Frederik Harwath 50a3368f22
[Clang] Take libstdc++ into account during GCC detection (#145056)
The Generic_GCC::GCCInstallationDetector class picks the GCC
installation directory with the largest version number. Since the
location of the libstdc++ include directories is tied to the GCC
version, this can break C++ compilation if the libstdc++ headers for
this particular GCC version are not available. Linux distributions tend
to package the libstdc++ headers separately from GCC. This frequently
leads to situations in which a newer version of GCC gets installed as a
dependency of another package without installing the corresponding
libstdc++ package. Clang then fails to compile C++ code because it
cannot find the libstdc++ headers. Since libstdc++ headers are in fact
installed on the system, the GCC installation continues to work, the
user may not be aware of the details of the GCC detection, and the
compiler does not recognize the situation and emit a warning, this
behavior can be hard to understand - as witnessed by many related bug
reports over the years.

The goal of this work is to change the GCC detection to prefer GCC
installations that contain libstdc++ include directories over those
which do not. This should happen regardless of the input language since
picking different GCC installations for a build that mixes C and C++
might lead to incompatibilities.
Any change to the GCC installation detection will probably have a
negative impact on some users. For instance, for a C user who relies on
using the GCC installation with the largest version number, it might
become necessary to use the --gcc-install-dir option to ensure that this
GCC version is selected.
This seems like an acceptable trade-off given that the situation for
users who do not have any special demands on the particular GCC
installation directory would be improved significantly.
 
This patch does not yet change the automatic GCC installation directory
choice. Instead, it does introduce a warning that informs the user about
the future change if the chosen GCC installation directory differs from
the one that would be chosen if the libstdc++ headers are taken into
account.

See also this related Discourse discussion:
https://discourse.llvm.org/t/rfc-take-libstdc-into-account-during-gcc-detection/86992.
2025-08-19 16:55:45 +02:00

