[llvm] r263378 - [CodeView] Truncate display names

[David Majnemer via llvm-commits]

On Sun, Mar 13, 2016 at 12:51 PM, David Blaikie <dblaikie at gmail.com> wrote:

>
>
> On Sun, Mar 13, 2016 at 3:53 AM, David Majnemer via llvm-commits <
> llvm-commits at lists.llvm.org> wrote:
>
>> Author: majnemer
>> Date: Sun Mar 13 05:53:30 2016
>> New Revision: 263378
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=263378&view=rev
>> Log:
>> [CodeView] Truncate display names
>>
>> Fundamentally, the length of a variable or function name is bound by the
>> maximum size of a record: 0xffff.  However, the name doesn't live in a
>> vacuum; other data is associated with the name, lowering the bound
>> further.
>>
>> We would naively attempt to emit the name, causing us to assert because
>> the record would no-longer fit in 16-bits.  Instead, truncate the name
>> but preserve as much as we can.
>>
>> While I have tested this locally, I've decided to not commit it due to
>> the test's size.
>>
>
> ^ Did you change your mind? or unintentionally commit it? (or am I
> misunderstanding this comment?)
>

I believe there is a misunderstanding here.  I decided to omit the test due
to it's size.


>
>
>>
>> N.B.  While this behavior is undesirable, it is better than MSVC's
>> behavior.  They seem to truncate to ~4000 characters.
>>
>> Modified:
>>     llvm/trunk/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
>>
>> Modified: llvm/trunk/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp?rev=263378&r1=263377&r2=263378&view=diff
>>
>> ==============================================================================
>> --- llvm/trunk/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp (original)
>> +++ llvm/trunk/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp Sun Mar 13
>> 05:53:30 2016
>> @@ -397,10 +397,11 @@ void CodeViewDebug::emitInlinedCallSite(
>>    OS.EmitIntValue(SymbolRecordKind::S_INLINESITE_END, 2); // RecordKind
>>  }
>>
>> -static void emitNullTerminatedString(MCStreamer &OS, StringRef S) {
>> +static void emitNullTerminatedString(MCStreamer &OS, StringRef S,
>> +                                     size_t MaxSize) {
>> +  S = S.substr(0, MaxSize);
>>    SmallString<32> NullTerminatedString(S);
>> -  if (NullTerminatedString.empty() || NullTerminatedString.back() !=
>> '\0')
>> -    NullTerminatedString.push_back('\0');
>> +  NullTerminatedString.push_back('\0');
>>    OS.EmitBytes(NullTerminatedString);
>>  }
>>
>> @@ -462,7 +463,8 @@ void CodeViewDebug::emitDebugInfoForFunc
>>      OS.EmitIntValue(0, 1);
>>      // Emit the function display name as a null-terminated string.
>>      OS.AddComment("Function name");
>> -    emitNullTerminatedString(OS, FuncName);
>> +    // Truncate the name so we won't overflow the record length field.
>> +    emitNullTerminatedString(OS, FuncName, 0xffd9);
>>      OS.EmitLabel(ProcRecordEnd);
>>
>>      for (const LocalVariable &Var : FI.Locals)
>> @@ -706,7 +708,8 @@ void CodeViewDebug::emitLocalVariable(co
>>    OS.EmitIntValue(TypeIndex::Int32().getIndex(), 4);
>>    OS.AddComment("Flags");
>>    OS.EmitIntValue(Flags, 2);
>> -  emitNullTerminatedString(OS, Var.DIVar->getName());
>> +  // Truncate the name so we won't overflow the record length field.
>> +  emitNullTerminatedString(OS, Var.DIVar->getName(), 0xfff6);
>>    OS.EmitLabel(LocalEnd);
>>
>>    // Calculate the on disk prefix of the appropriate def range record.
>> The
>>
>>
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>
>
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