[clang][WebAssembly] Link crt1 even in case of -shared

[yamt]

Summary

This allows -mexec-model=reactor -shared produces a library module
with _initialize entrypoint, which is preferrable over __wasm_call_ctors.

This partially reverts https://reviews.llvm.org/D153293

Discussion: https://github.com/dicej/component-linking-demo/issues/3

[sbc100]

I think we are vearing into somewhat uncharted territory here, but we should probably push forward and document the direction we choose.

Should -shared modules also link with crt1-reactor.o by default then? Or should we add crt1-shared.o and use the whenever -shared is passed. Should we also make -shared incompatible with -mexec-model? It seems like -mexec-model should only apply to the main module, and not to the shared library that it loads.

[yamt]

Should -shared modules also link with crt1-reactor.o by default then? Or should we add crt1-shared.o and use the whenever -shared is passed. Should we also make -shared incompatible with -mexec-model? It seems like -mexec-model should only apply to the main module, and not to the shared library that it loads.

wasi reactor model is for libraries.
i feel it's natural to make it cover shared libraries as well.

but i agree it can be done as you described too.

[yamt]

update test

[yamt]

when -shared, use the reactor model by default

[sbc100]

clang/lib/Driver/ToolChains/WebAssembly.cpp

80–81

LLCM coding style is IsCommand (at last for now: https://llvm.org/docs/Proposals/VariableNames.html)

[yamt]

isCommand -> IsCommand

clang/lib/Driver/ToolChains/WebAssembly.cpp

80–81

oops. fixed. thank you.

[yamt]

can this land?

[sbc100]

(update change title to use the [clang][WebAssembly]convention)

clang/lib/Driver/ToolChains/WebAssembly.cpp

void wasm::Linker::ConstructJob(Compilation &C, const JobAction &JA,
 
   if (Args.hasArg(options::OPT_s))
     CmdArgs.push_back("--strip-all");
 
   Args.AddAllArgs(CmdArgs, options::OPT_L);
   Args.AddAllArgs(CmdArgs, options::OPT_u);
   ToolChain.AddFilePathLibArgs(Args, CmdArgs);
 
-  const char *Crt1 = "crt1.o";
+  bool IsCommand = true;
+  const char *Crt1;
   const char *Entry = nullptr;
 
+  // When -shared is specified, use the reactor exec model unless
+  // specified otherwise.
+  if (Args.hasArg(options::OPT_shared))
+    IsCommand = false;
+
+  if (const Arg *A = Args.getLastArg(options::OPT_mexec_model_EQ)) {
+    StringRef CM = A->getValue();
+    if (CM == "command") {
+      IsCommand = true;
+    } else if (CM == "reactor") {
+      IsCommand = false;
+    } else {
+      ToolChain.getDriver().Diag(diag::err_drv_invalid_argument_to_option)
+          << CM << A->getOption().getName();
+    }
+  }
+
+  if (IsCommand) {
     // If crt1-command.o exists, it supports new-style commands, so use it.
     // Otherwise, use the old crt1.o. This is a temporary transition measure.
     // Once WASI libc no longer needs to support LLVM versions which lack
     // support for new-style command, it can make crt1.o the same as
     // crt1-command.o. And once LLVM no longer needs to support WASI libc
     // versions before that, it can switch to using crt1-command.o.
+    Crt1 = "crt1.o";
     if (ToolChain.GetFilePath("crt1-command.o") != "crt1-command.o")
       Crt1 = "crt1-command.o";
-
-  if (const Arg *A = Args.getLastArg(options::OPT_mexec_model_EQ)) {
-    StringRef CM = A->getValue();
-    if (CM == "command") {
-      // Use default values.
-    } else if (CM == "reactor") {
-      Crt1 = "crt1-reactor.o";
-      Entry = "_initialize";
-    } else {
-      ToolChain.getDriver().Diag(diag::err_drv_invalid_argument_to_option)
-          << CM << A->getOption().getName();
-    }
-  }
-  if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nostartfiles, options::OPT_shared))
+  } else {
+
+  if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nostartfiles))
     CmdArgs.push_back(Args.MakeArgString(ToolChain.GetFilePath(Crt1)));
   if (Entry) {
     CmdArgs.push_back(Args.MakeArgString("--entry"));
     CmdArgs.push_back(Args.MakeArgString(Entry));
   }
 
   if (Args.hasArg(options::OPT_shared))
     CmdArgs.push_back(Args.MakeArgString("-shared"));

clang/test/Driver/wasm-toolchain.c

 
 // A basic C link command-line with known OS.
 
