Re: [RFC/RFT,V2] CFI: Add support for gcc CFI in aarch64

["Wang" <wanglikun@lixiang.com>]

[-- Attachment #1: Type: text/plain, Size: 2553 bytes --]

On 2023/12/13 16:48, Dan Li wrote:
> + Likun
>
> On Tue, 28 Mar 2023 at 06:18, Sami Tolvanen <samitolvanen@google.com> wrote:
>> On Mon, Mar 27, 2023 at 2:30 AM Peter Zijlstra <peterz@infradead.org> wrote:
>>> On Sat, Mar 25, 2023 at 01:54:16AM -0700, Dan Li wrote:
>>>
>>>> In the compiler part[4], most of the content is the same as Sami's
>>>> implementation[3], except for some minor differences, mainly including:
>>>>
>>>> 1. The function typeid is calculated differently and it is difficult
>>>> to be consistent.
>>> This means there is an effective ABI break between the compilers, which
>>> is sad :-( Is there really nothing to be done about this?
>> I agree, this would be unfortunate, and would also be a compatibility
>> issue with rustc where there's ongoing work to support
>> clang-compatible CFI type hashes:
>>
>> https://github.com/rust-lang/rust/pull/105452
>>
>> Sami


Hi Peter and Sami

I am Dan Li's colleague, and I will take over and continue the work of CFI.

Regarding the issue of gcc cfi type id being compatible with clang, we 
have analyzed and verified:

1. clang uses Mangling defined in Itanium C++ ABI to encode the function 
prototype, and uses the encoding result as input to generate cfi type id;
2. Currently, gcc only implements mangling for the C++ compiler, and the 
function prototype coding generated by these interfaces is compatible 
with clang, but gcc's c compiler does not support mangling.;

Adding mangling to gcc's c compiler is a huge and difficult task，because 
we have to refactor the mangling of C++, splitting it into basic 
mangling and language specific mangling, and adding support for the c 
language which requires a deep understanding of the compiler and 
language processing parts.

And for the kernel cfi, I suggest separating type compatibility from CFI 
basic functions. Type compatibility is independent from CFI basic 
funcitons and should be dealt with under another topic. Should we focus 
on the main issus of cfi, and  let it work first on linux kernel, and 
left the compatible issue to be solved later?

LiKun Wang

声明：这封邮件只允许文件接收者阅读，有很高的机密性要求。禁止其他人使用、打开、复制或转发里面的任何内容。如果本邮件错误地发给了你，请联系邮件发出者并删除这个文件。机密及法律的特权并不因为误发邮件而放弃或丧失。任何提出的观点或意见只属于作者的个人见解，并不一定代表本公司。