/**
 * Written in the D programming language.
 * This module provides ELF-specific support for sections with shared libraries.
 *
 * Copyright: Copyright Martin Nowak 2012-2013.
 * License:   $(HTTP www.boost.org/LICENSE_1_0.txt, Boost License 1.0).
 * Authors:   Martin Nowak
 * Source: $(DRUNTIMESRC rt/_sections_elf_shared.d)
 */

module rt.sections_elf_shared;

version (CRuntime_Glibc) enum SharedELF = true;
else version (CRuntime_Musl) enum SharedELF = true;
else version (FreeBSD) enum SharedELF = true;
else version (NetBSD) enum SharedELF = true;
else version (DragonFlyBSD) enum SharedELF = true;
else version (CRuntime_Bionic) enum SharedELF = true;
else version (CRuntime_UClibc) enum SharedELF = true;
else enum SharedELF = false;
static if (SharedELF):

// debug = PRINTF;

version (MIPS32)  version = MIPS_Any;
version (MIPS64)  version = MIPS_Any;
version (RISCV32) version = RISCV_Any;
version (RISCV64) version = RISCV_Any;

import core.internal.container.array;
import core.internal.container.hashtab;
import core.internal.elf.dl;
import core.memory;
import core.stdc.config : c_ulong;
import core.stdc.stdlib : calloc, free;
import core.sys.posix.pthread : pthread_mutex_destroy, pthread_mutex_init, pthread_mutex_lock, pthread_mutex_unlock;
import core.sys.posix.sys.types : pthread_mutex_t;
import rt.deh;
import rt.dmain2;
import rt.minfo;
import rt.util.utility : safeAssert;

version (linux)
{
    import core.sys.linux.dlfcn : Dl_info, dladdr, dlclose, dlinfo, dlopen, RTLD_DI_LINKMAP, RTLD_LAZY, RTLD_NOLOAD;
    import core.sys.linux.elf : DT_AUXILIARY, DT_FILTER, DT_NEEDED, DT_STRTAB, PF_W, PF_X, PT_DYNAMIC, PT_LOAD, PT_TLS;
    import core.sys.linux.link : ElfW, link_map;
}
else version (FreeBSD)
{
    import core.sys.freebsd.dlfcn : Dl_info, dladdr, dlclose, dlinfo, dlopen, RTLD_DI_LINKMAP, RTLD_LAZY, RTLD_NOLOAD;
    import core.sys.freebsd.sys.elf : DT_AUXILIARY, DT_FILTER, DT_NEEDED, DT_STRTAB, PF_W, PF_X, PT_DYNAMIC, PT_LOAD, PT_TLS;
    import core.sys.freebsd.sys.link_elf : ElfW, link_map;
}
else version (NetBSD)
{
    import core.sys.netbsd.dlfcn : Dl_info, dladdr, dlclose, dlinfo, dlopen, RTLD_DI_LINKMAP, RTLD_LAZY, RTLD_NOLOAD;
    import core.sys.netbsd.sys.elf : DT_AUXILIARY, DT_FILTER, DT_NEEDED, DT_STRTAB, PF_W, PF_X, PT_DYNAMIC, PT_LOAD, PT_TLS;
    import core.sys.netbsd.sys.link_elf : ElfW, link_map;
}
else version (DragonFlyBSD)
{
    import core.sys.dragonflybsd.dlfcn : Dl_info, dladdr, dlclose, dlinfo, dlopen, RTLD_DI_LINKMAP, RTLD_LAZY, RTLD_NOLOAD;
    import core.sys.dragonflybsd.sys.elf : DT_AUXILIARY, DT_FILTER, DT_NEEDED, DT_STRTAB, PF_W, PF_X, PT_DYNAMIC, PT_LOAD, PT_TLS;
    import core.sys.dragonflybsd.sys.link_elf : ElfW, link_map;
}
else
{
    static assert(0, "unimplemented");
}

debug (PRINTF) import core.stdc.stdio : printf;

alias SectionGroup = DSO;
struct DSO
{
    static int opApply(scope int delegate(ref DSO) dg)
    {
        foreach (dso; _loadedDSOs)
        {
            if (auto res = dg(*dso))
                return res;
        }
        return 0;
    }

    static int opApplyReverse(scope int delegate(ref DSO) dg)
    {
        foreach_reverse (dso; _loadedDSOs)
        {
            if (auto res = dg(*dso))
                return res;
        }
        return 0;
    }

