73 lines
2.9 KiB
Markdown
73 lines
2.9 KiB
Markdown
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# Tips
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The following shows how to do different random small things we encountered and thought could
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be useful.
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### How to send arguments to the GCC linker
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```
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CG_RUSTFLAGS="-Clink-args=-save-temps -v" ../y.sh cargo build
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```
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### How to see the personality functions in the asm dump
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```
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CG_RUSTFLAGS="-Clink-arg=-save-temps -v -Clink-arg=-dA" ../y.sh cargo build
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```
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### How to see the LLVM IR for a sysroot crate
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```
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cargo build -v --target x86_64-unknown-linux-gnu -Zbuild-std
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# Take the command from the output and add --emit=llvm-ir
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```
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### To prevent the linker from unmangling symbols
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Run with:
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```
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COLLECT_NO_DEMANGLE=1
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```
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### How to use a custom-build rustc
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* Build the stage2 compiler (`rustup toolchain link debug-current build/x86_64-unknown-linux-gnu/stage2`).
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* Clean and rebuild the codegen with `debug-current` in the file `rust-toolchain`.
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### How to use [mem-trace](https://github.com/antoyo/mem-trace)
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`rustc` needs to be built without `jemalloc` so that `mem-trace` can overload `malloc` since `jemalloc` is linked statically, so a `LD_PRELOAD`-ed library won't a chance to intercept the calls to `malloc`.
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### How to generate GIMPLE
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If you need to check what gccjit is generating (GIMPLE), then take a look at how to
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generate it in [gimple.md](./doc/gimple.md).
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### How to build a cross-compiling libgccjit
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#### Building libgccjit
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* Follow the instructions on [this repo](https://github.com/cross-cg-gcc-tools/cross-gcc).
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#### Configuring rustc_codegen_gcc
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* Run `./y.sh prepare --cross` so that the sysroot is patched for the cross-compiling case.
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* Set the path to the cross-compiling libgccjit in `gcc-path` (in `config.toml`).
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* Make sure you have the linker for your target (for instance `m68k-unknown-linux-gnu-gcc`) in your `$PATH`. Currently, the linker name is hardcoded as being `$TARGET-gcc`. Specify the target when building the sysroot: `./y.sh build --target-triple m68k-unknown-linux-gnu`.
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* Build your project by specifying the target: `OVERWRITE_TARGET_TRIPLE=m68k-unknown-linux-gnu ../y.sh cargo build --target m68k-unknown-linux-gnu`.
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If the target is not yet supported by the Rust compiler, create a [target specification file](https://docs.rust-embedded.org/embedonomicon/custom-target.html) (note that the `arch` specified in this file must be supported by the rust compiler).
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Then, you can use it the following way:
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* Add the target specification file using `--target` as an **absolute** path to build the sysroot: `./y.sh build --target-triple m68k-unknown-linux-gnu --target $(pwd)/m68k-unknown-linux-gnu.json`
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* Build your project by specifying the target specification file: `OVERWRITE_TARGET_TRIPLE=m68k-unknown-linux-gnu ../y.sh cargo build --target path/to/m68k-unknown-linux-gnu.json`.
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If you get the following error:
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```
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/usr/bin/ld: unrecognised emulation mode: m68kelf
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```
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Make sure you set `gcc-path` (in `config.toml`) to the install directory.
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