[clang] Add option for -nolibc in Driver/ToolChains/Baremetal.cpp

[saturn691]

Some tests in LLVM-libc require this flag (#145349), which requires compiler-rt to be linked in, but not the C library. With this change, the -nolibc flag will not be ignored.

Minor changes: clang-format

[llvmbot]

@llvm/pr-subscribers-clang

Author: William Huynh (saturn691)

Changes

Some tests in LLVM-libc require this flag, so compiler-rt is still linked in, but not the C library. With this change, it will not be ignored.

Minor changes: clang-format

---

Full diff: https://github.com/llvm/llvm-project/pull/145700.diff

1 Files Affected:

• (modified) clang/lib/Driver/ToolChains/BareMetal.cpp (+12-10)

diff --git a/clang/lib/Driver/ToolChains/BareMetal.cpp b/clang/lib/Driver/ToolChains/BareMetal.cpp
index d8168ed15febd..b87427110d7de 100644
--- a/clang/lib/Driver/ToolChains/BareMetal.cpp
+++ b/clang/lib/Driver/ToolChains/BareMetal.cpp
@@ -339,15 +339,15 @@ void BareMetal::AddClangCXXStdlibIncludeArgs(const ArgList &DriverArgs,
   };
 
   switch (GetCXXStdlibType(DriverArgs)) {
-    case ToolChain::CST_Libcxx: {
-      SmallString<128> P(D.Dir);
-      llvm::sys::path::append(P, "..", "include");
-      AddCXXIncludePath(P);
-      break;
-    }
-    case ToolChain::CST_Libstdcxx:
-      // We only support libc++ toolchain installation.
-      break;
+  case ToolChain::CST_Libcxx: {
+    SmallString<128> P(D.Dir);
+    llvm::sys::path::append(P, "..", "include");
+    AddCXXIncludePath(P);
+    break;
+  }
+  case ToolChain::CST_Libstdcxx:
+    // We only support libc++ toolchain installation.
+    break;
   }
 
   std::string SysRoot(computeSysRoot());
@@ -498,7 +498,9 @@ void baremetal::Linker::ConstructJob(Compilation &C, const JobAction &JA,
   if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nodefaultlibs)) {
     AddRunTimeLibs(TC, D, CmdArgs, Args);
 
-    CmdArgs.push_back("-lc");
+    if (!Args.hasArg(options::OPT_nolibc)) {
+      CmdArgs.push_back("-lc");
+    }
   }
 
   if (D.isUsingLTO())

[llvmbot]

@llvm/pr-subscribers-clang-driver

Author: William Huynh (saturn691)

Changes

Some tests in LLVM-libc require this flag, so compiler-rt is still linked in, but not the C library. With this change, it will not be ignored.

Minor changes: clang-format

---

Full diff: https://github.com/llvm/llvm-project/pull/145700.diff

1 Files Affected:

• (modified) clang/lib/Driver/ToolChains/BareMetal.cpp (+12-10)

diff --git a/clang/lib/Driver/ToolChains/BareMetal.cpp b/clang/lib/Driver/ToolChains/BareMetal.cpp
index d8168ed15febd..b87427110d7de 100644
--- a/clang/lib/Driver/ToolChains/BareMetal.cpp
+++ b/clang/lib/Driver/ToolChains/BareMetal.cpp
@@ -339,15 +339,15 @@ void BareMetal::AddClangCXXStdlibIncludeArgs(const ArgList &DriverArgs,
   };
 
   switch (GetCXXStdlibType(DriverArgs)) {
-    case ToolChain::CST_Libcxx: {
-      SmallString<128> P(D.Dir);
-      llvm::sys::path::append(P, "..", "include");
-      AddCXXIncludePath(P);
-      break;
-    }
-    case ToolChain::CST_Libstdcxx:
-      // We only support libc++ toolchain installation.
-      break;
+  case ToolChain::CST_Libcxx: {
+    SmallString<128> P(D.Dir);
+    llvm::sys::path::append(P, "..", "include");
+    AddCXXIncludePath(P);
+    break;
+  }
+  case ToolChain::CST_Libstdcxx:
+    // We only support libc++ toolchain installation.
+    break;
   }
 
   std::string SysRoot(computeSysRoot());
@@ -498,7 +498,9 @@ void baremetal::Linker::ConstructJob(Compilation &C, const JobAction &JA,
   if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nodefaultlibs)) {
     AddRunTimeLibs(TC, D, CmdArgs, Args);
 
-    CmdArgs.push_back("-lc");
+    if (!Args.hasArg(options::OPT_nolibc)) {
+      CmdArgs.push_back("-lc");
+    }
   }
 
   if (D.isUsingLTO())

[vhscampos]

The change LGTM. Please just fix a typo in the PR description: "requre"

[petrhosek]

The runtime library is not relevant to this test so I'd omit this line.

Suggested change

// CHECK-NOLIBC: "{{[^"]*}}libclang_rt.builtins.a"

[saturn691]

The thing I'm trying to test is the follows, I think it still makes sense to test libclang_rt.builtings.a (replace libgcc with compiler-rt):

-nolibc
Do not use the C library or system libraries tightly coupled with it when linking. Still link with the startup files, libgcc or toolchain provided language support libraries such as libgnat, libgfortran or libstdc++ unless options preventing their inclusion are used as well.

-nostdlib
Do not use the standard system startup files or libraries when linking. No startup files and only the libraries you specify are passed to the linker, and options specifying linkage of the system libraries, such as -static-libgcc or -shared-libgcc, are ignored.

The compiler may generate calls to memcmp, memset, memcpy and memmove. These entries are usually resolved by entries in libc. These entry points should be supplied through some other mechanism when this option is specified.

One of the standard libraries bypassed by -nostdlib and -nodefaultlibs is libgcc.a, a library of internal subroutines which GCC uses to overcome shortcomings of particular machines, or special needs for some languages.

Reference: https://gcc.gnu.org/onlinedocs/gcc/Link-Options.html#index-nolibc

[petrhosek]

Ditto here.

Suggested change

// CHECK-NOSTDLIB-NOT: "{{[^"]*}}libclang_rt.builtins.a"

[saturn691]

Ditto previous comment