    @property immutable(ModuleInfo*)[] modules() const nothrow @nogc
    {
        return _moduleGroup.modules;
    }

    @property ref inout(ModuleGroup) moduleGroup() inout return nothrow @nogc
    {
        return _moduleGroup;
    }

    version (DigitalMars)
    @property immutable(FuncTable)[] ehTables() const nothrow @nogc
    {
        return null;
    }

    @property inout(void[])[] gcRanges() inout nothrow @nogc
    {
        return _gcRanges[];
    }

private:

    invariant
    {
        safeAssert(_moduleGroup.modules.length > 0, "No modules for DSO.");
        version (CRuntime_UClibc) {} else
        safeAssert(_tlsMod || !_tlsSize, "Inconsistent TLS fields for DSO.");
    }

    ModuleGroup _moduleGroup;
    Array!(void[]) _gcRanges;
    size_t _tlsMod;
    size_t _tlsSize;

    version (Shared)
    {
        Array!(void[]) _codeSegments; // array of code segments
        Array!(DSO*) _deps; // D libraries needed by this DSO
        void* _handle; // corresponding handle
    }

    // get the TLS range for the executing thread
    void[] tlsRange() const nothrow @nogc
    {
        return getTLSRange(_tlsMod, _tlsSize);
    }
}


version (FreeBSD) private __gshared void* dummy_ref;
version (DragonFlyBSD) private __gshared void* dummy_ref;
version (NetBSD) private __gshared void* dummy_ref;

/****
 * Gets called on program startup just before GC is initialized.
 */
void initSections() nothrow @nogc
{
    // reference symbol to support weak linkage
    version (FreeBSD) dummy_ref = &_d_dso_registry;
    version (DragonFlyBSD) dummy_ref = &_d_dso_registry;
    version (NetBSD) dummy_ref = &_d_dso_registry;
}


/***
 * Gets called on program shutdown just after GC is terminated.
 */
void finiSections() nothrow @nogc
{
}

alias ScanDG = void delegate(void* pbeg, void* pend) nothrow;

version (Shared)
{
    /***
     * Called once per thread; returns array of thread local storage ranges
     */
    Array!(ThreadDSO)* initTLSRanges() @nogc nothrow
    {
        return &_loadedDSOs();
    }

    void finiTLSRanges(Array!(ThreadDSO)* tdsos) @nogc nothrow
    {
        // Nothing to do here. tdsos used to point to the _loadedDSOs instance
        // in the dying thread's TLS segment and as such is not valid anymore.
        // The memory for the array contents was already reclaimed in
        // cleanupLoadedLibraries().
    }

    void scanTLSRanges(Array!(ThreadDSO)* tdsos, scope ScanDG dg) nothrow
    {
        foreach (ref tdso; *tdsos)
            dg(tdso._tlsRange.ptr, tdso._tlsRange.ptr + tdso._tlsRange.length);
    }

    size_t sizeOfTLS() nothrow @nogc
    {
        auto tdsos = initTLSRanges();
        size_t sum;
        foreach (ref tdso; *tdsos)
            sum += tdso._tlsRange.length;
        return sum;
    }

