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[cling] Anchor the interpreter's clang driver on $ROOTSYS/bin #22754

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[cling] Anchor the interpreter's clang driver on $ROOTSYS/bin #22754

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17 changes: 17 additions & 0 deletions interpreter/cling/lib/Interpreter/CIFactory.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1428,6 +1428,23 @@ namespace {
#endif
// Add host specific includes, -resource-dir if necessary, and -isysroot
std::string ClingBin = GetExecutablePath(argv[0]);
#ifdef __linux__
// On Linux GetExecutablePath() resolves /proc/self/exe, i.e. the path of
// the *embedding* application rather than of ROOT/cling itself. clang's
// driver derives its installed-dir (and hence its GCC-installation and
// C-system-header sysroot detection) from this path. When libCore is loaded
// by an executable that does not live next to the ROOT installation, the
// sysroot is misdetected and the interpreter fails to find the C system
// headers (e.g. assert.h) even though they are present in the installation.
// Anchor the driver on $ROOTSYS/bin instead, mirroring how -resource-dir is
// already made ROOTSYS-relative below. LLVMDir is $ROOTSYS/etc/cling.
if (LLVMDir) {
llvm::SmallString<512> rootDriver(LLVMDir);
llvm::sys::path::append(rootDriver, "..", "..", "bin", "rootcling");

@ferdymercury ferdymercury Jul 3, 2026

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Does this also work with builtin_cling=OFF or builtin_llvm=OFF ?

@chrisburr chrisburr Jul 3, 2026

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Conda-forge is only using external clang/llvm. I had to leave before testing the build but I'll definitely test that case.

@chrisburr chrisburr Jul 3, 2026

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I've confirmed now that this works as expected.

llvm::sys::path::remove_dots(rootDriver, /*remove_dot_dot=*/true);
ClingBin.assign(rootDriver.data(), rootDriver.size());
}
#endif
AddHostArguments(ClingBin, argvCompile, LLVMDir, COpts);

// Be explicit about the stdlib on OS X
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