[lld][WebAssembly] Add allow-multiple-definition flag

lld/test/wasm/Inputs/allow-multiple-definition.s

@@ -0,0 +1,6 @@
+ .hidden foo
+ .globl foo
+foo:
+ .functype foo () -> (i32)
+ i32.const 1
+ end_function

lld/test/wasm/allow-multiple-definition.s

@@ -0,0 +1,38 @@
+# RUN: llvm-mc -filetype=obj -triple=wasm32-unknown-unknown %s -o %t1
+# RUN: llvm-mc -filetype=obj -triple=wasm32-unknown-unknown %p/Inputs/allow-multiple-definition.s -o %t2
+# RUN: not wasm-ld %t1 %t2 -o /dev/null
+# RUN: not wasm-ld --allow-multiple-definition --no-allow-multiple-definition %t1 %t2 -o /dev/null
+# RUN: wasm-ld --allow-multiple-definition --fatal-warnings %t1 %t2 -o %t3
+# RUN: wasm-ld --allow-multiple-definition --fatal-warnings %t2 %t1 -o %t4
+# RUN: llvm-objdump --no-print-imm-hex -d %t3 | FileCheck %s
+# RUN: llvm-objdump --no-print-imm-hex -d %t4 | FileCheck --check-prefix=REVERT %s
+
+# RUN: wasm-ld --noinhibit-exec %t2 %t1 -o /dev/null 2>&1 | FileCheck %s --check-prefix=WARN
+# WARN: warning: duplicate symbol: foo
+
+# RUN: wasm-ld -z muldefs --fatal-warnings %t1 %t2 -o %t3
+# RUN: wasm-ld -z muldefs --fatal-warnings %t2 %t1 -o %t4
+# RUN: llvm-objdump --no-print-imm-hex -d %t3 | FileCheck %s
+# RUN: llvm-objdump --no-print-imm-hex -d %t4 | FileCheck --check-prefix=REVERT %s
+
+# CHECK: i32.const 0
+# REVERT: i32.const 1
+
+# inputs contain different constants for function foo return.
+# Tests below checks that order of files in command line
+# affects on what symbol will be used.
+# If flag allow-multiple-definition is enabled the first
+# meet symbol should be used.
+
+ .hidden foo
+ .globl foo
+foo:
+ .functype foo () -> (i32)
+ i32.const 0
+ end_function
+
+ .globl _start
+_start:
+ .functype _start () -> (i32)
+ call foo
+ end_function

lld/wasm/Config.h

@@ -12,6 +12,7 @@
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/StringSet.h"
+#include "llvm/ADT/Twine.h"
 #include "llvm/BinaryFormat/Wasm.h"
 #include "llvm/Support/CachePruning.h"
 #include <optional>
@@ -43,6 +44,7 @@ enum class BuildIdKind { None, Fast, Sha1, Hexstring, Uuid };
 // and such fields have the same name as the corresponding options.
 // Most fields are initialized by the driver.
 struct Configuration {
+ bool allowMultipleDefinition;
  bool bsymbolic;
  bool checkFeatures;
  bool compressRelocations;
@@ -64,6 +66,7 @@ struct Configuration {
  bool importUndefined;
  std::optional<bool> is64;
  bool mergeDataSegments;
+ bool noinhibitExec;
  bool pie;
  bool printGcSections;
  bool relocatable;
@@ -148,6 +151,8 @@ struct Ctx {
 
 extern Ctx ctx;
 
+void errorOrWarn(const llvm::Twine &msg);
+
 } // namespace lld::wasm
 
 #endif

lld/wasm/Driver.cpp

@@ -47,6 +47,13 @@ namespace lld::wasm {
 Configuration *config;
 Ctx ctx;
 
+void errorOrWarn(const llvm::Twine &msg) {
+ if (config->noinhibitExec)
+ warn(msg);
+ else
+ error(msg);
+}
+
 void Ctx::reset() {
  objectFiles.clear();
  stubFiles.clear();
@@ -99,6 +106,16 @@ class LinkerDriver {
 
  std::vector<InputFile *> files;
 };
+
+static bool hasZOption(opt::InputArgList &args, StringRef key) {
+ bool ret = false;
+ for (const auto *arg : args.filtered(OPT_z))
+ if (key == arg->getValue()) {
+ ret = true;
+ arg->claim();
+ }
+ return ret;
+}
 } // anonymous namespace
 
 bool link(ArrayRef<const char *> args, llvm::raw_ostream &stdoutOS,
@@ -467,6 +484,10 @@ getBuildId(opt::InputArgList &args) {
 
 // Initializes Config members by the command line options.
 static void readConfigs(opt::InputArgList &args) {
+ config->allowMultipleDefinition =
+ hasZOption(args, "muldefs") ||
+ args.hasFlag(OPT_allow_multiple_definition,
+ OPT_no_allow_multiple_definition, false);
  config->bsymbolic = args.hasArg(OPT_Bsymbolic);
  config->checkFeatures =
  args.hasFlag(OPT_check_features, OPT_no_check_features, true);
@@ -479,6 +500,7 @@ static void readConfigs(opt::InputArgList &args) {
  config->exportAll = args.hasArg(OPT_export_all);
  config->exportTable = args.hasArg(OPT_export_table);
  config->growableTable = args.hasArg(OPT_growable_table);
+ config->noinhibitExec = args.hasArg(OPT_noinhibit_exec);
 
  if (args.hasArg(OPT_import_memory_with_name)) {
  config->memoryImport =
@@ -1162,7 +1184,7 @@ static void splitSections() {
 
 static bool isKnownZFlag(StringRef s) {
  // For now, we only support a very limited set of -z flags
- return s.starts_with("stack-size=");
+ return s.starts_with("stack-size=") || s.starts_with("muldefs");
 }
 
 // Report a warning for an unknown -z option.

lld/wasm/Options.td

@@ -42,6 +42,10 @@ def Bdynamic: F<"Bdynamic">, HelpText<"Link against shared libraries">;
 
 def Bstatic: F<"Bstatic">, HelpText<"Do not link against shared libraries (default)">;
 
+defm allow_multiple_definition: B<"allow-multiple-definition",
+ "Allow multiple definitions",
+ "Do not allow multiple definitions (default)">;
+
 def build_id: F<"build-id">, HelpText<"Alias for --build-id=fast">;
 
 def build_id_eq: J<"build-id=">, HelpText<"Generate build ID note">,
@@ -105,6 +109,9 @@ defm mllvm: Eq<"mllvm", "Additional arguments to forward to LLVM's option proces
 
 defm Map: Eq<"Map", "Print a link map to the specified file">;
 
+def noinhibit_exec: F<"noinhibit-exec">,
+ HelpText<"Retain the executable output file whenever it is still usable">;
+
 def o: JoinedOrSeparate<["-"], "o">, MetaVarName<"<path>">,
  HelpText<"Path to file to write output">;
 

lld/wasm/SymbolTable.cpp

@@ -319,9 +319,12 @@ static bool shouldReplace(const Symbol *existing, InputFile *newFile,
  }
 
  // Neither symbol is week. They conflict.
- error("duplicate symbol: " + toString(*existing) + "\n>>> defined in " +
- toString(existing->getFile()) + "\n>>> defined in " +
- toString(newFile));
+ if (config->allowMultipleDefinition)
+ return false;
+
+ errorOrWarn("duplicate symbol: " + toString(*existing) + "\n>>> defined in " +
+ toString(existing->getFile()) + "\n>>> defined in " +
+ toString(newFile));
  return true;
 }