[WebAssembly] Don't use default GetLinkerPath

[sbc100]

Summary

We can't (don't want to) honor the same set of "-fuse-ld" flags
with WebAssembly since the ELF linkers (ld.lld, ld.gnu, etc) don't
work with wasm object files.

Instead we implement our own linker finding logic, similar or other
non-ELF platforms like MSVC.

We've had a few issues with CLANG_DEFAULT_LINKER overriding the
WebAssembly linker which doesn't make sense since there is no generic
linker that can handle WebAssembly today.

[phosek]

LGTM

clang/lib/Driver/ToolChains/Fuchsia.h

89 ↗

(On Diff #192018)

This seems unrelated?

clang/lib/Driver/ToolChains/MipsLinux.h

51 ↗

(On Diff #192018)

ditto

clang/lib/Driver/ToolChains/WebAssembly.cpp

50 ↗

(On Diff #192018)

I'd also consider handling the else if (UseLinker.empty() || UseLinker == "ld") case which should return the default linker (i.e. wasm-ld), this matches the behavior of the generic driver logic in ToolChain and can be used to select the default linker for the target.

57 ↗

(On Diff #192018)

Nit: you could use getDefaultLinker() instead of hardcoding wasm-ld here so if the name ever changes you only need to change the getter.

[sbc100]

• feedback

[sbc100]

• feedback

[sbc100]

clang/lib/Driver/ToolChains/Fuchsia.h

89 ↗

(On Diff #192018)

You're right.. I shouldn't have tried the sneak that past. This change makes the output of "git grep getDefaultLinker" a lot more useful and confirms with the style guide so might still land it.

clang/lib/Driver/ToolChains/WebAssembly.cpp

57 ↗

(On Diff #192018)

Done. My rational for this was that since the function has exactly one call site (here) it made more sense to keep the information local to its use

[dschuff]

Reverted in rG039be787914610c28cba45c4557454e0a96939ab. Caused a strange error with the waterfall sysroot's build of libcxx: https://logs.chromium.org/logs/wasm/buildbucket/cr-buildbucket.appspot.com/8917800786005174656/+/steps/libcxx/0/stdout

lib/Driver/ToolChains/WebAssembly.h

 namespace tools {
 namespace wasm {
 
 class LLVM_LIBRARY_VISIBILITY Linker : public GnuTool {
 public:
   explicit Linker(const ToolChain &TC);
   bool isLinkJob() const override;
   bool hasIntegratedCPP() const override;
+  std::string getLinkerPath(const llvm::opt::ArgList &Args) const;
   void ConstructJob(Compilation &C, const JobAction &JA,
                     const InputInfo &Output, const InputInfoList &Inputs,
                     const llvm::opt::ArgList &TCArgs,
                     const char *LinkingOutput) const override;
 };
 
 } // end namespace wasm
 } // end namespace tools

lib/Driver/ToolChains/WebAssembly.cpp

 //===--- WebAssembly.cpp - WebAssembly ToolChain Implementation -*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "WebAssembly.h"
 #include "CommonArgs.h"
 #include "clang/Driver/Compilation.h"
 #include "clang/Driver/Driver.h"
 #include "clang/Driver/DriverDiagnostic.h"
 #include "clang/Driver/Options.h"
+#include "llvm/Support/FileSystem.h"
+#include "llvm/Support/Path.h"
 #include "llvm/Option/ArgList.h"
 
 using namespace clang::driver;
 using namespace clang::driver::tools;
 using namespace clang::driver::toolchains;
 using namespace clang;
 using namespace llvm::opt;
 
 wasm::Linker::Linker(const ToolChain &TC)
     : GnuTool("wasm::Linker", "lld", TC) {}
 
