llvm dev - Aug 2014 - [LLVMdev] possible bug in COFFObjectFile::getSymbolType()

I'm working on adding data detection to llvm-objdump, so it prints out raw
data for symbols with type SymbolRef::ST_Data instead of disassembling them.
This causes llvm/test/MC/ARM/Windows/mov32t-range.s to fail, because the
symbol "truncation" comes back as SymbolRef::ST_Data, and the code
gets
dumped as bytes instead of disassembled.

 

I traced the problem back to COFFObjectFile::getSymbolType() in
llvm/lib/Object/COFFObjectFile.cpp :

    if (Characteristics & COFF::IMAGE_SCN_MEM_READ &&

        ~Characteristics & COFF::IMAGE_SCN_MEM_WRITE) // Read only.

      Result = SymbolRef::ST_Data;

 

I think it should also check for ~Characteristics &
COFF::IMAGE_SCN_MEM_EXECUTE. The symbol, in this case, is READ, EXECUTE,
!WRITE.

 

    if (Characteristics & COFF::IMAGE_SCN_MEM_READ &&

        ~Characteristics & COFF::IMAGE_SCN_MEM_WRITE &&

        ~Characteristics & COFF::IMAGE_SCN_MEM_EXECUTE) // Read only, not
execute.

      Result = SymbolRef::ST_Data;

 

I'm not very familiar with COFF; what ramifications would this change have?

 

Ted

 

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COFF sections also contain stuff like IMAGE_SCN_CNT_CODE and
IMAGE_SCN_CNT_INITIALIZED_DATA.  Are either of those set on the section in
question?

It may make more sense to try to key off of those section characteristics
as well.


On Fri, Aug 22, 2014 at 9:55 AM, Ted Woodward <ted.woodward at
codeaurora.org>
wrote:
> I’m working on adding data detection to llvm-objdump, so it prints out raw
> data for symbols with type SymbolRef::ST_Data instead of disassembling
> them. This causes llvm/test/MC/ARM/Windows/mov32t-range.s to fail, because
> the symbol “truncation” comes back as SymbolRef::ST_Data, and the code gets
> dumped as bytes instead of disassembled.
>
>
>
> I traced the problem back to COFFObjectFile::getSymbolType() in
> llvm/lib/Object/COFFObjectFile.cpp :
>
>     if (Characteristics & COFF::IMAGE_SCN_MEM_READ &&
>
>         ~Characteristics & COFF::IMAGE_SCN_MEM_WRITE) // Read only.
>
>       Result = SymbolRef::ST_Data;
>
>
>
> I think it should also check for ~Characteristics &
> COFF::IMAGE_SCN_MEM_EXECUTE. The symbol, in this case, is READ, EXECUTE,
> !WRITE.
>
>
>
>     if (Characteristics & COFF::IMAGE_SCN_MEM_READ &&
>
>         ~Characteristics & COFF::IMAGE_SCN_MEM_WRITE &&
>
>         ~Characteristics & COFF::IMAGE_SCN_MEM_EXECUTE) // Read only,
not
> execute.
>
>       Result = SymbolRef::ST_Data;
>
>
>
> I’m not very familiar with COFF; what ramifications would this change have?
>
>
>
> Ted
>
>
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
>
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The section is .text, so I assume it’s got IMAGE_SCM_CNT_CODE set. The problem
is the symbol is marked (read & execute), but the test is (read &
!write), so the symbol gets marked as ST_Data instead of ST_Other.

 

From: David Majnemer [mailto:david.majnemer at gmail.com] 
Sent: Friday, August 22, 2014 5:44 PM
To: Ted Woodward
Cc: LLVM Developers Mailing List
Subject: Re: [LLVMdev] possible bug in COFFObjectFile::getSymbolType()

 

COFF sections also contain stuff like IMAGE_SCN_CNT_CODE and
IMAGE_SCN_CNT_INITIALIZED_DATA.  Are either of those set on the section in
question?

 

It may make more sense to try to key off of those section characteristics as
well.

 

On Fri, Aug 22, 2014 at 9:55 AM, Ted Woodward <ted.woodward at
codeaurora.org> wrote:

I’m working on adding data detection to llvm-objdump, so it prints out raw data
for symbols with type SymbolRef::ST_Data instead of disassembling them. This
causes llvm/test/MC/ARM/Windows/mov32t-range.s to fail, because the symbol
“truncation” comes back as SymbolRef::ST_Data, and the code gets dumped as bytes
instead of disassembled.

 

I traced the problem back to COFFObjectFile::getSymbolType() in
llvm/lib/Object/COFFObjectFile.cpp :

    if (Characteristics & COFF::IMAGE_SCN_MEM_READ &&

        ~Characteristics & COFF::IMAGE_SCN_MEM_WRITE) // Read only.

      Result = SymbolRef::ST_Data;

 

I think it should also check for ~Characteristics &
COFF::IMAGE_SCN_MEM_EXECUTE. The symbol, in this case, is READ, EXECUTE, !WRITE.

 

    if (Characteristics & COFF::IMAGE_SCN_MEM_READ &&

        ~Characteristics & COFF::IMAGE_SCN_MEM_WRITE &&

        ~Characteristics & COFF::IMAGE_SCN_MEM_EXECUTE) // Read only, not
execute.

      Result = SymbolRef::ST_Data;

 

I’m not very familiar with COFF; what ramifications would this change have?

 

Ted

 


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