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| # How to debug GCC LTO | ||
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| Run do the command with `-v -save-temps` and then extract the `lto1` line from the output and run that under the debugger. |
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| # Debugging libgccjit | ||
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| Sometimes, libgccjit will crash and output an error like this: | ||
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| ``` | ||
| during RTL pass: expand | ||
| libgccjit.so: error: in expmed_mode_index, at expmed.h:249 | ||
| 0x7f0da2e61a35 expmed_mode_index | ||
| ../../../gcc/gcc/expmed.h:249 | ||
| 0x7f0da2e61aa4 expmed_op_cost_ptr | ||
| ../../../gcc/gcc/expmed.h:271 | ||
| 0x7f0da2e620dc sdiv_cost_ptr | ||
| ../../../gcc/gcc/expmed.h:540 | ||
| 0x7f0da2e62129 sdiv_cost | ||
| ../../../gcc/gcc/expmed.h:558 | ||
| 0x7f0da2e73c12 expand_divmod(int, tree_code, machine_mode, rtx_def*, rtx_def*, rtx_def*, int) | ||
| ../../../gcc/gcc/expmed.c:4335 | ||
| 0x7f0da2ea1423 expand_expr_real_2(separate_ops*, rtx_def*, machine_mode, expand_modifier) | ||
| ../../../gcc/gcc/expr.c:9240 | ||
| 0x7f0da2cd1a1e expand_gimple_stmt_1 | ||
| ../../../gcc/gcc/cfgexpand.c:3796 | ||
| 0x7f0da2cd1c30 expand_gimple_stmt | ||
| ../../../gcc/gcc/cfgexpand.c:3857 | ||
| 0x7f0da2cd90a9 expand_gimple_basic_block | ||
| ../../../gcc/gcc/cfgexpand.c:5898 | ||
| 0x7f0da2cdade8 execute | ||
| ../../../gcc/gcc/cfgexpand.c:6582 | ||
| ``` | ||
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| To see the code which causes this error, call the following function: | ||
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| ```c | ||
| gcc_jit_context_dump_to_file(ctxt, "/tmp/output.c", 1 /* update_locations */) | ||
| ``` | ||
| This will create a C-like file and add the locations into the IR pointing to this C file. | ||
| Then, rerun the program and it will output the location in the second line: | ||
| ``` | ||
| libgccjit.so: /tmp/something.c:61322:0: error: in expmed_mode_index, at expmed.h:249 | ||
| ``` | ||
| Or add a breakpoint to `add_error` in gdb and print the line number using: | ||
| ``` | ||
| p loc->m_line | ||
| p loc->m_filename->m_buffer | ||
| ``` | ||
| To print a debug representation of a tree: | ||
| ```c | ||
| debug_tree(expr); | ||
| ``` | ||
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| (defined in print-tree.h) | ||
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| To print a debug representation of a gimple struct: | ||
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| ```c | ||
| debug_gimple_stmt(gimple_struct) | ||
| ``` | ||
| To get the `rustc` command to run in `gdb`, add the `--verbose` flag to `cargo build`. | ||
| To have the correct file paths in `gdb` instead of `/usr/src/debug/gcc/libstdc++-v3/libsupc++/eh_personality.cc`: | ||
| Maybe by calling the following at the beginning of gdb: | ||
| ``` | ||
| set substitute-path /usr/src/debug/gcc /path/to/gcc-repo/gcc | ||
| ``` | ||
| TODO(antoyo): but that's not what I remember I was doing. |
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| # Common errors | ||
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| This file lists errors that were encountered and how to fix them. | ||
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| ### `failed to build archive` error | ||
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| When you get this error: | ||
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| ``` | ||
| error: failed to build archive: failed to open object file: No such file or directory (os error 2) | ||
| ``` | ||
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| That can be caused by the fact that you try to compile with `lto = "fat"`, but you didn't compile the sysroot with LTO. | ||
| (Not sure if that's the reason since I cannot reproduce anymore. Maybe it happened when forgetting setting `FAT_LTO`.) | ||
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| ### ld: cannot find crtbegin.o | ||
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| When compiling an executable with libgccijt, if setting the `*LIBRARY_PATH` variables to the install directory, you will get the following errors: | ||
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| ``` | ||
| ld: cannot find crtbegin.o: No such file or directory | ||
| ld: cannot find -lgcc: No such file or directory | ||
| ld: cannot find -lgcc: No such file or directory | ||
| libgccjit.so: error: error invoking gcc driver | ||
| ``` | ||
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| To fix this, set the variables to `gcc-build/build/gcc`. |
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| # Tips | ||
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| The following shows how to do different random small things we encountered and thought could | ||
| be useful. | ||
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| ### How to send arguments to the GCC linker | ||
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| ``` | ||
| CG_RUSTFLAGS="-Clink-args=-save-temps -v" ../y.sh cargo build | ||
| ``` | ||
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| ### How to see the personality functions in the asm dump | ||
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| ``` | ||
| CG_RUSTFLAGS="-Clink-arg=-save-temps -v -Clink-arg=-dA" ../y.sh cargo build | ||
| ``` | ||
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| ### How to see the LLVM IR for a sysroot crate | ||
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| ``` | ||
| cargo build -v --target x86_64-unknown-linux-gnu -Zbuild-std | ||
| # Take the command from the output and add --emit=llvm-ir | ||
| ``` | ||
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| ### To prevent the linker from unmangling symbols | ||
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| Run with: | ||
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| ``` | ||
| COLLECT_NO_DEMANGLE=1 | ||
| ``` | ||
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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`). | ||
| * 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 | ||
| 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. | ||
| * Set the path to the cross-compiling libgccjit in `gcc-path` (in `config.toml`). | ||
| * 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`. | ||
| * 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). | ||
| 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` | ||
| * 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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| ``` | ||
| /usr/bin/ld: unrecognised emulation mode: m68kelf | ||
| ``` | ||
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| Make sure you set `gcc-path` (in `config.toml`) to the install directory. |