 /// Following the conventions in https://wiki.debian.org/Multiarch/Tuples,
 /// we remove the vendor field to form the multiarch triple.
 static std::string getMultiarchTriple(const Driver &D,
                                       const llvm::Triple &TargetTriple,
                                       StringRef SysRoot) {
     return (TargetTriple.getArchName() + "-" +
             TargetTriple.getOSAndEnvironmentName()).str();
 }
 
 bool wasm::Linker::isLinkJob() const { return true; }
 
 bool wasm::Linker::hasIntegratedCPP() const { return false; }
 
+std::string wasm::Linker::getLinkerPath(const ArgList &Args) const {
+  const ToolChain &ToolChain = getToolChain();
+  if (const Arg* A = Args.getLastArg(options::OPT_fuse_ld_EQ)) {
+    StringRef UseLinker = A->getValue();
+    if (!UseLinker.empty()) {
+      if (llvm::sys::path::is_absolute(UseLinker) &&
+          llvm::sys::fs::can_execute(UseLinker))
+        return UseLinker;
+
+      // Accept 'lld', and 'ld' as aliases for the default linker
+      if (UseLinker != "lld" && UseLinker != "ld")
+        ToolChain.getDriver().Diag(diag::err_drv_invalid_linker_name)
+            << A->getAsString(Args);
+    }
+  }
+
+  return ToolChain.getDefaultLinker();
+}
+
 void wasm::Linker::ConstructJob(Compilation &C, const JobAction &JA,
                                 const InputInfo &Output,
                                 const InputInfoList &Inputs,
                                 const ArgList &Args,
                                 const char *LinkingOutput) const {
 
   const ToolChain &ToolChain = getToolChain();
-  const char *Linker = Args.MakeArgString(ToolChain.GetLinkerPath());
+  const char *Linker = Args.MakeArgString(getLinkerPath(Args));
   ArgStringList CmdArgs;
 
   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);

test/Driver/wasm-toolchain.c

 // A basic clang -cc1 command-line. WebAssembly is somewhat special in
 // enabling -fvisibility=hidden by default.
 
 // RUN: %clang %s -### -no-canonical-prefixes -target wasm32-unknown-unknown 2>&1 | FileCheck -check-prefix=CC1 %s
 // CC1: clang{{.*}} "-cc1" "-triple" "wasm32-unknown-unknown" {{.*}} "-fvisibility" "hidden" {{.*}}
 
 // Ditto, but ensure that a user -fvisibility=default disables the default
 // -fvisibility=hidden.
 
 // RUN: %clang %s -### -target wasm32-unknown-unknown -fvisibility=default 2>&1 | FileCheck -check-prefix=FVISIBILITY_DEFAULT %s
 // FVISIBILITY_DEFAULT-NOT: hidden
 
 // A basic C link command-line with unknown OS.
 
-// RUN: %clang -### -no-canonical-prefixes -target wasm32-unknown-unknown --sysroot=/foo -fuse-ld=wasm-ld %s 2>&1 | FileCheck -check-prefix=LINK %s
+// RUN: %clang -### -no-canonical-prefixes -target wasm32-unknown-unknown --sysroot=/foo %s 2>&1 | FileCheck -check-prefix=LINK %s
 // LINK: clang{{.*}}" "-cc1" {{.*}} "-o" "[[temp:[^"]*]]"
 // LINK: wasm-ld{{.*}}" "-L/foo/lib" "crt1.o" "[[temp]]" "-lc" "{{.*[/\\]}}libclang_rt.builtins-wasm32.a" "-o" "a.out"
 
 // A basic C link command-line with optimization with unknown OS.
 
-// RUN: %clang -### -O2 -no-canonical-prefixes -target wasm32-unknown-unknown --sysroot=/foo -fuse-ld=wasm-ld %s 2>&1 | FileCheck -check-prefix=LINK_OPT %s
+// RUN: %clang -### -O2 -no-canonical-prefixes -target wasm32-unknown-unknown --sysroot=/foo %s 2>&1 | FileCheck -check-prefix=LINK_OPT %s
 // LINK_OPT: clang{{.*}}" "-cc1" {{.*}} "-o" "[[temp:[^"]*]]"
 // LINK_OPT: wasm-ld{{.*}}" "-L/foo/lib" "crt1.o" "[[temp]]" "-lc" "{{.*[/\\]}}libclang_rt.builtins-wasm32.a" "-o" "a.out"
 
 // A basic C link command-line with known OS.
 
