Re: [patch] disassembly window

[Andrew Cagney <cagney@redhat.com>]

Zhao Shujing wrote:
> Hi, Andrew
> Thanks for the explanation of disassemble backwards.
>
> If the symbol isn't available, gdb's disassemble command would return
> "No function contains specified address". Would frysk's disassemble
> command disassemble a small range from the frame's PC, not just return
> some warning sentence?
>   
Pearly,

yes, the command-line will still disassemble.  And I like the idea of 
the disassembler-window can do something similar.

Andrew

> Thanks
> Pearly
> On Mon, 2007-08-20 at 09:32 -0400, Andrew Cagney wrote:
>   
>> Zhao Shujing wrote:
>>     
>>> Hi
>>>
>>> This patch is to fix bug #4932 and other bugs of disassembly window. 
>>> rowPrepend is added to prepend rows by calculating memory information
>>> like rowAppend. Because the methods that are provided by class
>>> Disassembler, disassembleInstructions and
>>> disassembleInstructionsStartEnd, can only read the instructions that are
>>> following some address, rowPrepend have to use two while execution
>>> control to read the instructions that are preceding some address.
>>> Any suggestions are welcomed.
>>>   
>>>       
>> Pearly, nice work.
>>
>> The challenge here, and the reason why the disassembler only goes 
>> forward from PC is that, in general, it isn't possible to disassemble 
>> backwards.  This is because architectures such as the i386 and x86-64 
>> have variable length instructions making it effectively impossible to 
>> figure out where, looking backwards, an instruction starts.  For 
>> instance, looking backwards is that a one byte int80 instruction, or a 
>> multi-byte instruction loading the hex code for int80?
>>
>> For disassembling a range, can I suggest doing something similar to the 
>> disassembler command in frysk.hpd.DisassemblerCommand.  That code first 
>> attempts to fetch the frysk.symtab.Symbol at the frame's 
>> adjusted-address and then uses its address/size to determine the start 
>> address and size to disassemble.  If the symbol isn't available, then 
>> I'd just disassemble a small range from the frame's PC.
>>
>> One heads up for you; you may want to consider configuring your personal 
>> build with --with-libopcodes.
>>
>> Andrew
>>
>>     
>
>
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