asm 32/64区别

1、系统调用及C函数调用，参数传递方式不同

• User-level applications use as integer registers for passing the sequence %rdi, %rsi, %rdx, %rcx, %r8 and %r9. The kernel interface uses %rdi, %rsi, %rdx, %r10, %r8 and %r9.
• A system-call is done via the syscall instruction. The kernel destroys registers %rcx and %r11.
• The number of the syscall has to be passed in register %rax.
• System-calls are limited to six arguments, no argument is passed directly on the stack.
• Returning from the syscall, register %rax contains the result of the system-call. A value in the range between -4095 and -1 indicates an error, it is -errno.
• Only values of class INTEGER or class MEMORY are passed to the kernel.

2、调用指令不同

• For a 32bit kernel, SYSENTER/SYSEXIT are the only compatible pair [between AMD and Intel CPUs]
• For a 64bit kernel in Long mode only… SYSCALL/SYSRET are the only compatible pair [between AMD and Intel CPUs]

3、syscall的call number不同

• 32bit 定义在unistd_32.h
• 64bit 定义在unistd_64.h