[llvm] r248897 - Add support for sub-byte aligned writes to lib/Support/Endian.h
Teresa Johnson via llvm-commits
llvm-commits at lists.llvm.org
Wed Oct 7 16:18:15 PDT 2015
Yes, I added that function and see the problem. I will fix the UBSan
error by masking off the upper bits before the shift. It might be
tomorrow morning before I can fix it though as I am going offline
shortly. Will try to get it in today though.
Teresa
On Wed, Oct 7, 2015 at 2:52 PM, Adrian Prantl <aprantl at apple.com> wrote:
> Hi Teresa,
>
> I’m still working on confirming it, but it looks quite plausible that this commit caused the following UBSan test failure on lab.llvm.org:
>
> http://lab.llvm.org:8080/green/job/clang-stage2-cmake-RgSan_check/477/consoleFull#-1567746458254eaf0-7326-4999-85b0-388101f2d404
>
> FAIL: LLVM-Unit :: Support/SupportTests/Endian.WriteBitAligned (23480 of 23746)
>
> ******************** TEST 'LLVM-Unit :: Support/SupportTests/Endian.WriteBitAligned' FAILED ********************
>
> Note: Google Test filter = Endian.WriteBitAligned
> [==========] Running 1 test from 1 test case.
> [----------] Global test environment set-up.
> [----------] 1 test from Endian
> [ RUN ] Endian.WriteBitAligned
> /Users/buildslave/jenkins/sharedspace/clang-stage2-cmake-RgSan at 2/llvm/include/llvm/Support/Endian.h:135:21: runtime error: left shift of negative value -21846
> SUMMARY: AddressSanitizer: undefined-behavior /Users/buildslave/jenkins/sharedspace/clang-stage2-cmake-RgSan at 2/llvm/include/llvm/Support/Endian.h:135:21 in
> 0 SupportTests 0x00000001009c01c3 llvm::sys::PrintStackTrace(llvm::raw_ostream&) + 339
> 1 SupportTests 0x00000001009beaa5 llvm::sys::RunSignalHandlers() + 213
> 2 SupportTests 0x00000001009c143f SignalHandler(int) + 655
> 3 libsystem_platform.dylib 0x00007fff8b72ef1a _sigtramp + 26
> 4 libclang_rt.asan_osx_dynamic.dylib 0x0000000101c0678d getTypeCacheHashTableBucket(unsigned long)::__ubsan_vptr_hash_set + 532925
> 5 libsystem_c.dylib 0x00007fff853459b3 abort + 129
> 6 libclang_rt.asan_osx_dynamic.dylib 0x0000000100ee5f56 __sanitizer::Abort() + 6
>
>
>
> -- adrian
>
>
>> On Sep 30, 2015, at 6:20 AM, Teresa Johnson via llvm-commits <llvm-commits at lists.llvm.org> wrote:
>>
>> Author: tejohnson
>> Date: Wed Sep 30 08:20:37 2015
>> New Revision: 248897
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=248897&view=rev
>> Log:
>> Add support for sub-byte aligned writes to lib/Support/Endian.h
>>
>> Summary:
>> As per Duncan's review for D12536, I extracted the sub-byte bit aligned
>> reading and writing code into lib/Support, and generalized it. Added calls from
>> BackpatchWord. Also added unittests.
>>
>> Reviewers: dexonsmith
>>
>> Subscribers: llvm-commits
>>
>> Differential Revision: http://reviews.llvm.org/D13189
>>
>> Modified:
>> llvm/trunk/include/llvm/Bitcode/BitstreamWriter.h
>> llvm/trunk/include/llvm/Support/Endian.h
>> llvm/trunk/unittests/Support/EndianTest.cpp
>>
>> Modified: llvm/trunk/include/llvm/Bitcode/BitstreamWriter.h
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Bitcode/BitstreamWriter.h?rev=248897&r1=248896&r2=248897&view=diff
>> ==============================================================================
>> --- llvm/trunk/include/llvm/Bitcode/BitstreamWriter.h (original)
>> +++ llvm/trunk/include/llvm/Bitcode/BitstreamWriter.h Wed Sep 30 08:20:37 2015
>> @@ -102,18 +102,13 @@ public:
>> /// Backpatch a 32-bit word in the output at the given bit offset
>> /// with the specified value.
