[PATCH] D97736: [Driver] Add a experimental option to link to LLVM libc.

[Siva Chandra via Phabricator via cfe-commits]

sivachandra created this revision.
sivachandra added a reviewer: phosek.
Herald added subscribers: jansvoboda11, dang.
sivachandra requested review of this revision.
Herald added a project: clang.
Herald added a subscriber: cfe-commits.

The experimental option is named -experimental-link-llvmlibc. Specifying
it will put -lllvmlibc before each system libc library component on the
link command line. This way, even if the user specifies -lm, functions
from LLVM libc will be picked instead of functions from the system libc
math library. Also, sanitizer and other options add -lm at few other
places. By putting -lllvmlibc right before each of them, we ensure that
functions available in LLVM libc are picked up by the linker.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D97736

Files:
  clang/include/clang/Driver/Options.td
  clang/lib/Driver/ToolChains/Gnu.cpp
  clang/test/Driver/linux-ld.c


Index: clang/test/Driver/linux-ld.c
===================================================================
--- clang/test/Driver/linux-ld.c
+++ clang/test/Driver/linux-ld.c
@@ -233,6 +233,26 @@
 // RUN:   | FileCheck --check-prefix=CHECK-CLANG-LD-STATIC-PIE-NOPIE %s
 // CHECK-CLANG-LD-STATIC-PIE-NOPIE: error: cannot specify 'nopie' along with 'static-pie'
 //
+// RUN: %clang -experimental-link-llvmlibc -no-canonical-prefixes %s -### -o %t.o 2>&1 \
+// RUN:     --target=x86_64-unknown-linux -rtlib=platform \
+// RUN:     --gcc-toolchain="" \
+// RUN:     --sysroot=%S/Inputs/basic_linux_tree \
+// RUN:   | FileCheck --check-prefix=CHECK-CLANG-LD-LINK-LLVMLIBC %s
+// CHECK-CLANG-LD-LINK-LLVMLIBC: "{{.*}}ld{{(.exe)?}}" "--sysroot=[[SYSROOT:[^"]+]]"
+// CHECK-CLANG-LD-LINK-LLVMLIBC: "-m" "elf_x86_64"
+// CHECK-CLANG-LD-LINK-LLVMLIBC: "-lllvmlibc" "-lc"
+//
+// RUN: %clang -experimental-link-llvmlibc -no-canonical-prefixes %s -### -o %t.o 2>&1 \
+// RUN:     --target=x86_64-unknown-linux -rtlib=platform \
+// RUN:     --gcc-toolchain="" \
+// RUN:     --sysroot=%S/Inputs/basic_linux_tree \
+// RUN:     -lm \
+// RUN:   | FileCheck --check-prefix=CHECK-CLANG-LD-LINK-LLVMLIBC-LM %s
+// CHECK-CLANG-LD-LINK-LLVMLIBC-LM: "{{.*}}ld{{(.exe)?}}" "--sysroot=[[SYSROOT:[^"]+]]"
+// CHECK-CLANG-LD-LINK-LLVMLIBC-LM: "-m" "elf_x86_64"
+// CHECK-CLANG-LD-LINK-LLVMLIBC-LM: "-lllvmlibc" "-lm"
+// CHECK-CLANG-LD-LINK-LLVMLIBC-LM: "-lllvmlibc" "-lc"
+//
 // RUN: %clang -dynamic -no-canonical-prefixes %s -### -o %t.o 2>&1 \
 // RUN:     --target=x86_64-unknown-linux -rtlib=platform \
 // RUN:     --gcc-toolchain="" \
Index: clang/lib/Driver/ToolChains/Gnu.cpp
===================================================================
--- clang/lib/Driver/ToolChains/Gnu.cpp
+++ clang/lib/Driver/ToolChains/Gnu.cpp
@@ -670,6 +670,25 @@
 
   Args.AddAllArgs(CmdArgs, options::OPT_T);
 
+  if (Args.hasArg(options::OPT_experimental_link_llvmlibc)) {
+    // We should add -lllvmlibc after all other link args have been accumulated.
+    // This way, we can iterate over all the link args and add -lllvmlibc before
+    // each libc library. This will also ensure that we prepend -lllvmlibc
+    // before any used listed -lm options.
+    ArgStringList WithLLVMLibc;
+    for (StringRef Arg : CmdArgs) {
+      if (Arg == "-lm" || Arg == "-lc") {
+        // TODO: Add -lllvmlibc before -lpthread when LLVM libc has pthread
+        // functions available.
+        WithLLVMLibc.push_back("-lllvmlibc");
+        WithLLVMLibc.push_back(Arg.data());
+      } else {
+        WithLLVMLibc.push_back(Arg.data());
+      }
+    }
+    CmdArgs = WithLLVMLibc;
+  }
+
   const char *Exec = Args.MakeArgString(ToolChain.GetLinkerPath());
   C.addCommand(std::make_unique<Command>(JA, *this,
                                          ResponseFileSupport::AtFileCurCP(),
Index: clang/include/clang/Driver/Options.td
===================================================================
--- clang/include/clang/Driver/Options.td
+++ clang/include/clang/Driver/Options.td
@@ -3623,6 +3623,7 @@
 def single__module : Flag<["-"], "single_module">;
 def specs_EQ : Joined<["-", "--"], "specs=">, Group<Link_Group>;
 def specs : Separate<["-", "--"], "specs">, Flags<[Unsupported]>;
+def experimental_link_llvmlibc : Flag<["-"], "experimental-link-llvmlibc">;
 def static_libgcc : Flag<["-"], "static-libgcc">;
 def static_libstdcxx : Flag<["-"], "static-libstdc++">;
 def static : Flag<["-", "--"], "static">, Group<Link_Group>, Flags<[NoArgumentUnused]>;


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