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7.6 KiB
C++

//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include "Managarm.h"
#include "Arch/RISCV.h"
#include "clang/Config/config.h"
#include "clang/Driver/CommonArgs.h"
#include "clang/Driver/Driver.h"
#include "clang/Driver/Options.h"
#include "clang/Driver/SanitizerArgs.h"
#include "llvm/Option/ArgList.h"
#include "llvm/Support/Path.h"
using namespace clang::driver;
using namespace clang::driver::toolchains;
using namespace clang;
using namespace llvm::opt;
using tools::addPathIfExists;
std::string Managarm::getMultiarchTriple(const Driver &D,
const llvm::Triple &TargetTriple,
StringRef SysRoot) const {
switch (TargetTriple.getArch()) {
default:
return TargetTriple.str();
case llvm::Triple::x86_64:
return "x86_64-managarm-" + TargetTriple.getEnvironmentName().str();
case llvm::Triple::aarch64:
return "aarch64-managarm-" + TargetTriple.getEnvironmentName().str();
case llvm::Triple::riscv64:
return "riscv64-managarm-" + TargetTriple.getEnvironmentName().str();
}
}
static StringRef getOSLibDir(const llvm::Triple &Triple, const ArgList &Args) {
// It happens that only x86, PPC and SPARC use the 'lib32' variant of
// oslibdir, and using that variant while targeting other architectures causes
// problems because the libraries are laid out in shared system roots that
// can't cope with a 'lib32' library search path being considered. So we only
// enable them when we know we may need it.
//
// FIXME: This is a bit of a hack. We should really unify this code for
// reasoning about oslibdir spellings with the lib dir spellings in the
// GCCInstallationDetector, but that is a more significant refactoring.
if (Triple.getArch() == llvm::Triple::x86 || Triple.isPPC32() ||
Triple.getArch() == llvm::Triple::sparc)
return "lib32";
if (Triple.getArch() == llvm::Triple::x86_64 && Triple.isX32())
return "libx32";
if (Triple.getArch() == llvm::Triple::riscv32)
return "lib32";
return Triple.isArch32Bit() ? "lib" : "lib64";
}
Managarm::Managarm(const Driver &D, const llvm::Triple &Triple,
const ArgList &Args)
: Generic_ELF(D, Triple, Args) {
GCCInstallation.init(Triple, Args);
Multilibs = GCCInstallation.getMultilibs();
SelectedMultilibs.assign({GCCInstallation.getMultilib()});
std::string SysRoot = computeSysRoot();
ToolChain::path_list &PPaths = getProgramPaths();
Generic_GCC::PushPPaths(PPaths);
#ifdef ENABLE_LINKER_BUILD_ID
ExtraOpts.push_back("--build-id");
#endif
// The selection of paths to try here is designed to match the patterns which
// the GCC driver itself uses, as this is part of the GCC-compatible driver.
// This was determined by running GCC in a fake filesystem, creating all
// possible permutations of these directories, and seeing which ones it added
// to the link paths.
path_list &Paths = getFilePaths();
const std::string OSLibDir = std::string(getOSLibDir(Triple, Args));
const std::string MultiarchTriple = getMultiarchTriple(D, Triple, SysRoot);
Generic_GCC::AddMultilibPaths(D, SysRoot, OSLibDir, MultiarchTriple, Paths);
addPathIfExists(D, concat(SysRoot, "/lib", MultiarchTriple), Paths);
addPathIfExists(D, concat(SysRoot, "/lib/..", OSLibDir), Paths);
addPathIfExists(D, concat(SysRoot, "/usr/lib", MultiarchTriple), Paths);
addPathIfExists(D, concat(SysRoot, "/usr", OSLibDir), Paths);
Generic_GCC::AddMultiarchPaths(D, SysRoot, OSLibDir, Paths);
addPathIfExists(D, concat(SysRoot, "/lib"), Paths);
addPathIfExists(D, concat(SysRoot, "/usr/lib"), Paths);
}
bool Managarm::HasNativeLLVMSupport() const { return true; }
Tool *Managarm::buildLinker() const {
return new tools::gnutools::Linker(*this);
}
Tool *Managarm::buildAssembler() const {
return new tools::gnutools::Assembler(*this);
}
std::string Managarm::computeSysRoot() const {
if (!getDriver().SysRoot.empty())
return getDriver().SysRoot;
return std::string();
}
std::string Managarm::getDynamicLinker(const ArgList &Args) const {
switch (getTriple().getArch()) {
case llvm::Triple::aarch64:
return "/lib/aarch64-managarm/ld.so";
case llvm::Triple::riscv64: {
StringRef ABIName = tools::riscv::getRISCVABI(Args, getTriple());
return ("/lib/riscv64-managarm/ld-riscv64-" + ABIName + ".so").str();
}
case llvm::Triple::x86_64:
return "/lib/x86_64-managarm/ld.so";
default:
llvm_unreachable("unsupported architecture");
}
}
void Managarm::AddClangSystemIncludeArgs(const ArgList &DriverArgs,
ArgStringList &CC1Args) const {
const Driver &D = getDriver();
std::string SysRoot = computeSysRoot();
if (DriverArgs.hasArg(clang::driver::options::OPT_nostdinc))
return;
if (!DriverArgs.hasArg(options::OPT_nostdlibinc))
addSystemInclude(DriverArgs, CC1Args, SysRoot + "/usr/local/include");
// Add 'include' in the resource directory, which is similar to
// GCC_INCLUDE_DIR (private headers) in GCC.
if (!DriverArgs.hasArg(options::OPT_nobuiltininc)) {
SmallString<128> ResourceDirInclude(D.ResourceDir);
llvm::sys::path::append(ResourceDirInclude, "include");
addSystemInclude(DriverArgs, CC1Args, ResourceDirInclude);
}
if (DriverArgs.hasArg(options::OPT_nostdlibinc))
return;
// TOOL_INCLUDE_DIR
AddMultilibIncludeArgs(DriverArgs, CC1Args);
// Check for configure-time C include directories.
StringRef CIncludeDirs(C_INCLUDE_DIRS);
if (CIncludeDirs != "") {
SmallVector<StringRef, 5> dirs;
CIncludeDirs.split(dirs, ":");
for (StringRef dir : dirs) {
StringRef Prefix =
llvm::sys::path::is_absolute(dir) ? StringRef(SysRoot) : "";
addExternCSystemInclude(DriverArgs, CC1Args, Prefix + dir);
}
return;
}
// On systems using multiarch, add /usr/include/$triple before
// /usr/include.
std::string MultiarchIncludeDir = getMultiarchTriple(D, getTriple(), SysRoot);
if (!MultiarchIncludeDir.empty())
addExternCSystemInclude(
DriverArgs, CC1Args,
concat(SysRoot, "/usr/include", MultiarchIncludeDir));
// Add an include of '/include' directly. This isn't provided by default by
// system GCCs, but is often used with cross-compiling GCCs, and harmless to
// add even when Clang is acting as-if it were a system compiler.
addExternCSystemInclude(DriverArgs, CC1Args, concat(SysRoot, "/include"));
addExternCSystemInclude(DriverArgs, CC1Args, concat(SysRoot, "/usr/include"));
}
void Managarm::addLibStdCxxIncludePaths(
const llvm::opt::ArgList &DriverArgs,
llvm::opt::ArgStringList &CC1Args) const {
// We need a detected GCC installation on Managarm to provide libstdc++'s
// headers.
if (!GCCInstallation.isValid())
return;
// Try generic GCC detection.
addGCCLibStdCxxIncludePaths(DriverArgs, CC1Args);
}
SanitizerMask Managarm::getSupportedSanitizers() const {
const bool IsX86_64 = getTriple().getArch() == llvm::Triple::x86_64;
SanitizerMask Res = ToolChain::getSupportedSanitizers();
Res |= SanitizerKind::PointerCompare;
Res |= SanitizerKind::PointerSubtract;
Res |= SanitizerKind::KernelAddress;
Res |= SanitizerKind::Vptr;
if (IsX86_64)
Res |= SanitizerKind::KernelMemory;
return Res;
}
void Managarm::addExtraOpts(llvm::opt::ArgStringList &CmdArgs) const {
for (const auto &Opt : ExtraOpts)
CmdArgs.push_back(Opt.c_str());
}