    // interface for core.thread to inherit loaded libraries
    void* pinLoadedLibraries() nothrow @nogc
    {
        auto res = cast(Array!(ThreadDSO)*).calloc(1, Array!(ThreadDSO).sizeof);
        res.length = _loadedDSOs.length;
        foreach (i, ref tdso; _loadedDSOs)
        {
            (*res)[i] = tdso;
            if (tdso._addCnt)
            {
                // Increment the dlopen ref for explicitly loaded libraries to pin them.
                const success = .dlopen(linkMapForHandle(tdso._pdso._handle).l_name, RTLD_LAZY) !is null;
                safeAssert(success, "Failed to increment dlopen ref.");
                (*res)[i]._addCnt = 1; // new array takes over the additional ref count
            }
        }
        return res;
    }

    void unpinLoadedLibraries(void* p) nothrow @nogc
    {
        auto pary = cast(Array!(ThreadDSO)*)p;
        // In case something failed we need to undo the pinning.
        foreach (ref tdso; *pary)
        {
            if (tdso._addCnt)
            {
                auto handle = tdso._pdso._handle;
                safeAssert(handle !is null, "Invalid library handle.");
                .dlclose(handle);
            }
        }
        pary.reset();
        .free(pary);
    }

    // Called before TLS ctors are ran, copy over the loaded libraries
    // of the parent thread.
    void inheritLoadedLibraries(void* p) nothrow @nogc
    {
        safeAssert(_loadedDSOs.empty, "DSOs have already been registered for this thread.");
        _loadedDSOs.swap(*cast(Array!(ThreadDSO)*)p);
        .free(p);
        foreach (ref dso; _loadedDSOs)
        {
            // the copied _tlsRange corresponds to parent thread
            dso.updateTLSRange();
        }
    }

    // Called after all TLS dtors ran, decrements all remaining dlopen refs.
    void cleanupLoadedLibraries() nothrow @nogc
    {
        foreach (ref tdso; _loadedDSOs)
        {
            if (tdso._addCnt == 0) continue;

            auto handle = tdso._pdso._handle;
            safeAssert(handle !is null, "Invalid DSO handle.");
            for (; tdso._addCnt > 0; --tdso._addCnt)
                .dlclose(handle);
        }

        // Free the memory for the array contents.
        _loadedDSOs.reset();
    }
}
else
{
    /***
     * Called once per thread; returns array of thread local storage ranges
     */
    Array!(void[])* initTLSRanges() nothrow @nogc
    {
        auto rngs = &_tlsRanges();
        if (rngs.empty)
        {
            foreach (ref pdso; _loadedDSOs)
                rngs.insertBack(pdso.tlsRange());
        }
        return rngs;
    }

    void finiTLSRanges(Array!(void[])* rngs) nothrow @nogc
    {
        rngs.reset();
        .free(rngs);
    }

    void scanTLSRanges(Array!(void[])* rngs, scope ScanDG dg) nothrow
    {
        foreach (rng; *rngs)
            dg(rng.ptr, rng.ptr + rng.length);
    }

    size_t sizeOfTLS() nothrow @nogc
    {
        auto rngs = initTLSRanges();
        size_t sum;
        foreach (rng; *rngs)
            sum += rng.length;
        return sum;
    }
}

private:

// start of linked list for ModuleInfo references
version (FreeBSD) deprecated extern (C) __gshared void* _Dmodule_ref;
version (DragonFlyBSD) deprecated extern (C) __gshared void* _Dmodule_ref;
version (NetBSD) deprecated extern (C) __gshared void* _Dmodule_ref;

