[llvm-dev] What's definition to type of function in -fsanitize=cfi-icall in llvm/clang 7? (original) (raw)

PenYiWang via llvm-dev llvm-dev at lists.llvm.org
Thu Jan 24 17:30:20 PST 2019

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)?

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