Re: [Valgrind-users] Execution Manipulation using valgrind

[WAROQUIERS P. <phi...@eu...>]

memcheck at least is instrumenting other/all instructions.
For example, to keep track of uninitialised bits, it has to instrument
an Add32 expression which
would make an addition between something initialised and something not
initialised.
 
Philippe
 

 

________________________________

	From: Vinay Chippa [mailto:vin...@gm...] 
	Sent: Thursday 19 January 2012 13:28
	To: WAROQUIERS Philippe
	Cc: val...@li...
	Subject: Re: [Valgrind-users] Execution Manipulation using
valgrind
	
	
	Hi,  
	         Thanks for the quick reply. I think I get what you
mean. I have been going through the lackey tool code. And it seems like
the tool takes a code superblock (SB) as input and outputs a different
superblock. And all these tools (lackey, cachegrind, memcheck etc.,) are
trying to keep the output SB same as input SB. This answers my basic
question and I think I can use Valgrind for my requirement.
	         I have one more question. Most of these tools (lackey,
memcheck, cachegrind etc.,) are instrumenting memory related
instructions. Are there any popular tools that instrument other/all
instructions (add, mul etc.,)?.

	Thanks,
	Vinay.         
	            
	
	
	On Thu, Jan 19, 2012 at 6:52 AM, WAROQUIERS Philippe
<phi...@eu...> wrote:
	

		
		All the Valgrind tools (except the "none" tool) are
doing code manipulation.
		 
		These Valgrind tools are only "augmenting" the code,
trying hard to not change
		the semantic of the code (e.g. memcheck instruments the
code to see if
		 uninitialised values are used, helgrind instruments the
code to detect race condition, etc ...).
		 
		But you can for sure write a tool which modifies the
semantic of the code.
		For example, if the tool gets an IR expression "Add32"
(means: an addition of two values), the tool
		instrumentation function might transform this into a
"Mul32", thereby injecting a fault).
		 
		Philippe
		 


________________________________

			From: Vinay Chippa [mailto:vin...@gm...]

			Sent: Thursday 19 January 2012 12:39
			To: val...@li...
			Subject: [Valgrind-users] Execution Manipulation
using valgrind
			
			
			Hi all, 
			          I have a basic question regarding the
capabilities of Valgrind. I am looking for ways to manipulate the
execution of a given software (mostly by changing the values of
instruction operands). I would like to develop a valgrind tool that goes
through each instruction (or a subset of instructions) of the software,
changes the values of the operands and executes the software with the
modified operands.
			          From the valgrind documentation and
the list of standard tools (memcheck, cachegrind etc.,), I felt that the
executing code was just being monitored/observed but not modified.
However, the wiki link of valgrind clearly states that the execution can
be manipulated
			
			*Valgrind first translates the program into a
temporary, simpler form called Intermediate Representation (IR), which
is a processor-neutral, SSA-based form. After the conversion, a tool
(see below) is free to do whatever transformations it would like on the
IR, before Valgrind translates the IR back into machine code and lets
the host processor run it. *
			
			I also looked through the discussion archives
and found that there were some patches related to fault injection but I
was unable to infer anything from those mails. 
			           I would be glad if someone can
provide information on the capabilities of valgrind in regards to code
manipulation and if possible, give some pointers to existing tools that
employ these capabilities. 
			
			Thanks,
			Vinay. 



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