我想知道从程序的入口点返回ret是否合法。

NASM的示例:

section .text
global _start
_start:
ret

; Linux: nasm -f elf64 foo.asm -o foo.o && ld foo.o
; OS X:  nasm -f macho64 foo.asm -o foo.o && ld foo.o -lc -macosx_version_min 10.12.0 -e _start -o foo

最佳答案

MacOS动态可执行文件

当您使用和MacOS 并链接到:

ld foo.o -lc -macosx_version_min 10.12.0 -e _start -o foo

A Mach-O executable file contains a header consisting of a set of load commands. For programs that use shared libraries or frameworks, one of these commands specifies the location of the linker to be used to load the program. If you use Xcode, this is always /usr/lib/dyld, the standard OS X dynamic linker.

When you call the execve routine, the kernel first loads the specified program file and examines the mach_header structure at the start of the file. The kernel verifies that the file appear to be a valid Mach-O file and interprets the load commands stored in the header. The kernel then loads the dynamic linker specified by the load commands into memory and executes the dynamic linker on the program file.

The dynamic linker loads all the shared libraries that the main program links against (the dependent libraries) and binds enough of the symbols to start the program. It then calls the entry point function. At build time, the static linker adds the standard entry point function to the main executable file from the object file /usr/lib/crt1.o. This function sets up the runtime environment state for the kernel and calls static initializers for C++ objects, initializes the Objective-C runtime, and then calls the program’s main function

start address 0x0000000000000000

Sections:
Idx Name          Size      VMA               LMA               File off  Algn
  0 .text         00000001  0000000000001fff  0000000000001fff  00000fff  2**0
                  CONTENTS, ALLOC, LOAD, CODE
SYMBOL TABLE:
0000000000001000 g       03 ABS    01 0010 __mh_execute_header
0000000000001fff g       0f SECT   01 0000 [.text] _start
0000000000000000 g       01 UND    00 0100 dyld_stub_binder

Disassembly of section .text:

0000000000001fff <_start>:
    1fff:       c3                      retq

For programs that use shared libraries or frameworks, one of these commands specifies the location of the linker to be used to load the program.

ld foo.o -macosx_version_min 10.12.0 -e _start -o foo -static

start address 0x0000000000001fff

Sections:
Idx Name          Size      VMA               LMA               File off  Algn
  0 .text         00000001  0000000000001fff  0000000000001fff  00000fff  2**0
                  CONTENTS, ALLOC, LOAD, CODE
  1 LC_THREAD.x86_THREAD_STATE64.0 000000a8  0000000000000000  0000000000000000  00000198  2**0
                  CONTENTS
SYMBOL TABLE:
0000000000001000 g       03 ABS    01 0010 __mh_execute_header
0000000000001fff g       0f SECT   01 0000 [.text] _start

Disassembly of section .text:

0000000000001fff <_start>:
    1fff:       c3                      retq

关于linux - 我可以在MacOS的_start处通过代码执行 `ret`指令吗？ Linux的？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/47801580/