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| 1 | +// Copyright 2019-2020 CERN and copyright holders of ALICE O2. |
| 2 | +// See https://alice-o2.web.cern.ch/copyright for details of the copyright holders. |
| 3 | +// All rights not expressly granted are reserved. |
| 4 | +// |
| 5 | +// This software is distributed under the terms of the GNU General Public |
| 6 | +// License v3 (GPL Version 3), copied verbatim in the file "COPYING". |
| 7 | +// |
| 8 | +// In applying this license CERN does not waive the privileges and immunities |
| 9 | +// granted to it by virtue of its status as an Intergovernmental Organization |
| 10 | +// or submit itself to any jurisdiction. |
| 11 | + |
| 12 | +#ifndef O2_SIMSETUP_STATICTLSRESERVE_H |
| 13 | +#define O2_SIMSETUP_STATICTLSRESERVE_H |
| 14 | + |
| 15 | +#include <cerrno> |
| 16 | +#include <charconv> |
| 17 | +#include <climits> |
| 18 | +#include <cstdio> |
| 19 | +#include <cstdlib> |
| 20 | +#include <cstring> |
| 21 | +#include <string> |
| 22 | +#include <string_view> |
| 23 | +#include <unistd.h> |
| 24 | + |
| 25 | +namespace o2 |
| 26 | +{ |
| 27 | + |
| 28 | +/// Static TLS reserve in bytes for a Geant4 built with the initial-exec TLS model and loaded by dlopen |
| 29 | +constexpr unsigned long Geant4StaticTLSReserve = 32768; |
| 30 | + |
| 31 | +/// The GLIBC_TUNABLES value with a static TLS reserve of at least `reserve` bytes, or an empty string if |
| 32 | +/// `tunables` already has one. As in glibc, the last well-formed reserve counts. Other tunables are kept. |
| 33 | +inline std::string withStaticTLSReserve(const char* tunables, unsigned long reserve = Geant4StaticTLSReserve) |
| 34 | +{ |
| 35 | + constexpr std::string_view name = "glibc.rtld.optional_static_tls"; |
| 36 | + std::string kept; |
| 37 | + bool haveReserve = false; |
| 38 | + unsigned long current = 0; |
| 39 | + std::string_view rest = tunables ? tunables : ""; |
| 40 | + while (!rest.empty()) { |
| 41 | + const auto colon = rest.find(':'); |
| 42 | + const std::string_view entry = rest.substr(0, colon); |
| 43 | + rest = colon == std::string_view::npos ? std::string_view{} : rest.substr(colon + 1); |
| 44 | + const auto equal = entry.find('='); |
| 45 | + if (entry.substr(0, equal) == name) { |
| 46 | + const std::string_view value = equal == std::string_view::npos ? std::string_view{} : entry.substr(equal + 1); |
| 47 | + unsigned long bytes = 0; |
| 48 | + const auto [end, ec] = std::from_chars(value.data(), value.data() + value.size(), bytes); |
| 49 | + if (!value.empty() && ec == std::errc() && end == value.data() + value.size()) { |
| 50 | + haveReserve = true; |
| 51 | + current = bytes; |
| 52 | + } |
| 53 | + continue; // our own entry replaces all of them |
| 54 | + } |
| 55 | + if (!entry.empty()) { |
| 56 | + kept += (kept.empty() ? "" : ":") + std::string(entry); |
| 57 | + } |
| 58 | + } |
| 59 | + if (haveReserve && current >= reserve) { |
| 60 | + return {}; |
| 61 | + } |
| 62 | + return std::string(name) + "=" + std::to_string(reserve) + (kept.empty() ? "" : ":" + kept); |
| 63 | +} |
| 64 | + |
| 65 | +/// Sets the static TLS reserve in the environment, for the programs started from here. Returns true if it changed. |
| 66 | +inline bool setStaticTLSReserve(unsigned long reserve = Geant4StaticTLSReserve) |
| 67 | +{ |
| 68 | + const auto tunables = withStaticTLSReserve(getenv("GLIBC_TUNABLES"), reserve); |
| 69 | + if (tunables.empty()) { |
| 70 | + return false; |
| 71 | + } |
| 72 | + setenv("GLIBC_TUNABLES", tunables.c_str(), 1); |
| 73 | + return true; |
| 74 | +} |
| 75 | + |
| 76 | +/// Restarts the program once with the static TLS reserve if it lacks one. glibc reads GLIBC_TUNABLES only at |
| 77 | +/// program start, so the reserve cannot be set later. Call this first in main, before any thread is started. |
| 78 | +inline void ensureStaticTLSReserve([[maybe_unused]] char* argv[], |
| 79 | + [[maybe_unused]] unsigned long reserve = Geant4StaticTLSReserve) |
| 80 | +{ |
| 81 | +#ifdef __linux__ |
| 82 | + constexpr const char* guard = "O2_STATIC_TLS_REEXEC"; |
| 83 | + if (getenv(guard)) { |
| 84 | + unsetenv(guard); // restarted already; do not loop if glibc ignores the tunable |
| 85 | + return; |
| 86 | + } |
| 87 | + if (withStaticTLSReserve(getenv("GLIBC_TUNABLES"), reserve).empty()) { |
| 88 | + return; |
| 89 | + } |
| 90 | + // the real path keeps the process name; /proc/self/exe would rename it to "exe" |
| 91 | + char self[PATH_MAX]; |
| 92 | + const auto length = readlink("/proc/self/exe", self, sizeof(self) - 1); |
| 93 | + if (length <= 0) { |
| 94 | + return; |
| 95 | + } |
| 96 | + self[length] = '\0'; |
| 97 | + const char* base = strrchr(self, '/'); |
| 98 | + if (strncmp(base ? base + 1 : self, "ld-", 3) == 0) { |
| 99 | + return; // started through the dynamic loader, which a restart would not reproduce |
| 100 | + } |
| 101 | + setStaticTLSReserve(reserve); |
| 102 | + setenv(guard, "1", 1); |
| 103 | + fprintf(stderr, "Restarting %s with GLIBC_TUNABLES=%s for the static TLS of Geant4\n", self, getenv("GLIBC_TUNABLES")); |
| 104 | + execv(self, argv); |
| 105 | + const int error = errno; |
| 106 | + unsetenv(guard); |
| 107 | + fprintf(stderr, "Restart of %s failed: %s\n", self, strerror(error)); |
| 108 | +#endif |
| 109 | +} |
| 110 | + |
| 111 | +} // namespace o2 |
| 112 | + |
| 113 | +#endif |
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