80c9455413
The CPU cost of iterating over the relevant ELF structures is probably negligible (despite the amount of code involved), but there is no need to keep the containing page mapped in RAM when it doesn't have to be. Signed-off-by: Michael Livshin <michael.livshin@scylladb.com>
82 lines
1.9 KiB
C++
82 lines
1.9 KiB
C++
/*
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* Copyright (C) 2019-present ScyllaDB
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*/
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#include "build_id.hh"
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#include <fmt/ostream.h>
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#include <link.h>
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#include <seastar/core/align.hh>
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#include <sstream>
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#include <cassert>
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using namespace seastar;
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static const Elf64_Nhdr* get_nt_build_id(dl_phdr_info* info) {
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auto base = info->dlpi_addr;
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const auto* h = info->dlpi_phdr;
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auto num_headers = info->dlpi_phnum;
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for (int i = 0; i != num_headers; ++i, ++h) {
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if (h->p_type != PT_NOTE) {
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continue;
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}
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auto* p = reinterpret_cast<const char*>(base + h->p_vaddr);
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auto* e = p + h->p_memsz;
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while (p != e) {
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const auto* n = reinterpret_cast<const Elf64_Nhdr*>(p);
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if (n->n_type == NT_GNU_BUILD_ID) {
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return n;
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}
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p += sizeof(Elf64_Nhdr);
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p += n->n_namesz;
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p = align_up(p, 4);
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p += n->n_descsz;
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p = align_up(p, 4);
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}
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}
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assert(0 && "no NT_GNU_BUILD_ID note");
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}
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static int callback(dl_phdr_info* info, size_t size, void* data) {
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std::string& ret = *(std::string*)data;
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std::ostringstream os;
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// The first DSO is always the main program, which has an empty name.
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assert(strlen(info->dlpi_name) == 0);
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auto* n = get_nt_build_id(info);
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auto* p = reinterpret_cast<const unsigned char*>(n);
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p += sizeof(Elf64_Nhdr);
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p += n->n_namesz;
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p = align_up(p, 4);
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auto* desc = p;
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auto* desc_end = p + n->n_descsz;
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while (desc < desc_end) {
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fmt::print(os, "{:02x}", *desc++);
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}
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ret = os.str();
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return 1;
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}
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static std::string really_get_build_id() {
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std::string ret;
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int r = dl_iterate_phdr(callback, &ret);
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assert(r == 1);
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return ret;
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}
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std::string get_build_id() {
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static thread_local std::string cache;
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if (cache.empty()) {
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cache = really_get_build_id();
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}
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return cache;
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}
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