[compiler-rt] r277558 - Reduce coverage PC buffer size on 32-bit Windows to match 32-bit Linux

[Kostya Serebryany via llvm-commits]

These are serving different purposes.
pc_array is the array of PCs indexed by the PC index (PC indices are
computed at the process start up).
It's needed for the core coverage functionality.

pc_buffer accumulates PCs in the order they appear, which is a useful
signal for libFuzzer, but probably not useful for anything else.
Mike, I think we should make it "less default" than it's now.

Reid, I guess for now you can use coverage_pc_buffer=0

--kcc




On Wed, Aug 3, 2016 at 9:10 AM, Reid Kleckner <rnk at google.com> wrote:

> This still isn't enough space for Chrome apparently:
>
> C:\src\chromium\src\out\asan>chrome
> [0803/085325:ERROR:file_io.cc(30)] read: expected 4, observed 0
> ==7920==AddressSanitizer CHECK failed:
> ..\projects\compiler-rt\lib\sanitizer_common\sanitizer_coverage_libcdep.cc:429
> "((idx * sizeof(uptr))) < ((atomic_load(&pc_array_size,
> memory_order_acquire)))" (0x40256bc, 0x4000000)
>     #0 0x68cd64a7 in __asan::AsanCheckFailed
> c:\src\llvm\projects\compiler-rt\lib\asan\asan_rtl.cc:68
>     #1 0x68cb7a43 in __sanitizer::CheckFailed
> c:\src\llvm\projects\compiler-rt\lib\sanitizer_common\sanitizer_termination.cc:79
>     #2 0x68cb8077 in __sanitizer::CoverageData::Add
> c:\src\llvm\projects\compiler-rt\lib\sanitizer_common\sanitizer_coverage_libcdep.cc:428
>     #3 0x68cbae54 in __sanitizer_cov
> c:\src\llvm\projects\compiler-rt\lib\sanitizer_common\sanitizer_coverage_libcdep.cc:947
>     #4 0x57eda1f9 in _GLOBAL__sub_I_cld2_generated_quadchrome_2.cc
> C:\src\chromium\src\third_party\cld_2\src\internal\cld2_generated_quadchrome_2.cc
>
> Why do we need two of these kPcArrayMaxSize buffers? First we do this:
>   pc_array = reinterpret_cast<uptr *>(
>       MmapNoReserveOrDie(sizeof(uptr) * kPcArrayMaxSize, "CovInit"));
>
> And later this:
>   if (common_flags()->coverage_pc_buffer)
>     pc_buffer = reinterpret_cast<uptr *>(MmapNoReserveOrDie(
>         sizeof(uptr) * kPcArrayMaxSize, "CovInit::pc_buffer"));
>
> On Tue, Aug 2, 2016 at 6:19 PM, Reid Kleckner via llvm-commits <
> llvm-commits at lists.llvm.org> wrote:
>
>> Author: rnk
>> Date: Tue Aug  2 20:19:46 2016
>> New Revision: 277558
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=277558&view=rev
>> Log:
>> Reduce coverage PC buffer size on 32-bit Windows to match 32-bit Linux
>>
>> In r235779, Timur bumped the buffer size up to 1<<27, or about 134
>> million coverage points, presumably to handle Chrome. We allocate two
>> arrays of uptrs with this size, and this reliably exhausts all available
>> address space on 32-bit Windows (2 allocations of 512MB) when ASan is
>> also enabled.
>>
>> Let's reduce the buffer size for now to stabilize the test suite. We can
>> re-evaluate the approach later when we've brought the Chrome ASan
>> builders back to life.
>>
>> Kostya said that Mike reduced the number of instrumented coverage points
>> that LLVM emits by half since Timur made this change, so reducing this
>> array size should also be safe.
>>
>> With this change, the 32-bit ASan tests reliably pass for me on Windows
>> 10.
>>
>> Modified:
>>     compiler-rt/trunk/lib/sanitizer_common/sanitizer_coverage_libcdep.cc
>>
>> Modified:
>> compiler-rt/trunk/lib/sanitizer_common/sanitizer_coverage_libcdep.cc
>> URL:
>> http://llvm.org/viewvc/llvm-project/compiler-rt/trunk/lib/sanitizer_common/sanitizer_coverage_libcdep.cc?rev=277558&r1=277557&r2=277558&view=diff
>>
>> ==============================================================================
>> --- compiler-rt/trunk/lib/sanitizer_common/sanitizer_coverage_libcdep.cc
>> (original)
>> +++ compiler-rt/trunk/lib/sanitizer_common/sanitizer_coverage_libcdep.cc
>> Tue Aug  2 20:19:46 2016
>> @@ -125,9 +125,8 @@ class CoverageData {
>>
>>    // Maximal size pc array may ever grow.
>>    // We MmapNoReserve this space to ensure that the array is contiguous.
>> -  static const uptr kPcArrayMaxSize = FIRST_32_SECOND_64(
>> -      1 << (SANITIZER_ANDROID ? 24 : (SANITIZER_WINDOWS ? 27 : 26)),
>> -      1 << 27);
>> +  static const uptr kPcArrayMaxSize =
>> +      FIRST_32_SECOND_64(1 << (SANITIZER_ANDROID ? 24 : 26), 1 << 27);
>>    // The amount file mapping for the pc array is grown by.
>>    static const uptr kPcArrayMmapSize = 64 * 1024;
>>
>>
>>
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>
>
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