New-style command support. #203
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sunfishcode
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The core idea of new-style commands is that all function exports are command entrypoints, and they expect to be called on a fresh instance which lives only for the direction of the call. This is a generalization of the existing `_start` convention, which already has the expectation of a fresh instance which lives only for the direction of the call, and is one of the pieces need to enable user-defined command entrypoints which don't take string arguments and don't return an i32 status code. To show how this works in practice, the following patches implement this new behavior in wasm-ld and wasi-libc: - https://reviews.llvm.org/D81689 - WebAssembly/wasi-libc#203
sbc100
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Jun 12, 2020
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This currently depends on wasm-ld having https://reviews.llvm.org/D81689 in it. Since we're just now dropping support for LLVM 8.0, we'll need to think more about how to manage compatibility here. |
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Should we tag/branch for each major llvm release that we support? |
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Branch/tag sounds difficult if these live a long time and we end up having to backport patches to all the branches. I'm thinking about moving the crt1.c in this PR to crt1-command.c, and restoring the previous crt1.c, so that one libc can support both old and new styles -- the compiler driver would be able to pick which one it wants. I'll investigate this in more detail after https://reviews.llvm.org/D81689 lands. |
This adds a new crt1-command.c startup file, which uses [new-style command support]. Instead of calling `__wasm_call_ctors` and `__wasm_call_dtors` directly, this lets wasm-ld automatically call them. This preserves the existing crt1.c, so that the same wasi-libc build can support old-style and new-style commands, for compatibility during the transition. [new-style command support]: https://reviews.llvm.org/D81689
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https://reviews.llvm.org/D81689 has now landed, and I've now made the change to preserve the existing crt1.c and move the new one into crt1-command.c so that one WASI libc build can support both modes, to avoid the need to depend on the LLVM version. |
whitequark
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Dec 29, 2020
| @@ -276,6 +276,7 @@ _exit | |||
| _flushlbf | |||
| _initialize | |||
| _start | |||
| _start | |||
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Why does _start appear twice now?
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It's defined in crt1.o and crt1-reactor.o. Programs will only use one or the other, but the script which generates defined-symbols.txt doesn't know that.
Dylan-DPC-zz
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Mar 9, 2021
This switches Rust's WASI target to use crt1-command.o instead of crt1.o, which enables support for new-style commands. By default, new-style commands work the same way as old-style commands, so nothing immediately changes here, but this will be needed by later changes to enable support for typed arguments. See here for more information on new-style commands: - WebAssembly/wasi-libc#203 - https://reviews.llvm.org/D81689
Dylan-DPC-zz
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Mar 9, 2021
…chton WASI: Switch to crt1-command.o to enable support for new-style commands This switches Rust's WASI target to use crt1-command.o instead of crt1.o, which enables support for new-style commands. By default, new-style commands work the same way as old-style commands, so nothing immediately changes here, but this will be needed by later changes to enable support for typed arguments. See here for more information on new-style commands: - WebAssembly/wasi-libc#203 - https://reviews.llvm.org/D81689 r? `@alexcrichton`
Dylan-DPC-zz
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Mar 9, 2021
…chton WASI: Switch to crt1-command.o to enable support for new-style commands This switches Rust's WASI target to use crt1-command.o instead of crt1.o, which enables support for new-style commands. By default, new-style commands work the same way as old-style commands, so nothing immediately changes here, but this will be needed by later changes to enable support for typed arguments. See here for more information on new-style commands: - WebAssembly/wasi-libc#203 - https://reviews.llvm.org/D81689 r? ``@alexcrichton``
Dylan-DPC-zz
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Mar 10, 2021
…chton WASI: Switch to crt1-command.o to enable support for new-style commands This switches Rust's WASI target to use crt1-command.o instead of crt1.o, which enables support for new-style commands. By default, new-style commands work the same way as old-style commands, so nothing immediately changes here, but this will be needed by later changes to enable support for typed arguments. See here for more information on new-style commands: - WebAssembly/wasi-libc#203 - https://reviews.llvm.org/D81689 r? ```@alexcrichton```
sunfishcode
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Mar 17, 2022
The core idea of new-style commands is that all function exports are command entrypoints, and they expect to be called on a fresh instance which lives only for the direction of the call. This is a generalization of the existing `_start` convention, which already has the expectation of a fresh instance which lives only for the direction of the call, and is one of the pieces need to enable user-defined command entrypoints which don't take string arguments and don't return an i32 status code. To show how this works in practice, the following patches implement this new behavior in wasm-ld and wasi-libc: - https://reviews.llvm.org/D81689 - WebAssembly/wasi-libc#203
sunfishcode
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Mar 17, 2022
The core idea of new-style commands is that all function exports are command entrypoints, and they expect to be called on a fresh instance which lives only for the direction of the call. This is a generalization of the existing `_start` convention, which already has the expectation of a fresh instance which lives only for the direction of the call, and is one of the pieces need to enable user-defined command entrypoints which don't take string arguments and don't return an i32 status code. To show how this works in practice, the following patches implement this new behavior in wasm-ld and wasi-libc: - https://reviews.llvm.org/D81689 - WebAssembly/wasi-libc#203
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This enables new-style command support. Instead of calling
__wasm_call_ctorsand__wasm_call_dtorsdirectly, this letswasm-ld automatically call them.
And, this comments out a use of "protected" visibility, since
WebAssembly doesn't support it.