[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 17:00:47 PDT 2015
How do I get UBSan to run on the unittests? I don't see where the
option is being added on the buildbot page, but maybe I missed it.
Thanks,
Teresa
On Wed, Oct 7, 2015 at 4:18 PM, Teresa Johnson <tejohnson at google.com> wrote:
> 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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>>> llvm-commits at lists.llvm.org
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>>
>
>
>
> --
> Teresa Johnson | Software Engineer | tejohnson at google.com | 408-460-2413
--
Teresa Johnson | Software Engineer | tejohnson at google.com | 408-460-2413
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