WebAssembly: do not link with --allow-undefined unconditionally #14069
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In ziglang#1622, when targeting WebAsembly, the --allow-undefined flag became unconditionally added to the linker. This is not always desirable. First, this is error prone. Code with references to unkown symbols will link just fine, but then fail at run-time. This behavior is inconsistent with all other targets. For freestanding wasm applications, and applications that only use WASI, undefined references are better reported at compile-time. This behavior is also inconsistent with clang itself. Autoconf and cmake scripts checking for function presence think that all tested functions exist, but then resulting application cannot run. For example, this is one of the reasons compilation of Ruby 3.2.0 to WASI fails with zig cc, while it works out of the box with clang. But all applications checking for symbol existence before compilation are affected. This reverts the behavior to the one Zig had before ziglang#1622, and introduces an `import_symbols` flag to ignore undefined symbols, assuming that the webassembly runtime will define them.
jedisct1
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breaking
Contributor
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As you may have noticed this change actually requires quite some big changes in the linker, but also in some other areas such as the way we export compiler-rt symbols for the Wasm target (as we need to get rid of the |
Contributor
Author
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Hi @Luukdegram ! Yes, unfortunately these changes are not enough. I got stuck trying to get rid of the |
Contributor
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Got it, I'll try to have something ready by tomorrow :) |
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In #2193, when targeting WebAsembly, the --allow-undefined flag became unconditionally added to the linker.
This is not always desirable.
First, this is error prone. Code with references to unkown symbols will link just fine, but then fail at run-time.
This behavior is inconsistent with all other targets.
For freestanding wasm applications, and applications that only use WASI, undefined references are better reported at compile-time.
This behavior is also inconsistent with clang itself. Autoconf and cmake scripts checking for function presence think that all tested functions exist, but then resulting application cannot run.
For example, this is one of the reasons compilation of Ruby 3.2.0 to WASI fails with zig cc, while it works out of the box with clang. But all applications checking for symbol existence before compilation are affected.
This reverts the behavior to the one Zig had before #2193, and introduces an
import_symbolsflag to ignore undefined symbols, assuming that the webassembly runtime will define them.