[lldb-dev] Identifying instructions that definitely access memory

[Vangelis Tsiatsianas via lldb-dev]

Hi Tatyana,

Thank you for your reply! 🙂

If I understand correctly, TargetOpcode::G_{LOAD, STORE} do not cover x86’s mov instructions (and other relevant instructions of both x86 the rest of supported architectures) and such, which also access memory, however I will look into it more.

Additionally, thank you for the suggestion regarding llvm-dev ―I will forward my email to that list, too.


― Vangelis


> On 7 Nov 2019, at 13:49, Tatyana Krasnukha <Tatyana.Krasnukha at synopsys.com> wrote:
> 
> Hi Vangelis,
>  
> Not sure this will help you, but you can try to compare llvm::MachineInstr::getOpcode() with TargetOpcode::G_LOAD and TargetOpcode::G_STORE if you can obtain a MachineInstr instance.
> It also may have sense to ask llvm-dev for a proper solution.
>  
> From: lldb-dev <lldb-dev-bounces at lists.llvm.org> On Behalf Of Vangelis Tsiatsianas via lldb-dev
> Sent: Tuesday, November 5, 2019 3:43 PM
> To: via lldb-dev <lldb-dev at lists.llvm.org>
> Cc: Vangelis Tsiatsianas <vangelists at icloud.com>
> Subject: Re: [lldb-dev] Identifying instructions that definitely access memory
>  
> Hello,
>  
> I decided to try once more with a follow-up email, since my previous one got no responses (I hope it’s not considered rude to send more than one message in a row for a particular question).
>  
> To sum up and clarify my previous question, what I need is a way to track memory stores and save both the old and the new value of the memory location being modified.
>  
> My thinking so far:
> Recognize the instructions that definitely access memory before they execute, based on their opcode.
> Tell whether each operand is a register or a memory location.
> If it’s a memory location, check whether it is a load or store destination.
> In case it is a store destination, fetch and save current value from memory.
> Execute instruction.
> Fetch and save new value from memory.
>  
> However, I was not able to find a cross-architecture API that covers all of the conditions above and more specifically Instruction::DoesStore() and Operand::IsStoreDestination().
>  
> Last but not least, I should notice that the target is executed in single-step mode, so I do have control right before and after the execution of every instruction.
>  
> Thanks, again, in advance! 🙂
>  
>  
> ― Vangelis
>  
> 
> 
> On 21 Oct 2019, at 08:54, Vangelis Tsiatsianas <vangelists at icloud.com <mailto:vangelists at icloud.com>> wrote:
>  
> Hello,
>  
> I am looking for a way to identify loads, stores and any other kind of instruction that definitely perform memory access and extract the address operand(s), however I was not able to find a cross-architecture API. The closest I stumbled upon are "MCInstrDesc::mayLoad()" and "MCInstrDesc::mayStore()", but I understand that their results are just a hint, so I would then need to examine the instruction name or opcode in order to find out whether it’s actually a load or store and which operand(s) is (are) memory address(es) and also do so for each architecture separately, which I would really like to avoid.
>  
> Is there a way to identify such instructions either by examining them through the disassembler (e.g. "DoesLoad()" | "DoesStore()") before they execute or right after they perform any kind of memory access?
>  
> Thank you very much, in advance! 🙂
>  
>  
> ― Vangelis

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