x86 ISA Program

So, you want to talk about performance.

x86 ISA Program

• MASM, the Microsoft Assembler. It outputs OMF files (but Microsoft’s linker can convert them to win32 format). It supports a massive and clunky assembly language. Memory addressing is not intuitive. The directives required to set up a program make programming unpleasant.

• GAS, the GNU assember. This uses the rather ugly AT&T-style syntax so many people do not like it; however, you can configure it to use and understand the Intel-style. It was designed to be part of the back end of the GNU compiler collection (gcc).

• NASM, the "Netwide Assembler." It is free, small, and best of all it can output zillions of different types of object files. The language is much more sensible than MASM in many respects.

Command

gcc hello.s -nostdlib -no-pie

Position Independent Executables (PIE) are an output of the hardened package build process. A PIE binary and all of its dependencies are loaded into random locations within virtual memory each time the application is executed. This makes Return Oriented Programming (ROP) attacks much more difficult to execute reliably. These blog posts are designed to showcase the results of a study I did recently which looked at the effect of building applications using PIE. In the study I investigated the overhead incurred in the loader during program startup with the aim to help distributions make better security decisions based on a technical analysis. The focus on program startup was chiefly to examine the place where PIE has the largest performance impact. The performance post process execution is largely comparable to standard Dynamic Shared Objects (DSOs) on x86_64 machines depending on how well the program and shared libraries have been designed.

Hello World

GCC hello.c to hello.s

        .file   "hello.c"
        .text
        .section        .rodata
.LC0:
        .string "Hello, world\n"
        .text
        .globl  main
        .type   main, @function
main:
.LFB0:
        .cfi_startproc
        endbr64
        pushq   %rbp
        .cfi_def_cfa_offset 16
        .cfi_offset 6, -16
        movq    %rsp, %rbp
        .cfi_def_cfa_register 6
        leaq    .LC0(%rip), %rdi
        movl    $0, %eax
        call    printf@PLT
        movl    $0, %eax
        popq    %rbp
        .cfi_def_cfa 7, 8
        ret
        .cfi_endproc
.LFE0:
        .size   main, .-main
        .ident  "GCC: (Ubuntu 9.4.0-1ubuntu1~20.04.1) 9.4.0"
        .section        .note.GNU-stack,"",@progbits
        .section        .note.gnu.property,"a"
        .align 8
        .long    1f - 0f
        .long    4f - 1f
        .long    5
0:
        .string  "GNU"
1:
        .align 8
        .long    0xc0000002
        .long    3f - 2f
2:
        .long    0x3
3:
        .align 8
4:

x86 hello.s

        .global _start

        .text
_start:
        # write(1, message, 13)
        mov     $1, %rax                # system call 1 is write
        mov     $1, %rdi                # file handle 1 is stdout
        mov     $message, %rsi          # address of string to output
        mov     $13, %rdx               # number of bytes
        syscall                         # invoke operating system to do the write

        # exit(0)
        mov     $60, %rax               # system call 60 is exit
        xor     %rdi, %rdi              # we want return code 0
        syscall                         # invoke operating system to exit
message:
        .ascii  "Hello, world\n"

Benchmark

GCC

Hello, world

real    0m0.001s
user    0m0.001s
sys     0m0.000s

x86

Hello, world

real    0m0.000s
user    0m0.000s
sys     0m0.000s

Reference

https://cs.lmu.edu/~ray/notes/x86assembly/