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Wasm,libc: fix wasm-ld failure in matching libc symbols.

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Signed-off-by: Takeshi Yoneda <takeshi@tetrate.io>
This commit is contained in:
Takeshi Yoneda 2021-07-02 15:20:17 +09:00 committed by Andrew Kelley
parent 24bfd7bddd
commit a9a4fd3200
1 changed files with 18 additions and 1 deletions
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19
src/stage1/codegen.cpp
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@ -428,8 +428,18 @@ static LLVMValueRef make_fn_llvm_value(CodeGen *g, ZigFn *fn) {
// compiler as we're telling LLVM (using 'wasm-import-name' and
// 'wasm-import-name') what the real function name is and where to find
// it.
const bool use_mangled_name = target_is_wasm(g->zig_target) &&
bool use_mangled_name = target_is_wasm(g->zig_target) &&
fn_proto->is_extern && fn_proto->lib_name != nullptr;
// This is subtle but important to match libc symbols at static link time correctly.
// We treat "c" lib_name as a special library indicating that it should be defined
// in libc. But if we mangle a libc symbol name here with "c" module name, then wasm-ld cannot resolve
// the symbol. This is because at the static link time with wasm-ld, the linker does not
// take module names into account, and instead looking for a pure symbol name (i.e. function name)
// written into the ".linking" custom section (i.e. it does not use import section).
// This is the intended behavior of wasm-ld, because Wasm has a concept of host functions,
// which are undefined functions supposed to be resolved by host runtimes *with module names*
// at load times even if it is "static linked" with the linker.
use_mangled_name = use_mangled_name && (strcmp(buf_ptr(fn_proto->lib_name), "c") != 0);
// Pick a weird name to avoid collisions...
// This whole function should be burned to the ground.
Buf *mangled_symbol_buf = use_mangled_name ?
@ -452,6 +462,13 @@ static LLVMValueRef make_fn_llvm_value(CodeGen *g, ZigFn *fn) {
llvm_fn = LLVMAddFunction(g->module, symbol_name, fn_llvm_type);
if (use_mangled_name) {
// Note that "wasm-import-module"ed symbols will not be resolved
// in the future version of wasm-ld since the attribute basically means that
// "the symbol should be resolved at load time by runtimes", though
// the symbol is already mangled here and it is written into "linking" section
// used by wasm-ld to match symbols, so it should not be expected by users.
// tl;dr is that users should not put the lib_name specifier on extern statements
// if they want to link symbols with wasm-ld.
addLLVMFnAttrStr(llvm_fn, "wasm-import-name", unmangled_name);
addLLVMFnAttrStr(llvm_fn, "wasm-import-module", buf_ptr(fn_proto->lib_name));
}