[lld] [LLD] [COFF] Make weak aliases to implementations take priority over null pointers (PR #190491)

[Martin Storsjö via llvm-commits]

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@@ -88,10 +88,16 @@ static void checkAndSetWeakAlias(SymbolTable &symtab, InputFile *f,
         // Weak aliases as produced by GCC are named in the form
         // .weak.<weaksymbol>.<othersymbol>, where <othersymbol> is the name
         // of another symbol emitted near the weak symbol.
-        // Just use the definition from the first object file that defined
-        // this weak symbol.
-        if (symtab.ctx.config.allowDuplicateWeak)
+        if (symtab.ctx.config.allowDuplicateWeak) {
+          // If the alias we had points at absolute zero, and we get another
+          // weak symbol which isn't absolute, prefer that one.
+          if (isa<DefinedAbsolute>(u->weakAlias) &&
+              dyn_cast<DefinedAbsolute>(u->weakAlias)->getVA() == 0 &&
+              !isa<DefinedAbsolute>(target)) {
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mstorsjo wrote:

Right, that also probably sounds reasonable. I can update the code to make it do that as well, but I'm not sure if it is warranted to actually add a testcase for that as well, or what do you think?

https://github.com/llvm/llvm-project/pull/190491