version (Shared)
{
    /*
     * Array of thread local DSO metadata for all libraries loaded and
     * initialized in this thread.
     *
     * Note:
     *     A newly spawned thread will inherit these libraries.
     * Note:
     *     We use an array here to preserve the order of
     *     initialization.  If that became a performance issue, we
     *     could use a hash table and enumerate the DSOs during
     *     loading so that the hash table values could be sorted when
     *     necessary.
     */
    struct ThreadDSO
    {
        DSO* _pdso;
        static if (_pdso.sizeof == 8) uint _refCnt, _addCnt;
        else static if (_pdso.sizeof == 4) ushort _refCnt, _addCnt;
        else static assert(0, "unimplemented");
        void[] _tlsRange;
        alias _pdso this;
        // update the _tlsRange for the executing thread
        void updateTLSRange() nothrow @nogc
        {
            _tlsRange = _pdso.tlsRange();
        }
    }
    @property ref Array!(ThreadDSO) _loadedDSOs() @nogc nothrow { static Array!(ThreadDSO) x; return x; }
    //Array!(ThreadDSO) _loadedDSOs;

    /*
     * Set to true during rt_loadLibrary/rt_unloadLibrary calls.
     */
    bool _rtLoading;

    /*
     * Hash table to map link_map* to corresponding DSO*.
     * The hash table is protected by a Mutex.
     */
    __gshared pthread_mutex_t _handleToDSOMutex;
    @property ref HashTab!(void*, DSO*) _handleToDSO() @nogc nothrow { __gshared HashTab!(void*, DSO*) x; return x; }
    //__gshared HashTab!(void*, DSO*) _handleToDSO;
}
else
{
    /*
     * Static DSOs loaded by the runtime linker. This includes the
     * executable. These can't be unloaded.
     */
    @property ref Array!(DSO*) _loadedDSOs() @nogc nothrow { __gshared Array!(DSO*) x; return x; }
    //__gshared Array!(DSO*) _loadedDSOs;

    /*
     * Thread local array that contains TLS memory ranges for each
     * library initialized in this thread.
     */
    @property ref Array!(void[]) _tlsRanges() @nogc nothrow {
        static Array!(void[])* x = null;
        if (x is null)
            x = cast(Array!(void[])*).calloc(1, Array!(void[]).sizeof);
        safeAssert(x !is null, "Failed to allocate TLS ranges");
        return *x;
    }
    //Array!(void[]) _tlsRanges;

    enum _rtLoading = false;
}

///////////////////////////////////////////////////////////////////////////////
// Compiler to runtime interface.
///////////////////////////////////////////////////////////////////////////////


/*
 * This data structure is generated by the compiler, and then passed to
 * _d_dso_registry().
 */
struct CompilerDSOData
{
    size_t _version;                                       // currently 1
    void** _slot;                                          // can be used to store runtime data
    immutable(object.ModuleInfo*)* _minfo_beg, _minfo_end; // array of modules in this object file
}

T[] toRange(T)(T* beg, T* end) { return beg[0 .. end - beg]; }

/* For each shared library and executable, the compiler generates code that
 * sets up CompilerDSOData and calls _d_dso_registry().
 * A pointer to that code is inserted into both the .init_array and .fini_array
 * segment so it gets called by the loader on startup and shutdown.
 */
extern(C) void _d_dso_registry(CompilerDSOData* data)
{
    // only one supported currently
    safeAssert(data._version >= 1, "Incompatible compiler-generated DSO data version.");

    // no backlink => register
    if (*data._slot is null)
    {
        immutable firstDSO = _loadedDSOs.empty;
        if (firstDSO) initLocks();

        DSO* pdso = cast(DSO*).calloc(1, DSO.sizeof);
        static assert(__traits(isZeroInit, DSO));
        *data._slot = pdso; // store backlink in library record

        pdso._moduleGroup = ModuleGroup(toRange(data._minfo_beg, data._minfo_end));

