[WebAssembly] Implement "Reactor" mode

[sunfish]

Summary

This is an experimental patch which adds a -mexec-model= command-line flag. The default value is "command" which is no change from the current behavior. The other option is "reactor" which enables an experimental Reactor ABI.

By default, clang/LLVM don't do much differently for Reactors -- it just picks a different crt1.o and entry point name -- so I won't go into detail here. I'll open a PR for wasi-libc to add the libc side of this, and I'll describe the ABI in detail there, and I expect most of the discussion will happen there.

[sunfish]

The wasi-libc PR is here.

[sbc100]

Add a test case to clang/test/Driver/wasm-toolchain.c?

clang/lib/Driver/ToolChains/WebAssembly.cpp

88

Maybe call this Crt1 so it doesn't looks so much like crtZero?

92

I have a slight preference for crt1-foo.o over foo-crt1.o. But I've tell where that preference comes from :)

96

Shouldn't this be nullptr?

Also, maybe move the if Entry block inside this condition so this line can declare entry avoid the extra declaration above?

102

I assume that all he users -Wl args come after.. so its still possible to set --entry on the command line?

[sbc100]

lgtm with some comments

[sunfish]

Rebase, update, add a test, and add basic error reporting.

[sunfish]

This addresses the review feedback from earlier. To answer this question:

I assume that all he users -Wl args come after.. so its still possible to set --entry on the command line?

Yes, that is what happens.

[bjope]

clang/test/Driver/wasm-toolchain.c

116

This isn't working for me on redhat 7 servers. I get

"wasm-ld" "-L/lib" "/lib/crt1.o" ...

No idea why I get the full patch to crt1.o. But it's not matching with the FileCheck pattern.

[bjope]

clang/test/Driver/wasm-toolchain.c

116

/full patch/full path/

[sunfish]

clang/test/Driver/wasm-toolchain.c

116

Would you be able to test whether the following patch fixes it?

diff
diff --git a/clang/test/Driver/wasm-toolchain.c b/clang/test/Driver/wasm-toolchain.c
index 8300a81614e..332e6048cc5 100644
--- a/clang/test/Driver/wasm-toolchain.c
+++ b/clang/test/Driver/wasm-toolchain.c
@@ -110,11 +110,11 @@

 // Basic exec-model tests.

-// RUN: %clang %s -### -no-canonical-prefixes -target wasm32-unknown-unknown -mexec-model=command 2>&1 \
+// RUN: %clang %s -### -no-canonical-prefixes -target wasm32-unknown-unknown --sysroot=%s/no-sysroot-there -mexec-model=command 2>&1 \
 // RUN:   | FileCheck -check-prefix=CHECK-COMMAND %s
 // CHECK-COMMAND: clang{{.*}}" "-cc1" {{.*}} "-o" "[[temp:[^"]*]]"
 // CHECK-COMMAND: wasm-ld{{.*}}" "crt1.o" "[[temp]]" "-lc" "{{.*[/\\]}}libclang_rt.builtins-wasm32.a" "-o" "a.out"

-// RUN: %clang %s -### -no-canonical-prefixes -target wasm32-unknown-unknown -mexec-model=reactor 2>&1 \
+// RUN: %clang %s -### -no-canonical-prefixes -target wasm32-unknown-unknown --sysroot=%s/no-sysroot-there -mexec-model=reactor 2>&1 \
 // RUN:   | FileCheck -check-prefix=CHECK-REACTOR %s
 // CHECK-REACTOR: wasm-ld{{.*}}" {{.*}} "--entry" "_initialize" {{.*}}

[bjope]

clang/test/Driver/wasm-toolchain.c

116

Yes, that is working.

[sunfish]

clang/test/Driver/wasm-toolchain.c

116

Thanks for confirming! I've now committed this fix.

clang/docs/ClangCommandLineReference.rst

 .. option:: -msign-ext, -mno-sign-ext
 
 .. option:: -msimd128, -mno-simd128
 
 .. option:: -mtail-call, -mno-tail-call
 
 .. option:: -munimplemented-simd128, -mno-unimplemented-simd128
 
+.. option:: -mexec-model=<arg>
+
+Select between "command" and "reactor" executable models. Commands have a main
+function which scopes the lifetime of the program. Reactors are activated and
+remain active until explicitly terminated.
+
 X86
 ---
 .. option:: -m3dnow, -mno-3dnow
 
 .. option:: -m3dnowa, -mno-3dnowa
 
 .. option:: -madx, -mno-adx
 

clang/include/clang/Driver/Options.td

 def m_hexagon_Features_HVX_Group : OptionGroup<"<hexagon features group>">,
                                    Group<m_Group>, DocName<"Hexagon">;
 def m_mips_Features_Group : OptionGroup<"<mips features group>">,
                             Group<m_Group>, DocName<"MIPS">;
 def m_ppc_Features_Group : OptionGroup<"<ppc features group>">,
                            Group<m_Group>, DocName<"PowerPC">;
 def m_wasm_Features_Group : OptionGroup<"<wasm features group>">,
                             Group<m_Group>, DocName<"WebAssembly">;
+// The features added by this group will not be added to target features.
+// These are explicitly handled.
+def m_wasm_Features_Driver_Group : OptionGroup<"<wasm driver features group>">,
+                                   Group<m_Group>, DocName<"WebAssembly Driver">;
 def m_x86_Features_Group : OptionGroup<"<x86 features group>">,
                            Group<m_Group>, Flags<[CoreOption]>, DocName<"X86">;
 def m_riscv_Features_Group : OptionGroup<"<riscv features group>">,
                              Group<m_Group>, DocName<"RISCV">;
 