-// RUN: %clang -### -no-canonical-prefixes -target wasm32-unknown-wasi-musl --sysroot=/foo -fuse-ld=wasm-ld %s 2>&1 | FileCheck -check-prefix=LINK_KNOWN %s
+// RUN: %clang -### -no-canonical-prefixes -target wasm32-unknown-wasi-musl --sysroot=/foo %s 2>&1 | FileCheck -check-prefix=LINK_KNOWN %s
 // LINK_KNOWN: clang{{.*}}" "-cc1" {{.*}} "-o" "[[temp:[^"]*]]"
 // LINK_KNOWN: wasm-ld{{.*}}" "-L/foo/lib/wasm32-wasi-musl" "crt1.o" "[[temp]]" "-lc" "{{.*[/\\]}}libclang_rt.builtins-wasm32.a" "-o" "a.out"
 
 // A basic C link command-line with optimization with known OS.
 
-// RUN: %clang -### -O2 -no-canonical-prefixes -target wasm32-unknown-wasi-musl --sysroot=/foo -fuse-ld=wasm-ld %s 2>&1 | FileCheck -check-prefix=LINK_OPT_KNOWN %s
+// RUN: %clang -### -O2 -no-canonical-prefixes -target wasm32-unknown-wasi-musl --sysroot=/foo %s 2>&1 | FileCheck -check-prefix=LINK_OPT_KNOWN %s
 // LINK_OPT_KNOWN: clang{{.*}}" "-cc1" {{.*}} "-o" "[[temp:[^"]*]]"
 // LINK_OPT_KNOWN: wasm-ld{{.*}}" "-L/foo/lib/wasm32-wasi-musl" "crt1.o" "[[temp]]" "-lc" "{{.*[/\\]}}libclang_rt.builtins-wasm32.a" "-o" "a.out"
 
 // A basic C compile command-line with known OS.
 
 // RUN: %clang -### -no-canonical-prefixes -target wasm32-unknown-wasi-musl --sysroot=/foo %s 2>&1 | FileCheck -check-prefix=COMPILE %s
 // COMPILE: clang{{.*}}" "-cc1" {{.*}} "-internal-isystem" "/foo/include/wasm32-wasi-musl" "-internal-isystem" "/foo/include"
 

test/Driver/wasm-toolchain.cpp

 // A basic clang -cc1 command-line. WebAssembly is somewhat special in
 // enabling -fvisibility=hidden by default.
 
 // RUN: %clangxx %s -### -no-canonical-prefixes -target wasm32-unknown-unknown 2>&1 | FileCheck -check-prefix=CC1 %s
 // CC1: clang{{.*}} "-cc1" "-triple" "wasm32-unknown-unknown" {{.*}} "-fvisibility" "hidden" {{.*}}
 
 // Ditto, but ensure that a user -fvisibility=default disables the default
 // -fvisibility=hidden.
 
 // RUN: %clangxx %s -### -target wasm32-unknown-unknown -fvisibility=default 2>&1 | FileCheck -check-prefix=FVISIBILITY_DEFAULT %s
 // FVISIBILITY_DEFAULT-NOT: hidden
 
 // A basic C++ link command-line with unknown OS.
 
-// RUN: %clangxx -### -no-canonical-prefixes -target wasm32-unknown-unknown --sysroot=/foo -fuse-ld=wasm-ld --stdlib=c++ %s 2>&1 | FileCheck -check-prefix=LINK %s
+// RUN: %clangxx -### -no-canonical-prefixes -target wasm32-unknown-unknown --sysroot=/foo --stdlib=c++ %s 2>&1 | FileCheck -check-prefix=LINK %s
 // LINK: clang{{.*}}" "-cc1" {{.*}} "-o" "[[temp:[^"]*]]"
 // LINK: wasm-ld{{.*}}" "-L/foo/lib" "crt1.o" "[[temp]]" "-lc++" "-lc++abi" "-lc" "{{.*[/\\]}}libclang_rt.builtins-wasm32.a" "-o" "a.out"
 
 // A basic C++ link command-line with optimization with unknown OS.
 
