[lld][WebAssembly] Always search *.so for -Bdynamic (#84288)

Search *.so libraries regardless of -pie to make it a bit more
straightforward to build non-pie dynamic-linked executables.

Flip the default to -Bstatic (unless -pie or -shared is specified) as I
think it's what most users expect for the default as of today.
The assumption here is that, because dynamic-linking is not widely used
for WebAssembly, the most users do not specify -Bdynamic or -Bstatic,
expecting static link.
Although the recent wasi-sdk ships *.so files, there are not many wasm
runtimes providing the support of dynamic-linking. (only emscripten and
toywasm as far as i know.)

Author: yamt

lld/wasm/Config.h

@@ -72,7 +72,9 @@ struct Configuration {
   bool stripAll;
   bool stripDebug;
   bool stackFirst;
-  bool isStatic = false;
+  // Because dyamanic linking under Wasm is still experimental we default to
+  // static linking
+  bool isStatic = true;
   bool trace;
   uint64_t globalBase;
   uint64_t initialHeap;

lld/wasm/Driver.cpp

@@ -341,9 +341,7 @@ static std::optional<std::string> findFromSearchPaths(StringRef path) {
 // search paths.
 static std::optional<std::string> searchLibraryBaseName(StringRef name) {
   for (StringRef dir : config->searchPaths) {
-    // Currently we don't enable dynamic linking at all unless -shared or -pie
-    // are used, so don't even look for .so files in that case..
-    if (ctx.isPic && !config->isStatic)
+    if (!config->isStatic)
       if (std::optional<std::string> s = findFile(dir, "lib" + name + ".so"))
         return s;
     if (std::optional<std::string> s = findFile(dir, "lib" + name + ".a"))
@@ -556,6 +554,10 @@ static void readConfigs(opt::InputArgList &args) {
   config->zStackSize =
       args::getZOptionValue(args, OPT_z, "stack-size", WasmPageSize);
 
+  // -Bdynamic by default if -pie or -shared is specified.
+  if (config->pie || config->shared)
+    config->isStatic = false;
+
   if (config->maxMemory != 0 && config->noGrowableMemory) {
     // Erroring out here is simpler than defining precedence rules.
     error("--max-memory is incompatible with --no-growable-memory");

lld/wasm/Options.td

@@ -38,9 +38,9 @@ multiclass B<string name, string help1, string help2> {
 // The following flags are shared with the ELF linker
 def Bsymbolic: F<"Bsymbolic">, HelpText<"Bind defined symbols locally">;
 
-def Bdynamic: F<"Bdynamic">, HelpText<"Link against shared libraries (default)">;
+def Bdynamic: F<"Bdynamic">, HelpText<"Link against shared libraries">;
 
-def Bstatic: F<"Bstatic">, HelpText<"Do not link against shared libraries">;
+def Bstatic: F<"Bstatic">, HelpText<"Do not link against shared libraries (default)">;
 
 def build_id: F<"build-id">, HelpText<"Alias for --build-id=fast">;