[llvm-dev] Transfer information IR to binary

[Wehrli Johan via llvm-dev]

Thank you for the input.

> But I don't think that's a particularly good solution long term.
> 
> Maybe someone else has a better idea...

Yeah maybe someone else will have an idea :-)

Johan

> 
> --
> Mats
> 
>> How are you dealing with the fact that code gets relocated during loading?
> 
> You talk about the loading phase during the link? If yes, this is why a do the post-processing after the link.
> 
> If you talk about something like the -fpie parameter, I used a small trick.
> 
> The function who will call isModified will calculate the offset dynamically.
> 
> To do this, you get the address in IR (in C++ this is like (uint64_t)std::addressof(main);) and I remove a constant value.
> 
> During the post-processing (again) I will update this constant value with the address into the binary.
> 
> This will give you an offset and you used it to update the addresses.
> 
>> [I'm always curious as to how these type of designs cope with someone modifying the checksumming code itself, but that's another problem - or is this one of these things where the checksum is stored in special hardwareprotected memory?].
> 
> For now, I store it into an special place.
> 
> My first solution for my problem was to used some temporary file but this is highly impractical.
> 
> Maybe I can create a temporary section into the binary but I didn’t find a lot of information about it.
> 
> Thanks,
> 
> Johan
> 
>> --
>> Mats
>> 
>> On 22 February 2016 at 14:45, Wehrli Johan <johan.wehrli at heig-vd.ch <mailto:johan.wehrli at heig-vd.ch>> wrote:
>> I will try to explain better what I do.
>> 
>> The main goal behind this is to verify that a part of code is not modified by someone else (it is an integrity check).
>> 
>> To do this, I create in IR a function who take 2 parameters, a begin and an end value.
>> 
>> This function perform an hash over the code area (from begin to end) and return it.
>> 
>> At first, I don’t know the addresses and the hash value so I put random value (it is an integer 64 bits).
>> 
>> The function look like uint32_t isModified(uint64_t* begin, uint64_t* end).
>> 
>> Once the compilation is over, I need to update the begin address, end address and the hash value.
>> 
>> When I say the compilation is over, I mean the clang driver has finished all of his action (compiling, linking, etc.).
>> 
>> Greetings,
>> 
>> Johan
>> 
>> 
>>> On 22 Feb 2016, at 15:04, mats petersson <mats at planetcatfish.com <mailto:mats at planetcatfish.com>> wrote:
>>> 
>>> What kind of constant: type, value and how is it created?
>>> 
>>> You can make public symbols that you can extract in a linker script to a special section.
>>> 
>>> Or perhaps you want some metadata that a special late state (machine instr) pass is extracting and adding.
>>> 
>>> The "best" solution really depends on what you are trying to achieve overall and what kind of data you are working with.
>>> 
>>> --
>>> Mats
>>> 
>>> On 22 February 2016 at 13:04, Wehrli Johan via llvm-dev <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
>>> Hi,
>>> 
>>> I want to know if it is possible to pass information from IR to the final binary (like a constant value)?
>>> 
>>> I have a module pass in IR who make some transformation and, once the compilation is finished, I need to apply a post-processing.
>>> 
>>> The post-processing need information from the IR part.
>>> 
>>> Greetings,
>>> 
>>> Johan
>>> 
>>> 
>>> 
>>> _______________________________________________
>>> LLVM Developers mailing list
>>> llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>
>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev <http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev>
>>> 
>>> 
>> 
>> 
> 
> 

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20160223/9aadd020/attachment.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 842 bytes
Desc: Message signed with OpenPGP using GPGMail
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20160223/9aadd020/attachment.sig>