 def m_libc_Group : OptionGroup<"<m libc group>">, Group<m_mips_Features_Group>,
                    Flags<[HelpHidden]>;
 

 def mmutable_globals : Flag<["-"], "mmutable-globals">, Group<m_wasm_Features_Group>;
 def mno_mutable_globals : Flag<["-"], "mno-mutable-globals">, Group<m_wasm_Features_Group>;
 def mmultivalue : Flag<["-"], "mmultivalue">, Group<m_wasm_Features_Group>;
 def mno_multivalue : Flag<["-"], "mno-multivalue">, Group<m_wasm_Features_Group>;
 def mtail_call : Flag<["-"], "mtail-call">, Group<m_wasm_Features_Group>;
 def mno_tail_call : Flag<["-"], "mno-tail-call">, Group<m_wasm_Features_Group>;
 def mreference_types : Flag<["-"], "mreference-types">, Group<m_wasm_Features_Group>;
 def mno_reference_types : Flag<["-"], "mno-reference-types">, Group<m_wasm_Features_Group>;
+def mexec_model_EQ : Joined<["-"], "mexec-model=">, Group<m_wasm_Features_Driver_Group>,
+                     Values<"command,reactor">,
+                     HelpText<"Execution model (WebAssembly only)">;
 
 def mamdgpu_debugger_abi : Joined<["-"], "mamdgpu-debugger-abi=">,
   Flags<[HelpHidden]>,
   Group<m_Group>,
   HelpText<"Generate additional code for specified <version> of debugger ABI (AMDGPU only)">,
   MetaVarName<"<version>">;
 
 def mcode_object_v3 : Flag<["-"], "mcode-object-v3">, Group<m_amdgpu_Features_Group>,

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";
+  const char *Entry = NULL;
+  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))
-    CmdArgs.push_back(Args.MakeArgString(ToolChain.GetFilePath("crt1.o")));
+    CmdArgs.push_back(Args.MakeArgString(ToolChain.GetFilePath(Crt1)));
+  if (Entry) {
+    CmdArgs.push_back(Args.MakeArgString("--entry"));
+    CmdArgs.push_back(Args.MakeArgString(Entry));
+  }
 
   AddLinkerInputs(ToolChain, Inputs, Args, CmdArgs, JA);
 
   if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nodefaultlibs)) {
     if (ToolChain.ShouldLinkCXXStdlib(Args))
       ToolChain.AddCXXStdlibLibArgs(Args, CmdArgs);
 
     if (Args.hasArg(options::OPT_pthread)) {
       CmdArgs.push_back("-lpthread");
       CmdArgs.push_back("--shared-memory");
     }
 
     CmdArgs.push_back("-lc");
     AddRunTimeLibs(ToolChain, ToolChain.getDriver(), CmdArgs, Args);
   }
 
   CmdArgs.push_back("-o");
   CmdArgs.push_back(Output.getFilename());
 

clang/test/Driver/wasm-toolchain.c

 // RUN: %clang -### -no-canonical-prefixes -target wasm32-unknown-unknown \
 // RUN:     --sysroot=/foo %s -fwasm-exceptions -mllvm -enable-emscripten-cxx-exceptions 2>&1 \
 // RUN:   | FileCheck -check-prefix=WASM_EXCEPTIONS_EMSCRIPTEN_EH %s
 // WASM_EXCEPTIONS_EMSCRIPTEN_EH: invalid argument '-fwasm-exceptions' not allowed with '-mllvm -enable-emscripten-cxx-exceptions'
 
 // RUN: %clang %s -### -fsanitize=address -target wasm32-unknown-emscripten 2>&1 | FileCheck -check-prefix=CHECK-ASAN-EMSCRIPTEN %s
 // CHECK-ASAN-EMSCRIPTEN: "-fsanitize=address"
 // CHECK-ASAN-EMSCRIPTEN: "-fsanitize-address-globals-dead-stripping"
+
+// Basic exec-model tests.
+
+// RUN: %clang %s -### -no-canonical-prefixes -target wasm32-unknown-unknown -mexec-model=command 2>&1 \
+// RUN:   | FileCheck -check-prefix=CHECK-COMMAND %s
+// CHECK-COMMAND: clang{{.*}}" "-cc1" {{.*}} "-o" "[[temp:[^"]*]]"
+// CHECK-COMMAND: wasm-ld{{.*}}" "crt1.o" "[[temp]]" "-lc" "{{.*[/\\]}}libclang_rt.builtins-wasm32.a" "-o" "a.out"
+
+// RUN: %clang %s -### -no-canonical-prefixes -target wasm32-unknown-unknown -mexec-model=reactor 2>&1 \
+// RUN:   | FileCheck -check-prefix=CHECK-REACTOR %s
+// CHECK-REACTOR: wasm-ld{{.*}}" {{.*}} "--entry" "_initialize" {{.*}}