Hi,

I'm cross compiling a mixed project for embedded targets (arm cortex-m4 and cortex-m33). Before I was using arm-none-eabi-gcc to compile C code and link, but to take advantage of LTO I would like to use clang to compile the C code and rustc to link.

The issue I run into is that arm-none-eabi-gcc knows where sysroot is so I don't have to provide that to bindgen and cc whereas clang doesn't.

What I prefer to do in -sys crates I own is calling out to arm-none-eabi-gcc to find the sysroot and then set it in the calls to cc/bindgen:

$ arm-none-eabi-gcc -print-sysroot
/usr/local/bin/../arm-none-eabi

The most promising solution I found that works in case others maintain them is a global override in .cargo/config.toml:

CFLAGS_thumbv8m.main-none-eabihf = "--sysroot=<HARD CODED SYSROOT>"

However setting variables in .cargo/config.toml cannot be done with runtime detected values, so all contributors need to setup this manually.

Is the best solution to have a ./bootstrap.sh script that generates such a config file or are there any better solutions? It is kind of inconvenient to have a script to run before cargo works.

Regards

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