Key difference in the out of ld -pie and ld without -pie?

[Tadeus Prastowo]

On Fri, Apr 23, 2021 at 3:03 PM Peng Yu <pengyu.ut@gmail.com> wrote:
>
> On 4/23/21, Tadeus Prastowo <tadeus.prastowo@unitn.it> wrote:
> > I simplified your hello.s and did:
> > $ cat hello.s
> >         .text
> >         .global main
> > main:
> >         lea     s(%rip), %rdi
> >         xor     %rax, %rax
> >         ret
> >         .section        .rodata
> > s:
> >         .string "Hello World!"
> > $ as -c -o hello.o hello.s
> > $ ld -pie hello.o
> > ld: warning: cannot find entry symbol _start; defaulting to
> > 0000000000000221
> >
> > It's just a warning.  I obtained the a.out executable.  Now you can
> > try this on your own and perform further experiments.
>
> It doesn't run. The output should be able to run.
>
> $ ./a.out
> -bash: ./a.out: No such file or directory

Modifying hello.s to use some of your earlier code...
$ cat hello.s
        .global _start
        .text
_start:
        lea     s(%rip), %rdi
        xor     %rax, %rax
        # exit(0)
        mov     $60, %rax               # system call 60 is exit
        xor     %rdi, %rdi              # we want return code 0
        syscall                         # invoke operating system to exit

        .section        .rodata
s:
        .string "Hello World!"
$ as -c -o hello.o hello.s
$ ld -pie -o hello hello.o
$ ./hello
bash: ./hello: No such file or directory
$ readelf -e hello | grep interpreter
      [Requesting program interpreter: /lib/ld64.so.1]
$ ls /lib/ld64.so.1
ls: cannot access '/lib/ld64.so.1': No such file or directory
$ ld  --dynamic-linker /lib64/ld-linux-x86-64.so.2 -pie -o hello hello.o
$ readelf -e hello | grep interpreter
      [Requesting program interpreter: /lib64/ld-linux-x86-64.so.2]
$ ls /lib64/ld-linux-x86-64.so.2
/lib64/ld-linux-x86-64.so.2
$ ./hello; echo $?
0

> --
> Regards,
> Peng

-- 
Best regards,
Tadeus