[lldb-dev] Identifying instructions that definitely access memory

Vangelis Tsiatsianas via lldb-dev lldb-dev at lists.llvm.org
Tue Nov 5 04:43:29 PST 2019


I decided to try once more with a follow-up email, since my previous one got no responses (I hope itโ€™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 itโ€™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! ๐Ÿ™‚

โ€• Vangelis

> On 21 Oct 2019, at 08:54, Vangelis Tsiatsianas <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 itโ€™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! ๐Ÿ™‚
> โ€• Vangelis

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