[llvm] r263378 - [CodeView] Truncate display names

[David Blaikie via llvm-commits]

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?)


>
> 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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