Mark all functions as DECL_PUBLIC such that they can be linked against. #137
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Generic and As for the linker error in #136, rustc always defines the main shim in the same codegen unit as the rust main function. |
philberty
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Thanks for the review, I have changed this to only apply to the main function and any function with pub visibility. There will be changes to this later on when we start working on the cases you mention. I think this is a middle ground for now to fix the bug. |
| flags |= Backend::function_is_visible; | ||
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| // FIXME need name mangling | ||
| std::string asm_name = function.function_name; |
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The main function doesn't need the name mangling. I mention it here in case you miss it.
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The rust main function needs symbol mangling. Only the main shim doesn't.
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Alright, I see.
In Rust, the main function will be mangling first, then connect to the main shim. And the main shim was generated as a convention automatically.
This is different from C/C++, the main function is always the default symbol linked to _start defined in the linker script.
Thanks for correcting me! @bjorn3
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Yeah, libstd does some extra work in addition to what the libc startup does like setting up a stack guard, adding a handler for SIGSEGV to give a nice error message on stack overflows, storing the program arguments in a static and running the main function within std::panic::catch_unwind to ensure that panicking doesn't immediately abort due to a missing unwind catcher. For reference the main shim calls https://github.com/rust-lang/rust/blob/a2cd91ceb0f156cb442d75e12dc77c3d064cdde4/library/std/src/rt.rs#L60 with the main function as first argument when using libstd. There are also a few other (unstable) options like marking a function with #[start], in which case argc and argv are directly passed to that function without any additional arguments: https://github.com/bjorn3/rustc_codegen_cranelift/blob/3ea8915d4a247b5b3c4cfb3424c230ccd2645b17/example/alloc_example.rs#L30
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Should I open an issue for handling the main shim?
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Should I open an issue for handling the main shim?
Yes @bjorn3 that would be great can you reference this PR in the issue too.
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Thanks for that @bjorn3
This change will need more thought later when it comes to traits and generics etc. Fixes #136
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This will change when we implement visibility but the main method will be reserved case that will always be DECL_PUBLC.
Fixes #136