        SharedObject object = void;
        const objectFound = SharedObject.findForAddress(data._slot, object);
        safeAssert(objectFound, "Failed to find shared ELF object.");

        scanSegments(object, pdso);

        version (Shared)
        {
            auto handle = handleForAddr(data._slot);

            getDependencies(object, pdso._deps);
            pdso._handle = handle;
            setDSOForHandle(pdso, pdso._handle);

            if (!_rtLoading)
            {
                /* This DSO was not loaded by rt_loadLibrary which
                 * happens for all dependencies of an executable or
                 * the first dlopen call from a C program.
                 * In this case we add the DSO to the _loadedDSOs of this
                 * thread with a refCnt of 1 and call the TlsCtors.
                 */
                immutable ushort refCnt = 1, addCnt = 0;
                _loadedDSOs.insertBack(ThreadDSO(pdso, refCnt, addCnt, pdso.tlsRange()));
            }
        }
        else
        {
            foreach (p; _loadedDSOs)
                safeAssert(p !is pdso, "DSO already registered.");
            _loadedDSOs.insertBack(pdso);
            _tlsRanges.insertBack(pdso.tlsRange());
        }

        // don't initialize modules before rt_init was called (see Bugzilla 11378)
        if (isRuntimeInitialized())
        {
            registerGCRanges(pdso);
            // rt_loadLibrary will run tls ctors, so do this only for dlopen
            immutable runTlsCtors = !_rtLoading;
            runModuleConstructors(pdso, runTlsCtors);
        }
    }
    // has backlink => unregister
    else
    {
        DSO* pdso = cast(DSO*)*data._slot;
        *data._slot = null;

        // don't finalizes modules after rt_term was called (see Bugzilla 11378)
        if (isRuntimeInitialized())
        {
            // rt_unloadLibrary already ran tls dtors, so do this only for dlclose
            immutable runTlsDtors = !_rtLoading;
            runModuleDestructors(pdso, runTlsDtors);
            unregisterGCRanges(pdso);
            // run finalizers after module dtors (same order as in rt_term)
            version (Shared) runFinalizers(pdso);
        }

        version (Shared)
        {
            if (!_rtLoading)
            {
                /* This DSO was not unloaded by rt_unloadLibrary so we
                 * have to remove it from _loadedDSOs here.
                 */
                foreach (i, ref tdso; _loadedDSOs)
                {
                    if (tdso._pdso == pdso)
                    {
                        _loadedDSOs.remove(i);
                        break;
                    }
                }
            }

            unsetDSOForHandle(pdso, pdso._handle);
        }
        else
        {
            // static DSOs are unloaded in reverse order
            safeAssert(pdso == _loadedDSOs.back, "DSO being unregistered isn't current last one.");
            _loadedDSOs.popBack();
        }

        freeDSO(pdso);

        // last DSO being unloaded => shutdown registry
        if (_loadedDSOs.empty)
        {
            version (Shared)
            {
                safeAssert(_handleToDSO.empty, "_handleToDSO not in sync with _loadedDSOs.");
                _handleToDSO.reset();
            }
            finiLocks();
        }
    }
}

///////////////////////////////////////////////////////////////////////////////
// dynamic loading
///////////////////////////////////////////////////////////////////////////////

// Shared D libraries are only supported when linking against a shared druntime library.

version (Shared)
{
    ThreadDSO* findThreadDSO(DSO* pdso) nothrow @nogc
    {
        foreach (ref tdata; _loadedDSOs)
            if (tdata._pdso == pdso) return &tdata;
        return null;
    }

    void incThreadRef(DSO* pdso, bool incAdd)
    {
        if (auto tdata = findThreadDSO(pdso)) // already initialized
        {
            if (incAdd && ++tdata._addCnt > 1) return;
            ++tdata._refCnt;
        }
        else
        {
            foreach (dep; pdso._deps)
                incThreadRef(dep, false);
            immutable ushort refCnt = 1, addCnt = incAdd ? 1 : 0;
            _loadedDSOs.insertBack(ThreadDSO(pdso, refCnt, addCnt, pdso.tlsRange()));
            pdso._moduleGroup.runTlsCtors();
        }
    }

    void decThreadRef(DSO* pdso, bool decAdd)
    {
        auto tdata = findThreadDSO(pdso);
        safeAssert(tdata !is null, "Failed to find thread DSO.");
        safeAssert(!decAdd || tdata._addCnt > 0, "Mismatching rt_unloadLibrary call.");

