llvm dev - Jan 2019 - What's definition to type of function in -fsanitize=cfi-icall in llvm/clang 7?

Hi

I learn llvm/clang cfi from this repo and also the usenix '14 paper.
https://github.com/trailofbits/clang-cfi-showcase/blob/master/cfi_icall.c

As usenix '14 paper says, the type of functoin is determined only by number
of argument.

But I try in llvm/clang 7, I found that it is getting complicated.

For example,

#include<stdio.h>

int func(int a,float b,char c){
  printf("hi %d,%f,%c\n",a,b,c);
  return a+1;
}

int main(){
  int (*fp)(int,float,char);
  fp = func;
  fp(1,1.0,'c');

  return 0;
}

clang -flto -fsanitize=cfi -fvisibility=hidden -O0 ./test.c

And the use objdump to see the executable :

00000000004005a0 <__typeid__ZTSFiifcE_global_addr>:
  4005a0:       e9 4b ff ff ff          jmpq   4004f0 <func.cfi>
  4005a5:       cc                      int3
  4005a6:       cc                      int3
  4005a7:       cc                      int3
  4005a8:       0f 1f 84 00 00 00 00    nopl   0x0(%rax,%rax,1)
  4005af:       00
>From the type id mangling "iifc", I can guess that the type of
return value
and the type of every argument are the factors to determine the type of a
function.

I wonder that what's the definition of type of a function in llvm/clang 7.

Is there any document I can study?

Or I should study the code in compiler fronted (clang)?

Thank you.
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+Peter Collingbourne <pcc at google.com>

On Thu, Jan 24, 2019 at 5:30 PM PenYiWang via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> Hi
>
> I learn llvm/clang cfi from this repo and also the usenix '14 paper.
> https://github.com/trailofbits/clang-cfi-showcase/blob/master/cfi_icall.c
>
> As usenix '14 paper says, the type of functoin is determined only by
> number of argument.
>
> But I try in llvm/clang 7, I found that it is getting complicated.
>
> For example,
>
> #include<stdio.h>
>
> int func(int a,float b,char c){
>   printf("hi %d,%f,%c\n",a,b,c);
>   return a+1;
> }
>
> int main(){
>   int (*fp)(int,float,char);
>   fp = func;
>   fp(1,1.0,'c');
>
>   return 0;
> }
>
> clang -flto -fsanitize=cfi -fvisibility=hidden -O0 ./test.c
>
> And the use objdump to see the executable :
>
> 00000000004005a0 <__typeid__ZTSFiifcE_global_addr>:
>   4005a0:       e9 4b ff ff ff          jmpq   4004f0 <func.cfi>
>   4005a5:       cc                      int3
>   4005a6:       cc                      int3
>   4005a7:       cc                      int3
>   4005a8:       0f 1f 84 00 00 00 00    nopl   0x0(%rax,%rax,1)
>   4005af:       00
>
> From the type id mangling "iifc", I can guess that the type of
return
> value and the type of every argument are the factors to determine the type
> of a function.
>
> I wonder that what's the definition of type of a function in llvm/clang
7.
>
> Is there any document I can study?
>
> Or I should study the code in compiler fronted (clang)?
>
> Thank you.
>
>
>
>
>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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