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

[MaskRay]

Summary

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.

[MaskRay]

add a test

[MaskRay]

Ping

[sylvestre.ledru]

Maybe add it to the release notes too?

[MaskRay]

Add a release note

[thesamesam]

This is working well here on Gentoo.

This brings some long-desired feature parity to Clang which we've been wanting downstream: GCC has had this option for quite a few years (after pushing from various downstreams, including us) and this ends up biting folks who want to try migrate to Clang as their system compiler.

The change is rather conservative given we're defaulting to PIE being off for now (and this is the same as GCC anyway).

[MaskRay]

I will wait until Dec 14 before committing.

Hope Arch Linux folks can test this, too: @felixonmars @foutrelis

[foutrelis]

No issues with default PIE and SSP on Arch for over 4 years now. It's nice to see this being upstreamed; thanks for doing it. This patch worked fine.

Based on my own hack of a patch, the tests should be somewhat straight-foward to fix, though I'm not sure how elegantly they can be adjusted.

[joerg]

clang/CMakeLists.txt

230

This option should really be called something like CLANG_DEFAULT_PIE_ON_LINUX or so. It should be explicit from the name that it only effects that toolchain and not all the various toolchains that support PIE.

[MaskRay]

clang/CMakeLists.txt

230

This name is fine with me. This ecosystem variety probably only happens for Linux and other operations systems probably can just switch unconditionally (with possibly gated on an os version).

[MaskRay]

CLANG_DEFAULT_PIE => CLANG_DEFAULT_PIE_ON_LINUX

I have fixed all test/Driver tests in a separate commit.

[joerg]

Last update introduced a lot of unrelated changes? But the actual intended change seems fine now.

[MaskRay]

In D113372#3188178, @joerg wrote:

Last update introduced a lot of unrelated changes? But the actual intended change seems fine now.

The last update just did a renaming. I have checked that changes are all intended.

[MaskRay]

Rename test/Driver/default-pie.c to linux-default-pie.c

clang-format a region.

[arichardson]

clang/CMakeLists.txt

232

Can these 3 lines be removed after D115751?

[MaskRay]

clang/CMakeLists.txt

232

Thx. Removed in b5d3bbcc9433193351a22b738c7ff4b007cb1e68

[mgorny]

When enabled, this seems to break a fair number of tests:

Clang :: CodeGen/mips-vector-return.c
Clang :: Driver/hexagon-toolchain-elf.c
Clang :: Driver/hip-fpie-option.hip
Clang :: Driver/mips-cs.cpp
Clang :: Driver/mips-fsf.cpp
Clang :: Driver/mips-img-v2.cpp
Clang :: Driver/mips-img.cpp
Clang :: Driver/mips-mti-linux.c

I've been able to get the hexagon test to work by passing -fno-pie explicitly but others don't seem this easy.

[MaskRay]

In D113372#3316751, @mgorny wrote:

When enabled, this seems to break a fair number of tests:

Clang :: CodeGen/mips-vector-return.c
Clang :: Driver/hexagon-toolchain-elf.c
Clang :: Driver/hip-fpie-option.hip
Clang :: Driver/mips-cs.cpp
Clang :: Driver/mips-fsf.cpp
Clang :: Driver/mips-img-v2.cpp
Clang :: Driver/mips-img.cpp
Clang :: Driver/mips-mti-linux.c

I've been able to get the hexagon test to work by passing -fno-pie explicitly but others don't seem this easy.

In release/14.x, these have all been fixed.

clang/CMakeLists.txt

 set(ENABLE_LINKER_BUILD_ID OFF CACHE BOOL "pass --build-id to ld")
 
 set(ENABLE_X86_RELAX_RELOCATIONS ON CACHE BOOL
     "enable x86 relax relocations by default")
 
 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)")
 set(CLANG_DEFAULT_STD_CXX "" CACHE STRING
   "Default standard to use for C++/ObjC++ code (IDENT from LangStandards.def, empty for platform default)")
 
 set(CLANG_DEFAULT_LINKER "" CACHE STRING
   "Default linker to use (linker name or absolute path, empty for platform default)")

clang/docs/ReleaseNotes.rst

 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
 ------------
 
 - ``TypeLoc`` AST Matchers are now available. These matchers provide helpful
   utilities for matching ``TypeLoc`` nodes, such as the ``pointerTypeLoc``
   matcher or the ``hasReturnTypeLoc`` matcher. The addition of these matchers
   was made possible by changes to the handling of ``TypeLoc`` nodes that

clang/include/clang/Config/config.h.cmake

 /* This generated file is for internal use. Do not include it from headers. */
 
 #ifdef CLANG_CONFIG_H
 #error config.h can only be included once
 #else
 #define CLANG_CONFIG_H
 
 /* 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}"
 
 /* Default C/ObjC standard to use. */
 #cmakedefine CLANG_DEFAULT_STD_C LangStandard::lang_${CLANG_DEFAULT_STD_C}
 