        if (decAdd && --tdata._addCnt > 0) return;
        if (--tdata._refCnt > 0) return;

        pdso._moduleGroup.runTlsDtors();
        foreach (i, ref td; _loadedDSOs)
            if (td._pdso == pdso) _loadedDSOs.remove(i);
        foreach (dep; pdso._deps)
            decThreadRef(dep, false);
    }

    extern(C) void* rt_loadLibrary(const char* name)
    {
        immutable save = _rtLoading;
        _rtLoading = true;
        scope (exit) _rtLoading = save;

        auto handle = .dlopen(name, RTLD_LAZY);
        if (handle is null) return null;

        // if it's a D library
        if (auto pdso = dsoForHandle(handle))
            incThreadRef(pdso, true);
        return handle;
    }

    extern(C) int rt_unloadLibrary(void* handle)
    {
        if (handle is null) return false;

        immutable save = _rtLoading;
        _rtLoading = true;
        scope (exit) _rtLoading = save;

        // if it's a D library
        if (auto pdso = dsoForHandle(handle))
            decThreadRef(pdso, true);
        return .dlclose(handle) == 0;
    }
}

///////////////////////////////////////////////////////////////////////////////
// helper functions
///////////////////////////////////////////////////////////////////////////////

void initLocks() nothrow @nogc
{
    version (Shared)
        !pthread_mutex_init(&_handleToDSOMutex, null) || assert(0);
}

void finiLocks() nothrow @nogc
{
    version (Shared)
        !pthread_mutex_destroy(&_handleToDSOMutex) || assert(0);
}

void runModuleConstructors(DSO* pdso, bool runTlsCtors)
{
    pdso._moduleGroup.sortCtors();
    pdso._moduleGroup.runCtors();
    if (runTlsCtors) pdso._moduleGroup.runTlsCtors();
}

void runModuleDestructors(DSO* pdso, bool runTlsDtors)
{
    if (runTlsDtors) pdso._moduleGroup.runTlsDtors();
    pdso._moduleGroup.runDtors();
}

void registerGCRanges(DSO* pdso) nothrow @nogc
{
    foreach (rng; pdso._gcRanges)
        GC.addRange(rng.ptr, rng.length);
}

void unregisterGCRanges(DSO* pdso) nothrow @nogc
{
    foreach (rng; pdso._gcRanges)
        GC.removeRange(rng.ptr);
}

version (Shared) void runFinalizers(DSO* pdso)
{
    foreach (seg; pdso._codeSegments)
        GC.runFinalizers(seg);
}

void freeDSO(DSO* pdso) nothrow @nogc
{
    pdso._gcRanges.reset();
    version (Shared)
    {
        pdso._codeSegments.reset();
        pdso._deps.reset();
        pdso._handle = null;
    }
    .free(pdso);
}

version (Shared)
{
@nogc nothrow:
    link_map* linkMapForHandle(void* handle)
    {
        link_map* map;
        const success = dlinfo(handle, RTLD_DI_LINKMAP, &map) == 0;
        safeAssert(success, "Failed to get DSO info.");
        return map;
    }

     link_map* exeLinkMap(link_map* map)
     {
         safeAssert(map !is null, "Invalid link_map.");
         while (map.l_prev !is null)
             map = map.l_prev;
         return map;
     }

