gcc now producing position indepent code?

[rplantz]

I have a simple Hello world C program that uses write:



#include <unistd.h>
int main(void)
{

write(STDOUT_FILENO, "Hello world.\n", 13);

return 0;
}

When I last compiled it (5 years ago) it produced:



.file "helloWorld2.c"
.section .rodata
.LC0:
.string "Hello world.\n" # constant data
.text
.globl main
.type main, @function
main:
pushq %rbp
movq %rsp, %rbp
movl $13, %edx # third argument
movl $.LC0, %esi # second argument
movl $1, %edi # first argument
call write
movl $0, %eax
popq %rbp
ret
.size main, .-main
.ident "GCC: (Ubuntu/Linaro 4.7.0-7ubuntu3) 4.7.0"
.section .note.GNU-stack,"",@progbits


Now it produces:



.file "helloWorld2.c"
.section .rodata
.LC0:
.string "Hello world.\n"
.text
.globl main
.type main, @function
main:
.LFB0:
.cfi_startproc
pushq %rbp
.cfi_def_cfa_offset 16
.cfi_offset 6, -16
movq %rsp, %rbp
.cfi_def_cfa_register 6
movl $13, %edx
leaq .LC0(%rip), %rsi
movl $1, %edi
call write@PLT
movl $0, %eax
popq %rbp
.cfi_def_cfa 7, 8
ret
.cfi_endproc
.LFE0:
.size main, .-main
.ident "GCC: (Ubuntu 7.2.0-8ubuntu3.2) 7.2.0"
.section .note.GNU-stack,"",@progbits

When did gcc start producing PIC?

[&wP*!)]

Which GCC versions did you use in both cases?
And which options were given to each compiler?
Was it a cross compilation?

[rplantz]

Which GCC versions did you use in both cases?
The older compilation used gcc 4.7.0, the newer one 7.2.0. I'm not positive about the date of the older one, but it was 3 - 5 years ago.

And which options were given to each compiler?
-S to get the assembly language and -O0 for no optimization. I may have also used -g to get debugging symbols.

Was it a cross compilation? No.

I have read elsewhere that Ubuntu started using Address Space Layout Randomization (ASLR) with the 16.10 release. If I'm understanding things correctly, that means that the default became position independent code.

[&wP*!)]

To find out whether your GCC compiler also has this default setting, type: gcc -v and search whether the option --enable-default-pie is there. If this option is in the stderr of gcc -v, then yes, all your object files coming from gcc -o <object file> are position-independent code.

I confirm what you say: because of ASLR (security reasons) almost all OSes have GCC with PIC enabled.