CODEWITHSUNDEEP
cgccclang
Zhongkun Ma
Zhongkun Ma

Reputation: 429

Clang does not accept -shared -fPIC -pie compiler flags simultaneously

Given by below code:

#include <stdio.h>

void output()
{
  printf("hello \n");
}

int main()
{
  output();
  return 0;
}

When the above code is compiled by below command:

gcc hello.c -shared -fPIC -pie -o libhello.so -Wl,-E

The generated libhello.so is not only a shared lib, but also an executable. However, when change gcc to clang as below 

clang-10 hello.c -shared -fPIC -pie -o libhello.so -Wl,-E

The compilation gives below warning:

clang: warning: argument unused during compilation: '-pie' [-Wunused-command-line-argument]

When executing libhello.so compiled by clang-10, it also crashed.

Question: 1. Is it possible to use clang compile runnable shared lib as gcc?

Note : This question is asked only for my own curiosity and I am not facing any practical problem.

Upvotes: 1

Views: 2094

Answers (1)

Zhongkun Ma
Zhongkun Ma

Reputation: 429

As warning by the clang-10, clang-10 does not generate below things as GCC compilers:

  1. INTERP segment in shared lib's program header
  2. _start() function

Both of them can be manually as below 

#include <stdio.h>

const char interp_section[] __attribute__((section(".interp"))) = "/lib64/ld-linux-x86-64.so.2";

void output()
{
  printf("hello \n");
}

int main()
{
  output();
  return 0;
}

void _start()
{
  printf("hello.c : %s\n", __FUNCTION__);
  exit(0);
}

However, it's better to use -Wl,-e,YourEntryFunction flags to create shared object runnable instead of the approach presented in the above question.

Upvotes: 0

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