>> void BackpatchWord(uint64_t BitNo, unsigned NewWord) {
>> + using namespace llvm::support;
>> unsigned ByteNo = BitNo / 8;
>> - if ((BitNo & 7) == 0) {
>> - // Already 8-bit aligned
>> - support::endian::write32le(&Out[ByteNo], NewWord);
>> - } else {
>> - uint64_t CurDWord = support::endian::read64le(&Out[ByteNo]);
>> - unsigned StartBit = BitNo & 7;
>> - // Currently expect to backpatch 0-value placeholders.
>> - assert(((CurDWord >> StartBit) & 0xffffffff) == 0);
>> - CurDWord |= NewWord << StartBit;
>> - support::endian::write64le(&Out[ByteNo], CurDWord);
>> - }
>> + assert((!endian::readAtBitAlignment<uint32_t, little, unaligned>(
>> + &Out[ByteNo], BitNo & 7)) &&
>> + "Expected to be patching over 0-value placeholders");
>> + endian::writeAtBitAlignment<uint32_t, little, unaligned>(
>> + &Out[ByteNo], NewWord, BitNo & 7);
>> }
>>
>> void Emit(uint32_t Val, unsigned NumBits) {
>>
>> Modified: llvm/trunk/include/llvm/Support/Endian.h
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Support/Endian.h?rev=248897&r1=248896&r2=248897&view=diff
>> ==============================================================================
>> --- llvm/trunk/include/llvm/Support/Endian.h (original)
>> +++ llvm/trunk/include/llvm/Support/Endian.h Wed Sep 30 08:20:37 2015
>> @@ -77,6 +77,81 @@ inline void write(void *memory, value_ty
>> &value,
>> sizeof(value_type));
>> }
>> +
>> +/// Read a value of a particular endianness from memory, for a location
>> +/// that starts at the given bit offset within the first byte.
>> +template <typename value_type, endianness endian, std::size_t alignment>
>> +inline value_type readAtBitAlignment(const void *memory, uint64_t startBit) {
>> + assert(startBit < 8);
>> + if (startBit == 0)
>> + return read<value_type, endian, alignment>(memory);
>> + else {
>> + // Read two values and compose the result from them.
>> + value_type val[2];
>> + memcpy(&val[0],
>> + LLVM_ASSUME_ALIGNED(
>> + memory, (detail::PickAlignment<value_type, alignment>::value)),
>> + sizeof(value_type) * 2);
>> + val[0] = byte_swap<value_type, endian>(val[0]);
>> + val[1] = byte_swap<value_type, endian>(val[1]);
>> +
>> + // Shift bits from the lower value into place.
>> + unsigned lowerVal = val[0] >> startBit;
>> + // Mask off upper bits after right shift in case of signed type.
>> + unsigned numBitsFirstVal = (sizeof(value_type) * 8) - startBit;
>> + lowerVal &= (1 << numBitsFirstVal) - 1;
>> +
>> + // Get the bits from the upper value.
>> + unsigned upperVal = val[1] & ((1 << startBit) - 1);
>> + // Shift them in to place.
>> + upperVal <<= numBitsFirstVal;
>> +
>> + return lowerVal | upperVal;
>> + }
>> +}
>> +
>> +/// Write a value to memory with a particular endianness, for a location
>> +/// that starts at the given bit offset within the first byte.
>> +template <typename value_type, endianness endian, std::size_t alignment>
>> +inline void writeAtBitAlignment(void *memory, value_type value,
>> + uint64_t startBit) {
>> + assert(startBit < 8);
>> + if (startBit == 0)
>> + write<value_type, endian, alignment>(memory, value);
>> + else {
>> + // Read two values and shift the result into them.
>> + value_type val[2];
>> + memcpy(&val[0],
>> + LLVM_ASSUME_ALIGNED(
>> + memory, (detail::PickAlignment<value_type, alignment>::value)),
>> + sizeof(value_type) * 2);
>> + val[0] = byte_swap<value_type, endian>(val[0]);
>> + val[1] = byte_swap<value_type, endian>(val[1]);
>> +
>> + // Mask off any existing bits in the upper part of the lower value that
>> + // we want to replace.
>> + val[0] &= (1 << startBit) - 1;
>> + // Now shift in the new bits
>> + val[0] |= value << startBit;
>> +
>> + // Mask off any existing bits in the lower part of the upper value that
>> + // we want to replace.
>> + val[1] &= ~((1 << startBit) - 1);
>> + // Next shift the bits that go into the upper value into position.
