Re: [patch] disassembly window

[Zhao Shujing <pearly dot zhao at oracle dot com>]

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?

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
>