 // RUN: %clang -### --target=wasm32-wasi --sysroot=/foo %s 2>&1 \
 // RUN:   | FileCheck -check-prefix=LINK_KNOWN %s
 // LINK_KNOWN: "-cc1" {{.*}} "-o" "[[temp:[^"]*]]"
 // LINK_KNOWN: wasm-ld{{.*}}" "-L/foo/lib/wasm32-wasi" "crt1.o" "[[temp]]" "-lc" "{{.*[/\\]}}libclang_rt.builtins-wasm32.a" "-o" "a.out"
 
-// -shared should be passed through to `wasm-ld` and not include crt1.o with a known OS.
+// -shared should be passed through to `wasm-ld` and include crt1-reactor.o with a known OS.
 
-// RUN: %clang -### -shared --target=wasm32-wasi --sysroot=/foo %s 2>&1 \
+// RUN: %clang -### -shared -mexec-model=reactor --target=wasm32-wasi --sysroot=/foo %s 2>&1 \
 // RUN:   | FileCheck -check-prefix=LINK_KNOWN_SHARED %s
 // LINK_KNOWN_SHARED: "-cc1" {{.*}} "-o" "[[temp:[^"]*]]"
-// LINK_KNOWN_SHARED: wasm-ld{{.*}}" "-L/foo/lib/wasm32-wasi" "-shared" "[[temp]]" "-lc" "{{.*[/\\]}}libclang_rt.builtins-wasm32.a" "-o" "a.out"
+// LINK_KNOWN_SHARED: wasm-ld{{.*}}" "-L/foo/lib/wasm32-wasi" "crt1-reactor.o" "--entry" "_initialize" "-shared" "[[temp]]" "-lc" "{{.*[/\\]}}libclang_rt.builtins-wasm32.a" "-o" "a.out"
 
-// -shared should be passed through to `wasm-ld` and not include crt1.o with an unknown OS.
+// -shared should be passed through to `wasm-ld` and include crt1-reactor.o with an unknown OS.
 
-// RUN: %clang -### -shared --target=wasm32-unknown-unknown --sysroot=/foo %s 2>&1 \
+// RUN: %clang -### -shared -mexec-model=reactor --target=wasm32-unknown-unknown --sysroot=/foo %s 2>&1 \
 // RUN:   | FileCheck -check-prefix=LINK_UNKNOWN_SHARED %s
 // LINK_UNKNOWN_SHARED: "-cc1" {{.*}} "-o" "[[temp:[^"]*]]"
-// LINK_UNKNOWN_SHARED: wasm-ld{{.*}}" "-shared" "[[temp]]" "-lc" "{{.*[/\\]}}libclang_rt.builtins-wasm32.a" "-o" "a.out"
+// LINK_UNKNOWN_SHARED: wasm-ld{{.*}}" "crt1-reactor.o" "--entry" "_initialize" "-shared" "[[temp]]" "-lc" "{{.*[/\\]}}libclang_rt.builtins-wasm32.a" "-o" "a.out"
 
 // A basic C link command-line with optimization with known OS.
 
 // RUN: %clang -### -O2 --target=wasm32-wasi --sysroot=/foo %s 2>&1 \
 // RUN:   | FileCheck -check-prefix=LINK_OPT_KNOWN %s
 // LINK_OPT_KNOWN: "-cc1" {{.*}} "-o" "[[temp:[^"]*]]"
 // LINK_OPT_KNOWN: wasm-ld{{.*}}" "-L/foo/lib/wasm32-wasi" "crt1.o" "[[temp]]" "-lc" "{{.*[/\\]}}libclang_rt.builtins-wasm32.a" "-o" "a.out"