>> + unsigned numBitsFirstVal = (sizeof(value_type) * 8) - startBit;
>> + unsigned upperVal = value >> numBitsFirstVal;
>> + // Mask off upper bits after right shift in case of signed type.
>> + upperVal &= (1 << startBit) - 1;
>> + val[1] |= upperVal;
>> +
>> + // Finally, rewrite values.
>> + val[0] = byte_swap<value_type, endian>(val[0]);
>> + val[1] = byte_swap<value_type, endian>(val[1]);
>> + memcpy(LLVM_ASSUME_ALIGNED(
>> + memory, (detail::PickAlignment<value_type, alignment>::value)),
>> + &val[0], sizeof(value_type) * 2);
>> + }
>> +}
>> } // end namespace endian
>>
>> namespace detail {
>>
>> Modified: llvm/trunk/unittests/Support/EndianTest.cpp
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/unittests/Support/EndianTest.cpp?rev=248897&r1=248896&r2=248897&view=diff
>> ==============================================================================
>> --- llvm/trunk/unittests/Support/EndianTest.cpp (original)
>> +++ llvm/trunk/unittests/Support/EndianTest.cpp Wed Sep 30 08:20:37 2015
>> @@ -32,6 +32,54 @@ TEST(Endian, Read) {
>> (endian::read<int32_t, little, unaligned>(littleval + 1)));
>> }
>>
>> +TEST(Endian, ReadBitAligned) {
>> + // Simple test to make sure we properly pull out the 0x0 word.
>> + unsigned char littleval[] = {0x3f, 0x00, 0x00, 0x00, 0xc0, 0xff, 0xff, 0xff};
>> + unsigned char bigval[] = {0x00, 0x00, 0x00, 0x3f, 0xff, 0xff, 0xff, 0xc0};
>> + EXPECT_EQ(
>> + (endian::readAtBitAlignment<int, little, unaligned>(&littleval[0], 6)),
>> + 0x0);
>> + EXPECT_EQ((endian::readAtBitAlignment<int, big, unaligned>(&bigval[0], 6)),
>> + 0x0);
>> + // Test to make sure that signed right shift of 0xf0000000 is masked
>> + // properly.
>> + unsigned char littleval2[] = {0x00, 0x00, 0x00, 0xf0, 0x00, 0x00, 0x00, 0x00};
>> + unsigned char bigval2[] = {0xf0, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
>> + EXPECT_EQ(
>> + (endian::readAtBitAlignment<int, little, unaligned>(&littleval2[0], 4)),
>> + 0x0f000000);
>> + EXPECT_EQ((endian::readAtBitAlignment<int, big, unaligned>(&bigval2[0], 4)),
>> + 0x0f000000);
>> +}
>> +
>> +TEST(Endian, WriteBitAligned) {
>> + // This test ensures that signed right shift of 0xffffaa is masked
>> + // properly.
>> + unsigned char bigval[8] = {0x00};
>> + endian::writeAtBitAlignment<int32_t, big, unaligned>(bigval, (int)0xffffaaaa,
>> + 4);
>> + EXPECT_EQ(bigval[0], 0xff);
>> + EXPECT_EQ(bigval[1], 0xfa);
>> + EXPECT_EQ(bigval[2], 0xaa);
>> + EXPECT_EQ(bigval[3], 0xa0);
>> + EXPECT_EQ(bigval[4], 0x00);
>> + EXPECT_EQ(bigval[5], 0x00);
>> + EXPECT_EQ(bigval[6], 0x00);
>> + EXPECT_EQ(bigval[7], 0x0f);
>> +
>> + unsigned char littleval[8] = {0x00};
>> + endian::writeAtBitAlignment<int32_t, little, unaligned>(littleval,
>> + (int)0xffffaaaa, 4);
>> + EXPECT_EQ(littleval[0], 0xa0);
>> + EXPECT_EQ(littleval[1], 0xaa);
>> + EXPECT_EQ(littleval[2], 0xfa);
>> + EXPECT_EQ(littleval[3], 0xff);
>> + EXPECT_EQ(littleval[4], 0x0f);
>> + EXPECT_EQ(littleval[5], 0x00);
>> + EXPECT_EQ(littleval[6], 0x00);
>> + EXPECT_EQ(littleval[7], 0x00);
>> +}
>> +
>> TEST(Endian, Write) {
>> unsigned char data[5];
>> endian::write<int32_t, big, unaligned>(data, -1362446643);
>>
>>
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>
--
Teresa Johnson | Software Engineer | tejohnson at google.com | 408-460-2413
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