    DSO* dsoForHandle(void* handle)
    {
        DSO* pdso;
        !pthread_mutex_lock(&_handleToDSOMutex) || assert(0);
        if (auto ppdso = handle in _handleToDSO)
            pdso = *ppdso;
        !pthread_mutex_unlock(&_handleToDSOMutex) || assert(0);
        return pdso;
    }

    void setDSOForHandle(DSO* pdso, void* handle)
    {
        !pthread_mutex_lock(&_handleToDSOMutex) || assert(0);
        safeAssert(handle !in _handleToDSO, "DSO already registered.");
        _handleToDSO[handle] = pdso;
        !pthread_mutex_unlock(&_handleToDSOMutex) || assert(0);
    }

    void unsetDSOForHandle(DSO* pdso, void* handle)
    {
        !pthread_mutex_lock(&_handleToDSOMutex) || assert(0);
        safeAssert(_handleToDSO[handle] == pdso, "Handle doesn't match registered DSO.");
        _handleToDSO.remove(handle);
        !pthread_mutex_unlock(&_handleToDSOMutex) || assert(0);
    }

    void getDependencies(const scope ref SharedObject object, ref Array!(DSO*) deps)
    {
        // get the entries of the .dynamic section
        ElfW!"Dyn"[] dyns;
        foreach (ref phdr; object)
        {
            if (phdr.p_type == PT_DYNAMIC)
            {
                auto p = cast(ElfW!"Dyn"*)(object.baseAddress + (phdr.p_vaddr & ~(size_t.sizeof - 1)));
                dyns = p[0 .. phdr.p_memsz / ElfW!"Dyn".sizeof];
                break;
            }
        }
        // find the string table which contains the sonames
        const(char)* strtab;
        foreach (dyn; dyns)
        {
            if (dyn.d_tag == DT_STRTAB)
            {
                version (CRuntime_Musl)
                    enum relocate = true;
                else version (linux)
                {
                    // This might change in future glibc releases (after 2.29) as dynamic sections
                    // are not required to be read-only on RISC-V. This was copy & pasted from MIPS
                    // while upstreaming RISC-V support. Otherwise MIPS is the only arch which sets
                    // in glibc: #define DL_RO_DYN_SECTION 1
                    version (RISCV_Any)     enum relocate = true;
                    else version (MIPS_Any) enum relocate = true;
                    else                    enum relocate = false;
                }
                else version (FreeBSD)
                    enum relocate = true;
                else version (NetBSD)
                    enum relocate = true;
                else version (DragonFlyBSD)
                    enum relocate = true;
                else
                    static assert(0, "unimplemented");

                const base = relocate ? cast(const char*) object.baseAddress : null;
                strtab = base + dyn.d_un.d_ptr;

                break;
            }
        }
        foreach (dyn; dyns)
        {
            immutable tag = dyn.d_tag;
            if (!(tag == DT_NEEDED || tag == DT_AUXILIARY || tag == DT_FILTER))
                continue;

            // soname of the dependency
            auto name = strtab + dyn.d_un.d_val;
            // get handle without loading the library
            auto handle = handleForName(name);
            // the runtime linker has already loaded all dependencies
            safeAssert(handle !is null, "Failed to get library handle.");
            // if it's a D library
            if (auto pdso = dsoForHandle(handle))
                deps.insertBack(pdso); // append it to the dependencies
        }
    }

    void* handleForName(const char* name)
    {
        auto handle = .dlopen(name, RTLD_NOLOAD | RTLD_LAZY);
        if (handle !is null) .dlclose(handle); // drop reference count
        return handle;
    }
}

///////////////////////////////////////////////////////////////////////////////
// Elf program header iteration
///////////////////////////////////////////////////////////////////////////////

/************
 * Scan segments in Linux dl_phdr_info struct and store
 * the TLS and writeable data segments in *pdso.
 */
void scanSegments(const scope ref SharedObject object, DSO* pdso) nothrow @nogc
{
    foreach (ref phdr; object)
    {
        switch (phdr.p_type)
        {
        case PT_LOAD:
            if (phdr.p_flags & PF_W) // writeable data segment
            {
                auto beg = object.baseAddress + (phdr.p_vaddr & ~(size_t.sizeof - 1));
                pdso._gcRanges.insertBack(beg[0 .. phdr.p_memsz]);
            }
            version (Shared) if (phdr.p_flags & PF_X) // code segment
            {
                auto beg = object.baseAddress + (phdr.p_vaddr & ~(size_t.sizeof - 1));
                pdso._codeSegments.insertBack(beg[0 .. phdr.p_memsz]);
            }
            break;

