[Driver] Include crt0.o in the baremetal link (#101258)

The common baremetal libc implementations already provide crt0.o and GCC
automatically links it so this improves parity.

Author: petrhosek

clang/lib/Driver/ToolChains/BareMetal.cpp

@@ -487,6 +487,11 @@ void baremetal::Linker::ConstructJob(Compilation &C, const JobAction &JA,
     CmdArgs.push_back(Arch == llvm::Triple::aarch64_be ? "-EB" : "-EL");
   }
 
+  if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nostartfiles,
+                   options::OPT_r)) {
+    CmdArgs.push_back(Args.MakeArgString(TC.GetFilePath("crt0.o")));
+  }
+
   Args.addAllArgs(CmdArgs, {options::OPT_L, options::OPT_T_Group,
                             options::OPT_s, options::OPT_t, options::OPT_r});
 

clang/test/Driver/Inputs/baremetal_arm/lib/crt0.o

@@ -16,6 +16,7 @@
 // CHECK-V6M-C-SAME: "-internal-isystem" "[[SYSROOT]]{{[/\\]+}}include"
 // CHECK-V6M-C-SAME: "-x" "c++" "{{.*}}baremetal.cpp"
 // CHECK-V6M-C-NEXT: ld{{(.exe)?}}" "{{.*}}.o" "-Bstatic" "-EL"
+// CHECK-V6M-C-SAME: "[[SYSROOT:[^"]+]]{{[/\\]+}}lib{{[/\\]+}}crt0.o"
 // CHECK-V6M-C-SAME: "-T" "semihosted.lds" "-Lsome{{[/\\]+}}directory{{[/\\]+}}user{{[/\\]+}}asked{{[/\\]+}}for"
 // CHECK-V6M-C-SAME: "-L[[SYSROOT:[^"]+]]{{[/\\]+}}lib"
 // CHECK-V6M-C-SAME: "-lc" "-lm" "{{[^"]*}}libclang_rt.builtins.a" "--target2=rel" "-o" "{{.*}}.tmp.out"
@@ -37,6 +38,7 @@
 // CHECK-V6M-TREE-SAME: "-internal-isystem" "[[INSTALLED_DIR]]{{[/\\]+}}..{{[/\\]+}}include{{[/\\]+}}armv6m-unknown-none-eabi"
 // CHECK-V6M-TREE-SAME: "-x" "c++" "{{.*}}baremetal.cpp"
 // CHECK-V6M-TREE-NEXT: ld{{(.exe)?}}" "{{.*}}.o" "-Bstatic" "-EL"
+// CHECK-V6M-TREE-SAME: "[[INSTALLED_DIR]]{{[/\\]+}}..{{[/\\]+}}lib{{[/\\]+}}armv6m-unknown-none-eabi{{[/\\]+}}crt0.o"
 // CHECK-V6M-TREE-SAME: "-L[[INSTALLED_DIR]]{{[/\\]+}}..{{[/\\]+}}lib{{[/\\]+}}armv6m-unknown-none-eabi"
 // CHECK-V6M-TREE-SAME: "-lc" "-lm" "{{[^"]*}}libclang_rt.builtins.a" "--target2=rel" "-o" "{{.*}}.tmp.out"
 
@@ -48,6 +50,7 @@
 // CHECK-ARMV7M-PER-TARGET: "-isysroot" "[[SYSROOT:[^"]*]]"
 // CHECK-ARMV7M-PER-TARGET: "-x" "c++" "{{.*}}baremetal.cpp"
 // CHECK-ARMV7M-PER-TARGET: ld{{(.exe)?}}" "{{.*}}.o" "-Bstatic" "-EL"
+// CHECK-ARMV7M-PER_TARGET: "[[SYSROOT:[^"]+]]{{[/\\]+}}lib{{[/\\]+}}crt0.o"
 // CHECK-ARMV7M-PER-TARGET: "-L[[SYSROOT:[^"]+]]{{[/\\]+}}lib"
 // CHECK-ARMV7M-PER-TARGET: "-L[[RESOURCE_DIR:[^"]+]]{{[/\\]+}}lib{{[/\\]+}}armv7m-vendor-none-eabi
 // CHECK-ARMV7M-PER-TARGET: "-lc" "-lm" "{{[^"]*}}libclang_rt.builtins.a"
@@ -56,6 +59,7 @@
 // RUN:     --sysroot=%S/Inputs/baremetal_arm | FileCheck --check-prefix=CHECK-V6M-DEFAULTCXX %s
 // CHECK-V6M-DEFAULTCXX: "-resource-dir" "[[RESOURCE_DIR:[^"]+]]"
 // CHECK-V6M-DEFAULTCXX: ld{{(.exe)?}}" "{{.*}}.o" "-Bstatic" "-EL"
+// CHECK-V6M-DEFAULTCXX-SAME: "[[SYSROOT:[^"]+]]{{[/\\]+}}lib{{[/\\]+}}crt0.o"
 // CHECK-V6M-DEFAULTCXX-SAME: "-L{{[^"]*}}{{[/\\]+}}Inputs{{[/\\]+}}baremetal_arm{{[/\\]+}}lib"
 // CHECK-V6M-DEFAULTCXX-SAME: "-lc++" "-lc++abi" "-lunwind"
 // CHECK-V6M-DEFAULTCXX-SAME: "-lc" "-lm" "{{[^"]*}}libclang_rt.builtins.a" "--target2=rel" "-o" "a.out"
@@ -117,6 +121,10 @@
 // RUN:   | FileCheck %s --check-prefix=CHECK-THREAD-MODEL-POSIX
 // CHECK-THREAD-MODEL-POSIX: Thread model: posix
 
+// RUN: %clangxx -### --target=arm-none-eabi -nostartfiles -v %s 2>&1 \
+// RUN:   | FileCheck %s --check-prefix=CHECK-NOSTARTFILES
+// CHECK-NOSTARTFILES-NOT: "crt0.o"
+
 // RUN: %clang -### --target=arm-none-eabi -rtlib=libgcc -v %s 2>&1 \
 // RUN:   | FileCheck %s --check-prefix=CHECK-RTLIB-GCC
 // CHECK-RTLIB-GCC: -lgcc