Users\ric\.cargo\registry\src\github.com-1ecc6299db9ec823\esp32-hal-0.2.0\src/mem.rs:205: first defined here
  collect2.exe: error: ld returned 1 exit status

I have a feeling that it's related to the mem feature within compiler-builtins
although it's odd that it passes through release.
I'm guessing that xargo / cargo-xbuild are forcing that feature to be off which isn't a standard thing you can do under cargo since features are accumulative

I also noticed the final binary was 100Kb larger in release mode when built with cargo vs xargo (in that the cargo built version was bigger)
although that might be the mem feature being enabled perhaps or the fact
it's pulling in the core / rustc-std-workspace-core libraries

Any thoughts?
I can build with xargo, it just seems that cargo is more convenient since it needs less env variables to be set
I've not been using rust that long (past week or so) so I'm currently looking into if there's a way I can fudge the mem feature to off in some way
possibly disabling all default features is something I've not tried yet

• Ability to disable individual default features rust-lang/cargo#3126

[MabezDev]

Now that rust-lang/compiler-builtins#411 is merged, we are step closer to building with just cargo 🎉 . Will need a compiler builtins release, then I will need to update the rust-xtensa fork, which I want to do anyways as we now have const generics on stable.

I also noticed the final binary was 100Kb larger in release mode when built with cargo vs xargo (in that the cargo built version was bigger)

Hmm thats odd. Are you noticing that in size of the elf file, or is that the increased size once you've converted from elf to bin? If its in the elf, it may be debug symbols from the core lib perhaps.

[MabezDev]

It's now possible, and the default to build with cargo via #44 🎉.