[Driver] Add CLANG_DEFAULT_PIE_ON_LINUX to emulate GCC --enable-default-pie

In 2015-05, GCC added the configure option `--enable-default-pie`. When enabled,

* in the absence of -fno-pic/-fpie/-fpic (and their upper-case variants), -fPIE is the default.
* in the absence of -no-pie/-pie/-shared/-static/-static-pie, -pie is the default.

This has been adopted by all(?) major distros.

I think default PIE is the majority in the Linux world, but
--disable-default-pie users is not that uncommon because GCC upstream hasn't
switched the default yet (https://gcc.gnu.org/PR103398).

This patch add CLANG_DEFAULT_PIE_ON_LINUX which allows distros to use default PIE.
The option is justified as its adoption can be very high among Linux distros
to make Clang default match GCC, and is likely a future-new-default, at which
point we will remove CLANG_DEFAULT_PIE_ON_LINUX.
The lit feature `default-pie-on-linux` can be handy to exclude default PIE sensitive tests.

Reviewed By: foutrelis, sylvestre.ledru, thesamesam

Differential Revision: https://reviews.llvm.org/D113372

11 files changed, 31 insertions, 4 deletions

diff --git a/clang/CMakeLists.txt b/clang/CMakeLists.txt
index 6f26e94f3160..00243d8b13b9 100644
--- a/clang/CMakeLists.txt
+++ b/clang/CMakeLists.txt
@@ -227,6 +227,11 @@ set(ENABLE_X86_RELAX_RELOCATIONS ON CACHE BOOL
 set(CLANG_SPAWN_CC1 OFF CACHE BOOL
     "Whether clang should use a new process for the CC1 invocation")
 
+option(CLANG_DEFAULT_PIE_ON_LINUX "Default to -fPIE and -pie on Linux" OFF)
+if(CLANG_DEFAULT_PIE_ON_LINUX)
+  set(CLANG_DEFAULT_PIE_ON_LINUX 1)
+endif()
+
 # TODO: verify the values against LangStandards.def?
 set(CLANG_DEFAULT_STD_C "" CACHE STRING
   "Default standard to use for C/ObjC code (IDENT from LangStandards.def, empty for platform default)")
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 6b0ce5bfd595..07953a8fb0fd 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -249,7 +249,10 @@ Internal API Changes
 Build System Changes
 --------------------
 
-- ...
+- Linux distros can specify ``-DCLANG_DEFAULT_PIE_ON_LINUX=On`` to use ``-fPIE`` and
+  ``-pie`` by default. This matches GCC installations on many Linux distros
+  (configured with ``--enable-default-pie``).
+  (`D113372 <https://reviews.llvm.org/D113372>`_)
 
 AST Matchers
 ------------
diff --git a/clang/include/clang/Config/config.h.cmake b/clang/include/clang/Config/config.h.cmake
index a240862c5289..53386ef94129 100644
--- a/clang/include/clang/Config/config.h.cmake
+++ b/clang/include/clang/Config/config.h.cmake
@@ -8,6 +8,9 @@
 /* Bug report URL. */
 #define BUG_REPORT_URL "${BUG_REPORT_URL}"
 
+/* Default to -fPIE and -pie on Linux. */
+#cmakedefine01 CLANG_DEFAULT_PIE_ON_LINUX
+
 /* Default linker to use. */
 #define CLANG_DEFAULT_LINKER "${CLANG_DEFAULT_LINKER}"
 
diff --git a/clang/lib/Driver/ToolChains/Linux.cpp b/clang/lib/Driver/ToolChains/Linux.cpp
index 7494c2129211..e413640abad3 100644
--- a/clang/lib/Driver/ToolChains/Linux.cpp
+++ b/clang/lib/Driver/ToolChains/Linux.cpp
@@ -663,8 +663,8 @@ void Linux::AddIAMCUIncludeArgs(const ArgList &DriverArgs,
 }
 
 bool Linux::isPIEDefault(const llvm::opt::ArgList &Args) const {
-  return getTriple().isAndroid() || getTriple().isMusl() ||
-         getSanitizerArgs(Args).requiresPIE();
+  return CLANG_DEFAULT_PIE_ON_LINUX || getTriple().isAndroid() ||
+         getTriple().isMusl() || getSanitizerArgs(Args).requiresPIE();
 }
 
