From d889d1efefe9f97507e3eafa85a2e3939df9750f Mon Sep 17 00:00:00 2001 From: Vedant Kumar Date: Thu, 19 Sep 2019 11:56:43 -0700 Subject: [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 --- llvm/lib/ProfileData/InstrProfReader.cpp | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) (limited to 'llvm/lib/ProfileData/InstrProfReader.cpp') diff --git a/llvm/lib/ProfileData/InstrProfReader.cpp b/llvm/lib/ProfileData/InstrProfReader.cpp index 23d078a3dde..b904f983dce 100644 --- a/llvm/lib/ProfileData/InstrProfReader.cpp +++ b/llvm/lib/ProfileData/InstrProfReader.cpp @@ -362,7 +362,9 @@ Error RawInstrProfReader::readHeader( CountersDelta = swap(Header.CountersDelta); NamesDelta = swap(Header.NamesDelta); auto DataSize = swap(Header.DataSize); + auto PaddingBytesBeforeCounters = swap(Header.PaddingBytesBeforeCounters); auto CountersSize = swap(Header.CountersSize); + auto PaddingBytesAfterCounters = swap(Header.PaddingBytesAfterCounters); NamesSize = swap(Header.NamesSize); ValueKindLast = swap(Header.ValueKindLast); @@ -370,8 +372,10 @@ Error RawInstrProfReader::readHeader( auto PaddingSize = getNumPaddingBytes(NamesSize); ptrdiff_t DataOffset = sizeof(RawInstrProf::Header); - ptrdiff_t CountersOffset = DataOffset + DataSizeInBytes; - ptrdiff_t NamesOffset = CountersOffset + sizeof(uint64_t) * CountersSize; + ptrdiff_t CountersOffset = + DataOffset + DataSizeInBytes + PaddingBytesBeforeCounters; + ptrdiff_t NamesOffset = CountersOffset + (sizeof(uint64_t) * CountersSize) + + PaddingBytesAfterCounters; ptrdiff_t ValueDataOffset = NamesOffset + NamesSize + PaddingSize; auto *Start = reinterpret_cast(&Header); -- cgit v1.2.3