        case PT_TLS: // TLS segment
            safeAssert(!pdso._tlsSize, "Multiple TLS segments in image header.");
            version (CRuntime_UClibc)
            {
                // uClibc doesn't provide a 'dlpi_tls_modid' definition
            }
            else
                pdso._tlsMod = object.info.dlpi_tls_modid;
            pdso._tlsSize = phdr.p_memsz;
            break;

        default:
            break;
        }
    }
}

/**************************
 * Input:
 *      addr  an internal address of a DSO
 * Returns:
 *      the dlopen handle for that DSO or null if addr is not within a loaded DSO
 */
version (Shared) void* handleForAddr(void* addr) nothrow @nogc
{
    Dl_info info = void;
    if (dladdr(addr, &info) != 0)
        return handleForName(info.dli_fname);
    return null;
}

///////////////////////////////////////////////////////////////////////////////
// TLS module helper
///////////////////////////////////////////////////////////////////////////////


/*
 * Returns: the TLS memory range for a given module and the calling
 * thread or null if that module has no TLS.
 *
 * Note: This will cause the TLS memory to be eagerly allocated.
 */
struct tls_index
{
    version (CRuntime_Glibc)
    {
        // For x86_64, fields are of type uint64_t, this is important for x32
        // where tls_index would otherwise have the wrong size.
        // See https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/x86_64/dl-tls.h
        version (X86_64)
        {
            ulong ti_module;
            ulong ti_offset;
        }
        else
        {
            c_ulong ti_module;
            c_ulong ti_offset;
        }
    }
    else
    {
        size_t ti_module;
        size_t ti_offset;
    }
}

extern(C) void* __tls_get_addr(tls_index* ti) nothrow @nogc;

/* The dynamic thread vector (DTV) pointers may point 0x8000 past the start of
 * each TLS block. This is at least true for PowerPC and Mips platforms.
 * See: https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/powerpc/dl-tls.h;h=f7cf6f96ebfb505abfd2f02be0ad0e833107c0cd;hb=HEAD#l34
 *      https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/mips/dl-tls.h;h=93a6dc050cb144b9f68b96fb3199c60f5b1fcd18;hb=HEAD#l32
 *      https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/riscv/dl-tls.h;h=ab2d860314de94c18812bc894ff6b3f55368f20f;hb=HEAD#l32
 */
version (X86)
    enum TLS_DTV_OFFSET = 0x0;
else version (X86_64)
    enum TLS_DTV_OFFSET = 0x0;
else version (ARM)
    enum TLS_DTV_OFFSET = 0x0;
else version (AArch64)
    enum TLS_DTV_OFFSET = 0x0;
else version (RISCV_Any)
    enum TLS_DTV_OFFSET = 0x800;
else version (HPPA)
    enum TLS_DTV_OFFSET = 0x0;
else version (SPARC)
    enum TLS_DTV_OFFSET = 0x0;
else version (SPARC64)
    enum TLS_DTV_OFFSET = 0x0;
else version (PPC)
    enum TLS_DTV_OFFSET = 0x8000;
else version (PPC64)
    enum TLS_DTV_OFFSET = 0x8000;
else version (MIPS_Any)
    enum TLS_DTV_OFFSET = 0x8000;
else version (LoongArch64)
    enum TLS_DTV_OFFSET = 0x0;
else
    static assert( false, "Platform not supported." );

void[] getTLSRange(size_t mod, size_t sz) nothrow @nogc
{
    if (mod == 0)
        return null;

    // base offset
    auto ti = tls_index(mod, 0);
    return (__tls_get_addr(&ti)-TLS_DTV_OFFSET)[0 .. sz];
}
