src/getpc.h

// -*- Mode: C++; c-basic-offset: 2; indent-tabs-mode: nil -*-
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// ---
// Author: Craig Silverstein
//
// This is an internal header file used by profiler.cc.  It defines
// the single (inline) function GetPC.  GetPC is used in a signal
// handler to figure out the instruction that was being executed when
// the signal-handler was triggered.
//
// To get this, we use the ucontext_t argument to the signal-handler
// callback, which holds the full context of what was going on when
// the signal triggered.  How to get from a ucontext_t to a Program
// Counter is OS-dependent.

#ifndef BASE_GETPC_H_
#define BASE_GETPC_H_

// Note: we include this from one of configure script C++ tests as
// part of verifying that we're able to build CPU profiler. I.e. we
// cannot include config.h as we normally do, since it isn't produced
// yet, but those HAVE_XYZ defines are available, so including
// ucontext etc stuff works. It's usage from profiler.cc (and
// stacktrace_generic_fp-inl.h) is after config.h is included.

// On many linux systems, we may need _GNU_SOURCE to get access to
// the defined constants that define the register we want to see (eg
// REG_EIP).  Note this #define must come first!
#define _GNU_SOURCE 1

#ifdef HAVE_ASM_PTRACE_H
#include <asm/ptrace.h>
#endif
#if HAVE_SYS_UCONTEXT_H
#include <sys/ucontext.h>
#elif HAVE_UCONTEXT_H
#include <ucontext.h>       // for ucontext_t (and also mcontext_t)
#elif defined(HAVE_CYGWIN_SIGNAL_H)
#include <cygwin/signal.h>
typedef ucontext ucontext_t;
#endif

namespace tcmalloc {
namespace getpc {

// std::void_t is C++ 14. So we steal this from
// https://en.cppreference.com/w/cpp/types/void_t
template<typename... Ts>
struct make_void { typedef void type; };
template <typename... Ts>
using void_t = typename make_void<Ts...>::type;

#include "getpc-inl.h"

}  // namespace getpc
}  // namespace tcmalloc

// If this doesn't compile, you need to figure out the right value for
// your system, and add it to the list above.
inline void* GetPC(const ucontext_t& signal_ucontext) {
  void* retval = tcmalloc::getpc::internal::RawUCToPC(&signal_ucontext);

#if defined(__s390__) && !defined(__s390x__)
  // Mask out the AMODE31 bit from the PC recorded in the context.
  retval = (void*)((unsigned long)retval & 0x7fffffffUL);
#endif

  return retval;
}

#endif  // BASE_GETPC_H_