-// RUN: %clangxx -### -O2 -no-canonical-prefixes -target wasm32-unknown-unknown --sysroot=/foo %s --stdlib=c++ -fuse-ld=wasm-ld 2>&1 | FileCheck -check-prefix=LINK_OPT %s
+// RUN: %clangxx -### -O2 -no-canonical-prefixes -target wasm32-unknown-unknown --sysroot=/foo %s --stdlib=c++ 2>&1 | FileCheck -check-prefix=LINK_OPT %s
 // LINK_OPT: clang{{.*}}" "-cc1" {{.*}} "-o" "[[temp:[^"]*]]"
 // LINK_OPT: wasm-ld{{.*}}" "-L/foo/lib" "crt1.o" "[[temp]]" "-lc++" "-lc++abi" "-lc" "{{.*[/\\]}}libclang_rt.builtins-wasm32.a" "-o" "a.out"
 
 // A basic C++ link command-line with known OS.
 
-// RUN: %clangxx -### -no-canonical-prefixes -target wasm32-unknown-wasi-musl --sysroot=/foo -fuse-ld=wasm-ld --stdlib=c++ %s 2>&1 | FileCheck -check-prefix=LINK_KNOWN %s
+// RUN: %clangxx -### -no-canonical-prefixes -target wasm32-unknown-wasi-musl --sysroot=/foo --stdlib=c++ %s 2>&1 | FileCheck -check-prefix=LINK_KNOWN %s
 // LINK_KNOWN: clang{{.*}}" "-cc1" {{.*}} "-o" "[[temp:[^"]*]]"
 // LINK_KNOWN: wasm-ld{{.*}}" "-L/foo/lib/wasm32-wasi-musl" "crt1.o" "[[temp]]" "-lc++" "-lc++abi" "-lc" "{{.*[/\\]}}libclang_rt.builtins-wasm32.a" "-o" "a.out"
 
 // A basic C++ link command-line with optimization with known OS.
 
-// RUN: %clangxx -### -O2 -no-canonical-prefixes -target wasm32-unknown-wasi-musl --sysroot=/foo %s --stdlib=c++ -fuse-ld=wasm-ld 2>&1 | FileCheck -check-prefix=LINK_OPT_KNOWN %s
+// RUN: %clangxx -### -O2 -no-canonical-prefixes -target wasm32-unknown-wasi-musl --sysroot=/foo %s --stdlib=c++ 2>&1 | FileCheck -check-prefix=LINK_OPT_KNOWN %s
 // LINK_OPT_KNOWN: clang{{.*}}" "-cc1" {{.*}} "-o" "[[temp:[^"]*]]"
 // LINK_OPT_KNOWN: wasm-ld{{.*}}" "-L/foo/lib/wasm32-wasi-musl" "crt1.o" "[[temp]]" "-lc++" "-lc++abi" "-lc" "{{.*[/\\]}}libclang_rt.builtins-wasm32.a" "-o" "a.out"
 
 // A basic C++ compile command-line with known OS.
 
 // RUN: %clangxx -### -no-canonical-prefixes -target wasm32-unknown-wasi-musl --sysroot=/foo --stdlib=c++ %s 2>&1 | FileCheck -check-prefix=COMPILE %s
 // COMPILE: clang{{.*}}" "-cc1" {{.*}} "-internal-isystem" "/foo/include/wasm32-wasi-musl/c++/v1" "-internal-isystem" "/foo/include/c++/v1" "-internal-isystem" "/foo/include/wasm32-wasi-musl" "-internal-isystem" "/foo/include"