 bool Linux::IsAArch64OutlineAtomicsDefault(const ArgList &Args) const {
diff --git a/clang/test/Driver/fsanitize.c b/clang/test/Driver/fsanitize.c
index a6b5776c9e70..7bcda5c33dc9 100644
--- a/clang/test/Driver/fsanitize.c
+++ b/clang/test/Driver/fsanitize.c
@@ -1,3 +1,4 @@
+// UNSUPPORTED: default-pie-on-linux
 // RUN: %clang -target x86_64-linux-gnu -fsanitize=undefined -fsanitize-trap=undefined %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-UNDEFINED-TRAP
 // RUN: %clang -target x86_64-linux-gnu -fsanitize=undefined -fsanitize-trap=undefined -fno-sanitize-trap=signed-integer-overflow %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-UNDEFINED-TRAP2
 // RUN: %clang -target x86_64-linux-gnu -fsanitize=undefined -fsanitize-undefined-trap-on-error %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-UNDEFINED-TRAP
diff --git a/clang/test/Driver/linux-default-pie.c b/clang/test/Driver/linux-default-pie.c
new file mode 100644
index 000000000000..6772a6cd3fd0
--- /dev/null
+++ b/clang/test/Driver/linux-default-pie.c
@@ -0,0 +1,7 @@
+// REQUIRES: default-pie-on-linux
+/// Test -DCLANG_DEFAULT_PIE_ON_LINUX=on.
+
+// RUN: %clang -### --target=aarch64-linux-gnu %s 2>&1 | FileCheck %s --check-prefix=PIE2
+
+// PIE2: "-mrelocation-model" "pic" "-pic-level" "2" "-pic-is-pie"
+// PIE2: "-pie"
diff --git a/clang/test/Driver/linux-ld.c b/clang/test/Driver/linux-ld.c
index 31905e1a3d00..b70b712c2eb7 100644
--- a/clang/test/Driver/linux-ld.c
+++ b/clang/test/Driver/linux-ld.c
@@ -1,4 +1,4 @@
-// UNSUPPORTED: system-windows
+// UNSUPPORTED: system-windows, default-pie-on-linux
 // General tests that ld invocations on Linux targets sane. Note that we use
 // sysroot to make these tests independent of the host system.
 //
diff --git a/clang/test/lit.cfg.py b/clang/test/lit.cfg.py
index 5a9a1abf4531..514ddf997c7c 100644
--- a/clang/test/lit.cfg.py
+++ b/clang/test/lit.cfg.py
@@ -121,6 +121,9 @@ config.substitutions.append(('%host_cxx', config.host_cxx))
 if config.has_plugins and config.llvm_plugin_ext:
     config.available_features.add('plugins')
 
+if config.clang_default_pie_on_linux == '1':
+    config.available_features.add('default-pie-on-linux')
+
 # Set available features we allow tests to conditionalize on.
 #
 if config.clang_default_cxx_stdlib != '':
diff --git a/clang/test/lit.site.cfg.py.in b/clang/test/lit.site.cfg.py.in
index a99550c3f909..807c1d347217 100644
--- a/clang/test/lit.site.cfg.py.in
+++ b/clang/test/lit.site.cfg.py.in
@@ -22,6 +22,7 @@ config.host_cxx = "@CMAKE_CXX_COMPILER@"
 config.llvm_use_sanitizer = "@LLVM_USE_SANITIZER@"
 config.have_zlib = @LLVM_ENABLE_ZLIB@
 config.clang_arcmt = @CLANG_ENABLE_ARCMT@
+config.clang_default_pie_on_linux = "@CLANG_DEFAULT_PIE_ON_LINUX@"
 config.clang_default_cxx_stdlib = "@CLANG_DEFAULT_CXX_STDLIB@"
 config.clang_staticanalyzer = @CLANG_ENABLE_STATIC_ANALYZER@
 config.clang_staticanalyzer_z3 = "@LLVM_WITH_Z3@"
diff --git a/llvm/utils/gn/secondary/clang/include/clang/Config/BUILD.gn b/llvm/utils/gn/secondary/clang/include/clang/Config/BUILD.gn
index aa3e40af1d9d..f635c0abe04d 100644
--- a/llvm/utils/gn/secondary/clang/include/clang/Config/BUILD.gn
+++ b/llvm/utils/gn/secondary/clang/include/clang/Config/BUILD.gn
@@ -9,6 +9,7 @@ write_cmake_config("Config") {
   output = "$target_gen_dir/config.h"
   values = [
     "BUG_REPORT_URL=https://bugs.llvm.org/",
+    "CLANG_DEFAULT_PIE_ON_LINUX=0",
     "CLANG_DEFAULT_LINKER=",
     "CLANG_DEFAULT_STD_C=",
     "CLANG_DEFAULT_STD_CXX=",
diff --git a/utils/bazel/llvm-project-overlay/clang/include/clang/Config/config.h b/utils/bazel/llvm-project-overlay/clang/include/clang/Config/config.h
index 4d5cd0520a0c..ee4c6277d2ae 100644
--- a/utils/bazel/llvm-project-overlay/clang/include/clang/Config/config.h
+++ b/utils/bazel/llvm-project-overlay/clang/include/clang/Config/config.h
@@ -22,6 +22,9 @@
 /* Bug report URL. */
 #define BUG_REPORT_URL "https://bugs.llvm.org/"
 
+/* Default to -fPIE and -pie on Linux. */
+#define CLANG_DEFAULT_PIE_ON_LINUX 0
+
 /* Default linker to use. */
 #define CLANG_DEFAULT_LINKER ""