[AVR][clang] Pass '-fno-use-init-array' to cc1

[mhjacobson]

Summary

On AVR, .ctors is used, not .init_array. Make this the default unless specifically overridden by driver argument.

This matches gcc, and it matches the behavior in (e.g.) the NetBSD driver (for certain OS variants).

[MaskRay]

Looks great!

[mhjacobson]

Thanks!

clang/lib/Driver/ToolChains/AVR.h

 //===--- AVR.h - AVR Tool and ToolChain Implementations ---------*- 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
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_CLANG_LIB_DRIVER_TOOLCHAINS_AVR_H
 #define LLVM_CLANG_LIB_DRIVER_TOOLCHAINS_AVR_H
 
 #include "Gnu.h"
 #include "clang/Driver/InputInfo.h"
-#include "clang/Driver/ToolChain.h"
 #include "clang/Driver/Tool.h"
+#include "clang/Driver/ToolChain.h"
 
 namespace clang {
 namespace driver {
 namespace toolchains {
 
 class LLVM_LIBRARY_VISIBILITY AVRToolChain : public Generic_ELF {
 public:
   AVRToolChain(const Driver &D, const llvm::Triple &Triple,
                const llvm::opt::ArgList &Args);
   void
   AddClangSystemIncludeArgs(const llvm::opt::ArgList &DriverArgs,
                             llvm::opt::ArgStringList &CC1Args) const override;
 
+  void
+  addClangTargetOptions(const llvm::opt::ArgList &DriverArgs,
+                        llvm::opt::ArgStringList &CC1Args,
+                        Action::OffloadKind DeviceOffloadKind) const override;
+
 protected:
   Tool *buildLinker() const override;
 
 private:
   /// Whether libgcc, libct, and friends should be linked.
   ///
   /// This is not done if the user does not specify a
   /// microcontroller on the command line.

clang/lib/Driver/ToolChains/AVR.cpp

if (!AVRLibcRoot.hasValue())
     return;
 
   // Add 'avr-libc/include' to clang system include paths if applicable.
   std::string AVRInc = AVRLibcRoot.getValue() + "/include";
   if (llvm::sys::fs::is_directory(AVRInc))
     addSystemInclude(DriverArgs, CC1Args, AVRInc);
 }
 
+void AVRToolChain::addClangTargetOptions(
+    const llvm::opt::ArgList &DriverArgs, llvm::opt::ArgStringList &CC1Args,
+    Action::OffloadKind DeviceOffloadKind) const {
+  // By default, use `.ctors` (not `.init_array`), as required by libgcc, which
+  // runs constructors/destructors on AVR.
+  if (!DriverArgs.hasFlag(options::OPT_fuse_init_array,
+                          options::OPT_fno_use_init_array, false))
+    CC1Args.push_back("-fno-use-init-array");
+}
+
 Tool *AVRToolChain::buildLinker() const {
   return new tools::AVR::Linker(getTriple(), *this, LinkStdlib);
 }
 
 void AVR::Linker::ConstructJob(Compilation &C, const JobAction &JA,
                                const InputInfo &Output,
                                const InputInfoList &Inputs, const ArgList &Args,
                                const char *LinkingOutput) const {

clang/test/Driver/avr-toolchain.c

 // A basic clang -cc1 command-line.
 
 // RUN: %clang %s -### -no-canonical-prefixes -target avr 2>&1 | FileCheck -check-prefix=CC1 %s
-// CC1: clang{{.*}} "-cc1" "-triple" "avr"
+// CC1: clang{{.*}} "-cc1" "-triple" "avr" {{.*}} "-fno-use-init-array"
 
 // RUN: %clang %s -### -no-canonical-prefixes -target avr --sysroot %S/Inputs/basic_avr_tree 2>&1 | FileCheck -check-prefix CC1A %s
 // CC1A: clang{{.*}} "-cc1" "-triple" "avr" {{.*}} "-internal-isystem" {{".*avr/include"}}
 
 // RUN: %clang %s -### -target avr --sysroot %S/Inputs/basic_avr_tree 2>&1 -nostdinc | FileCheck -check-prefix CC1B %s
 // CC1B-NOT: "-internal-isystem" {{".*avr/include"}}
 
 // RUN: %clang %s -### -target avr --sysroot %S/Inputs/basic_avr_tree 2>&1 -nostdlibinc | FileCheck -check-prefix CC1C %s
 // CC1C-NOT: "-internal-isystem" {{".*avr/include"}}