 /* Default C++/ObjC++ standard to use. */
 #cmakedefine CLANG_DEFAULT_STD_CXX LangStandard::lang_${CLANG_DEFAULT_STD_CXX}

clang/lib/Driver/ToolChains/Linux.cpp

if (GCCInstallation.isValid()) {
     CC1Args.push_back("-isystem");
     CC1Args.push_back(DriverArgs.MakeArgString(
         GCCInstallation.getParentLibPath() + "/../" +
         GCCInstallation.getTriple().str() + "/include"));
   }
 }
 
 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 {
   // Outline atomics for AArch64 are supported by compiler-rt
   // and libgcc since 9.3.1
   assert(getTriple().isAArch64() && "expected AArch64 target!");
   ToolChain::RuntimeLibType RtLib = GetRuntimeLibType(Args);
   if (RtLib == ToolChain::RLT_CompilerRT)

clang/test/Driver/fsanitize.c

+// 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
 // RUN: %clang -target x86_64-linux-gnu -fsanitize=undefined-trap -fsanitize-undefined-trap-on-error %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-UNDEFINED-TRAP
 // RUN: %clang -target x86_64-linux-gnu -fsanitize-undefined-trap-on-error -fsanitize=undefined-trap %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-UNDEFINED-TRAP
 // RUN: %clang -target x86_64-linux-gnu -fsanitize-trap -fsanitize=undefined-trap %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-UNDEFINED-TRAP
 // CHECK-UNDEFINED-TRAP-NOT: -fsanitize-recover
 // CHECK-UNDEFINED-TRAP: "-fsanitize={{((signed-integer-overflow|integer-divide-by-zero|shift-base|shift-exponent|unreachable|return|vla-bound|alignment|null|pointer-overflow|float-cast-overflow|array-bounds|enum|bool|builtin|returns-nonnull-attribute|nonnull-attribute|function),?){18}"}}

clang/test/Driver/linux-default-pie.c

+// 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"

clang/test/Driver/linux-ld.c

-// 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.
 //
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
 // RUN:     --target=i386-unknown-linux -rtlib=platform \
 // RUN:     --gcc-toolchain="" \
 // RUN:     --sysroot=%S/Inputs/basic_linux_tree \
 // RUN:   | FileCheck --check-prefix=CHECK-LD-32 %s

clang/test/lit.cfg.py

 config.substitutions.append(('%host_cc', config.host_cc))
 config.substitutions.append(('%host_cxx', config.host_cxx))
 
 
 # Plugins (loadable modules)
 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 != '':
     config.available_features.add('default-cxx-stdlib-set')
 
 # As of 2011.08, crash-recovery tests still do not pass on FreeBSD.
 if platform.system() not in ['FreeBSD']:
     config.available_features.add('crash-recovery')

clang/test/lit.site.cfg.py.in

 config.clang_lib_dir = path(r"@CMAKE_LIBRARY_OUTPUT_DIRECTORY@")
 config.host_triple = "@LLVM_HOST_TRIPLE@"
 config.target_triple = "@TARGET_TRIPLE@"
 config.host_cc = "@CMAKE_C_COMPILER@"
 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@"
 config.clang_examples = @CLANG_BUILD_EXAMPLES@
 config.enable_shared = @ENABLE_SHARED@
 config.enable_backtrace = @ENABLE_BACKTRACES@
 config.enable_experimental_new_pass_manager = @LLVM_ENABLE_NEW_PASS_MANAGER@
 config.enable_threads = @LLVM_ENABLE_THREADS@

llvm/utils/gn/secondary/clang/include/clang/Config/BUILD.gn

 import("//clang/lib/ARCMigrate/enable.gni")
 import("//clang/lib/StaticAnalyzer/Frontend/enable.gni")
 import("//llvm/utils/gn/build/libs/xml/enable.gni")
 import("//llvm/utils/gn/build/write_cmake_config.gni")
 import("//llvm/version.gni")
 
 write_cmake_config("Config") {
   input = "config.h.cmake"
   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=",
     "CLANG_DEFAULT_CXX_STDLIB=",
     "CLANG_DEFAULT_RTLIB=",
     "CLANG_DEFAULT_OBJCOPY=objcopy",
     "CLANG_DEFAULT_OPENMP_RUNTIME=libomp",
     "CLANG_DEFAULT_UNWINDLIB=",

utils/bazel/llvm-project-overlay/clang/include/clang/Config/config.h

 #ifdef CLANG_CONFIG_H
 #error config.h can only be included once
 #else
 #define CLANG_CONFIG_H
 
 /* 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 ""
 
 /* Default C/ObjC standard to use. */
 /* #undef CLANG_DEFAULT_STD_C */
 
 /* Default C++/ObjC++ standard to use. */
 /* #undef CLANG_DEFAULT_STD_CXX */