ClickHouse/libs/libcommon/src/phdr_cache.cpp

/// This code was developed by Fedor Korotkiy (prime@yandex-team.ru) for YT product in Yandex.

#include <link.h>
#include <dlfcn.h>
#include <vector>
#include <atomic>
#include <cstddef>
#include <stdexcept>


#if defined(__has_feature)
    #if __has_feature(address_sanitizer)
        #define ADDRESS_SANITIZER 1
    #endif
#elif defined(__SANITIZE_ADDRESS__)
    #define ADDRESS_SANITIZER 1
#endif

extern "C"
{
#ifdef ADDRESS_SANITIZER
void __lsan_ignore_object(const void *);
#else
void __lsan_ignore_object(const void *) {}
#endif
}


namespace
{

// This is adapted from
// https://github.com/scylladb/seastar/blob/master/core/exception_hacks.hh
// https://github.com/scylladb/seastar/blob/master/core/exception_hacks.cc

using DLIterateFunction = int (*) (int (*callback) (dl_phdr_info * info, size_t size, void * data), void * data);

DLIterateFunction getOriginalDLIteratePHDR()
{
    void * func = dlsym(RTLD_NEXT, "dl_iterate_phdr");
    if (!func)
        throw std::runtime_error("Cannot find dl_iterate_phdr function with dlsym");
    return reinterpret_cast<DLIterateFunction>(func);
}


using PHDRCache = std::vector<dl_phdr_info>;
std::atomic<PHDRCache *> phdr_cache {};

}


extern "C"
#ifndef __clang__
[[gnu::visibility("default")]]
[[gnu::externally_visible]]
#endif
int dl_iterate_phdr(int (*callback) (dl_phdr_info * info, size_t size, void * data), void * data)
{
    auto current_phdr_cache = phdr_cache.load(std::memory_order_relaxed);
    if (!current_phdr_cache)
    {
        // Cache is not yet populated, pass through to the original function.
        return getOriginalDLIteratePHDR()(callback, data);
    }

    int result = 0;
    for (auto & entry : *current_phdr_cache)
    {
        result = callback(&entry, offsetof(dl_phdr_info, dlpi_adds), data);
        if (result != 0)
            break;
    }
    return result;
}


void updatePHDRCache()
{
#if defined(__linux__)
    // Fill out ELF header cache for access without locking.
    // This assumes no dynamic object loading/unloading after this point

    PHDRCache * new_phdr_cache = new PHDRCache;
    getOriginalDLIteratePHDR()([] (dl_phdr_info * info, size_t /*size*/, void * data)
    {
        reinterpret_cast<PHDRCache *>(data)->push_back(*info);
        return 0;
    }, new_phdr_cache);
    phdr_cache.store(new_phdr_cache);

    /// Memory is intentionally leaked.
    __lsan_ignore_object(new_phdr_cache);

#endif
}