[Driver] Improve linking options for target AVR

1. Support user specified linker (-fuse-ld)
2. Support user specified linker script (-T)

Reviewed By: MaskRay, haowei

Differential Revision: https://reviews.llvm.org/D126192

clang/include/clang/Basic/DiagnosticDriverKinds.td

@@ -36,10 +36,6 @@ def warn_drv_avr_mcu_not_specified : Warning<
   "no target microcontroller specified on command line, cannot "
   "link standard libraries, please pass -mmcu=<mcu name>">,
   InGroup<AVRRtlibLinkingQuirks>;
-def warn_drv_avr_gcc_not_found: Warning<
-  "no avr-gcc installation can be found on the system, "
-  "cannot link standard libraries">,
-  InGroup<AVRRtlibLinkingQuirks>;
 def warn_drv_avr_libc_not_found: Warning<
   "no avr-libc installation can be found on the system, "
   "cannot link standard libraries">,

clang/lib/Driver/ToolChains/AVR.cpp

@@ -375,8 +375,7 @@ AVRToolChain::AVRToolChain(const Driver &D, const llvm::Triple &Triple,
 
   // Only add default libraries if the user hasn't explicitly opted out.
   if (!Args.hasArg(options::OPT_nostdlib) &&
-      !Args.hasArg(options::OPT_nodefaultlibs) &&
-      GCCInstallation.isValid()) {
+      !Args.hasArg(options::OPT_nodefaultlibs) && GCCInstallation.isValid()) {
     GCCInstallPath = GCCInstallation.getInstallPath();
     std::string GCCParentPath(GCCInstallation.getParentLibPath());
     getProgramPaths().push_back(GCCParentPath + "/../bin");
@@ -429,9 +428,14 @@ void AVR::Linker::ConstructJob(Compilation &C, const JobAction &JA,
   // Compute information about the target AVR.
   std::string CPU = getCPUName(D, Args, getToolChain().getTriple());
   llvm::Optional<StringRef> FamilyName = GetMCUFamilyName(CPU);
+  llvm::Optional<std::string> AVRLibcRoot = TC.findAVRLibcInstallation();
   llvm::Optional<unsigned> SectionAddressData = GetMCUSectionAddressData(CPU);
 
-  std::string Linker = getToolChain().GetProgramPath(getShortName());
+  // Compute the linker program path, and use GNU "avr-ld" as default.
+  const Arg *A = Args.getLastArg(options::OPT_fuse_ld_EQ);
+  std::string Linker = A ? getToolChain().GetLinkerPath(nullptr)
+                         : getToolChain().GetProgramPath(getShortName());
+
   ArgStringList CmdArgs;
   AddLinkerInputs(getToolChain(), Inputs, Args, CmdArgs, JA);
 
@@ -450,17 +454,11 @@ void AVR::Linker::ConstructJob(Compilation &C, const JobAction &JA,
   if (!Args.hasArg(options::OPT_nostdlib) &&
       !Args.hasArg(options::OPT_nodefaultlibs)) {
     if (!CPU.empty()) {
-        Optional<StringRef> FamilyName = GetMCUFamilyName(CPU);
-        Optional<std::string> AVRLibcRoot = TC.findAVRLibcInstallation();
-
       if (!FamilyName) {
         // We do not have an entry for this CPU in the family
         // mapping table yet.
         D.Diag(diag::warn_drv_avr_family_linking_stdlibs_not_implemented)
             << CPU;
-      } else if (TC.getGCCInstallPath().empty()) {
-        // We can not link since there is no avr-ld.
-        D.Diag(diag::warn_drv_avr_gcc_not_found);
       } else if (!AVRLibcRoot) {
         // No avr-libc found and so no runtime linked.
         D.Diag(diag::warn_drv_avr_libc_not_found);
@@ -473,7 +471,6 @@ void AVR::Linker::ConstructJob(Compilation &C, const JobAction &JA,
         LinkStdlib = true;
       }
     }
-
     if (!LinkStdlib)
       D.Diag(diag::warn_drv_avr_stdlib_not_linked);
   }
@@ -508,11 +505,15 @@ void AVR::Linker::ConstructJob(Compilation &C, const JobAction &JA,
 
     CmdArgs.push_back("--end-group");
 
+    // Add user specified linker script.
+    Args.AddAllArgs(CmdArgs, options::OPT_T);
+
     // Specify the family name as the emulation mode to use.
     // This is almost always required because otherwise avr-ld
     // will assume 'avr2' and warn about the program being larger
     // than the bare minimum supports.
-    CmdArgs.push_back(Args.MakeArgString(std::string("-m") + *FamilyName));
+    if (Linker.find("avr-ld") != std::string::npos)
+      CmdArgs.push_back(Args.MakeArgString(std::string("-m") + *FamilyName));
   }
 
   C.addCommand(std::make_unique<Command>(

clang/test/Driver/avr-toolchain.c

@@ -53,8 +53,22 @@
 // LINKA-NOT: warning: {{.*}} data section address
 
 // RUN: %clang -### --target=avr --sysroot=%S/Inputs/ -mmcu=atmega328 %s 2>&1 | FileCheck --check-prefixes=NOGCC %s
-// NOGCC: warning: no avr-gcc installation can be found on the system, cannot link standard libraries
 // NOGCC: warning: standard library not linked and so no interrupt vector table or compiler runtime routines will be linked
 // NOGCC-NOT: warning: {{.*}} microcontroller
 // NOGCC-NOT: warning: {{.*}} avr-libc
 // NOGCC-NOT: warning: {{.*}} data section address
+
+// RUN: %clang -### --target=avr --sysroot=%S/Inputs/basic_avr_tree -mmcu=atmega328 %s -fuse-ld=avrld 2>&1 | FileCheck --check-prefix=NOLD %s
+// NOLD: error: invalid linker
+
+// RUN: %clang -### --target=avr --sysroot=%S/Inputs/basic_avr_tree -mmcu=atmega328 %s -fuse-ld=%S/Inputs/basic_avr_tree/usr/bin/ld.lld 2>&1 | FileCheck --check-prefix=LLD %s
+// LLD: {{".*lld"}}
+// LLD-NOT: "avr-ld"
+// LLD-NOT: "-mavr5"
+
+// RUN: %clang -### --target=avr --sysroot=%S/Inputs/basic_avr_tree -mmcu=atmega328 %s -T avr.lds 2>&1 | FileCheck --check-prefix=LDS0 %s
+// LDS0: "-T" "avr.lds" "-mavr5"
+
+// RUN: %clang -### --target=avr --sysroot=%S/Inputs/basic_avr_tree -mmcu=atmega328 %s -fuse-ld=%S/Inputs/basic_avr_tree/usr/bin/ld.lld -T avr.lds 2>&1 | FileCheck --check-prefix=LDS1 %s
+// LDS1: "-T" "avr.lds"
+// LDS1-NOT: "-mavr5"