llvm-project/compiler-rt/lib/profile/InstrProfilingRuntime.cpp

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//===- InstrProfilingRuntime.cpp - PGO runtime initialization -------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
extern "C" {
#include "InstrProfiling.h"
/* int __llvm_profile_runtime */
COMPILER_RT_VISIBILITY int INSTR_PROF_PROFILE_RUNTIME_VAR;
}
namespace {
class RegisterRuntime {
public:
RegisterRuntime() {
__llvm_profile_initialize_file();
[profile] Add a mode to continuously sync counter updates to a file Add support for continuously syncing profile counter updates to a file. The motivation for this is that programs do not always exit cleanly. On iOS, for example, programs are usually killed via a signal from the OS. Running atexit() handlers after catching a signal is unreliable, so some method for progressively writing out profile data is necessary. The approach taken here is to mmap() the `__llvm_prf_cnts` section onto a raw profile. To do this, the linker must page-align the counter and data sections, and the runtime must ensure that counters are mapped to a page-aligned offset within a raw profile. Continuous mode is (for the moment) incompatible with the online merging mode. This limitation is lifted in https://reviews.llvm.org/D69586. Continuous mode is also (for the moment) incompatible with value profiling, as I'm not sure whether there is interest in this and the implementation may be tricky. As I have not been able to test extensively on non-Darwin platforms, only Darwin support is included for the moment. However, continuous mode may "just work" without modification on Linux and some UNIX-likes. AIUI the default value for the GNU linker's `--section-alignment` flag is set to the page size on many systems. This appears to be true for LLD as well, as its `no_nmagic` option is on by default. Continuous mode will not "just work" on Fuchsia or Windows, as it's not possible to mmap() a section on these platforms. There is a proposal to add a layer of indirection to the profile instrumentation to support these platforms. rdar://54210980 Differential Revision: https://reviews.llvm.org/D68351
2019-09-20 02:56:43 +08:00
if (!__llvm_profile_is_continuous_mode_enabled())
__llvm_profile_register_write_file_atexit();
}
};
RegisterRuntime Registration;
}