[PATCH] D74110: [lld][WebAssembly] Allow symbols with explict import names to be undefined at link time.

[Sam Clegg via Phabricator via llvm-commits]

sbc100 updated this revision to Diff 245549.
sbc100 added a comment.

typo


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D74110/new/

https://reviews.llvm.org/D74110

Files:
  lld/docs/WebAssembly.rst
  lld/test/wasm/import-name.ll
  lld/wasm/Relocations.cpp


Index: lld/wasm/Relocations.cpp
===================================================================
--- lld/wasm/Relocations.cpp
+++ lld/wasm/Relocations.cpp
@@ -28,6 +28,11 @@
   // compiling with -fPIC)
   if (isa<DataSymbol>(sym))
     return false;
+  // Undefined functions with explicit import name are allowed to be undefined
+  // at link time.
+  if (auto* F = dyn_cast<UndefinedFunction>(sym))
+    if (F->importName)
+      return true;
   return (config->allowUndefined ||
           config->allowUndefinedSymbols.count(sym->getName()) != 0);
 }
Index: lld/test/wasm/import-name.ll
===================================================================
--- lld/test/wasm/import-name.ll
+++ lld/test/wasm/import-name.ll
@@ -1,5 +1,5 @@
 ; RUN: llc -filetype=obj %s -o %t.o
-; RUN: wasm-ld --allow-undefined -o %t.wasm %t.o
+; RUN: wasm-ld -o %t.wasm %t.o
 ; RUN: obj2yaml %t.wasm | FileCheck %s
 
 target triple = "wasm32-unknown-unknown"
Index: lld/docs/WebAssembly.rst
===================================================================
--- lld/docs/WebAssembly.rst
+++ lld/docs/WebAssembly.rst
@@ -112,8 +112,8 @@
 a warning.  The ``--fatal-warnings`` flag can be used to disable this behaviour
 and error out if mismatched are found.
 
-Imports and Exports
-~~~~~~~~~~~~~~~~~~~
+Exports
+~~~~~~~
 
 When building a shared library any symbols marked as ``visibility=default`` will
 be exported.
@@ -130,6 +130,17 @@
 used to export symbols in the executable which are marked as
 ``visibility=default``.
 
+Imports
+~~~~~~~
+
+By default no undefined symbols are allowed in the final binary.  The flag
+``--allow-undefined`` results in a WebAssembly import being defined for each
+undefined symbol.  It is then up to the runtime to provide such symbols.
+
+Alternativly symbols can be marked in the source code as with the
+``import_name`` and/or ``import_module`` clang attributes which signals that
+they are expected to be undefined at static link time.
+
 Garbage Collection
 ~~~~~~~~~~~~~~~~~~
 


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