[LLVMdev] llvm-objdump related patch

Neo smtian at ingenic.cn
Tue Oct 11 20:41:34 PDT 2011

On 2011年10月12日 03:40, Michael Spencer wrote:
> On Tue, Oct 11, 2011 at 12:15 AM, Neo<smtian at ingenic.cn>  wrote:
>> Hi,
>>     I am new to llvm, not familiar with c++, after some use with
>> llvm-objdump, and finding the broken output, I try to debug and fix the code
>> so it can become usable. Please help review the patch, so that they can be
>> merged.
>>     And there's still two major problem I have found about arm disassembler:
>> 1. arm instruction decoder cannot recognise bx series instructions.
>> 2. As gcc will generate thumb and arm instruction mixed binary, we have to
>> switch from each other.
>> we can tell if a function is thumb or arm code by looking at the symbol
>> table entry, when in thumb code, the lowest bit of the symbol value will be
>> set to '1'.
>> so how these logic can be implemented while still adapt to the structure of
>> the code?
>> Songmao
> For the first patch. The code is only valid for executable files, not
> relocatable files. st_shndx should be used to determine if the symbol
> is in the given section. Also st_value can hold the offset into
> st_shndx, not the actual address. Also it doesn't handle non-function
> symbols.
> For the second patch. Could you explain what exactly you are trying to
> fix? I see some stuff that I know is wrong, but it would help if I
> knew the intent. As for what I do know.
> * The error function already prints out the error. If you want to
> print additional info, add an overload of error that allows that.
> * Please use spaces instead of tabs. Lots of the code doesn't line up
> properly for me.
> * Setting the size to 4 to skip bytes is arbitrary, and won't always
> give decent results on different platforms.
> Thank you for working on this.
> As for your comments on the arm disassembler.
> 1) I am not familiar with ARM, but I do know the decoder is currently
> being worked on.
> 2) We were just discussing this in IRC. The idea is to simply handle
> ARM disassembly as a special case and inspect the bit to decide how to
> disassemble the symbol.
> - Michael Spencer
I have just found out that arm disassembler use tblgen -gen-disassembler 
not -gen-arm-decoder, so I have looked at the wrong code, but can anyone 
explain what the arm-decoder is for?
The llvm-objdump failed on bx lr insn(0xe12fff1e),because the 
condition(Bits & ARM::HasV4TOps) has failed, the Bits is 0, so it 
failed, but I haven't found out why.


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