32/64位asm

1、Interfacing HLL code with asm

1.1、C calling convention – standard stack frame

Arguments passed to a C function are pushed onto the stack, right to left, before the function is called. The first thing the called function does is push the (E)BP register, then copy (E)SP into it. This creates a data structure called the standard C stack frame.

 32-bit code16-bit code, TINY, SMALL, or COMPACT memory models16-bit code, MEDIUM, LARGE, or HUGE memory modelsCreate standard stack frame, allocate 16 bytes for local variables, save registerspush ebp

mov ebp,esp

sub esp,16

push edi

push esi

…

push bp

mov bp,sp

sub sp,16

push di

push si

…

push bp

mov bp,sp

sub sp,16

push di

push si

…

Restore registers, destroy stack frame, and return…

pop esi

pop edi

mov esp,ebp

pop ebp

ret

…

pop si

pop di

mov sp,bp

pop bp

ret

…

pop si

pop di

mov sp,bp

pop bp

retf

Size of ‘slots’ in stack frame, i.e. stack width32 bits16 bits16 bitsLocation of stack frame ‘slots’[ebp + 8]
[ebp + 12]
[ebp + 16]…[bp + 4]
[bp + 6]
[bp + 8]…[bp + 6]
[bp + 8]
[bp + 10]…

If an argument passed to a function is wider than the stack, it will occupy more than one ‘slot’ in the stack frame. A 64-bit value passed to a function (long long or double) will occupy 2 stack slots in 32-bit code or 4 stack slots in 16-bit code.

Function arguments are accessed with positive offsets from the BP or EBP registers. Local variables are accessed with negative offsets. The previous value of BP or EBP is stored at [bp + 0] or [ebp + 0]. The return address (IP or EIP) is stored at [bp + 2] or [ebp + 4].

１.２、C calling convention – return values

A C function usually stores its return value in one or more registers.

 32-bit code16-bit code, all memory models8-bit return valueALAL16-bit return valueAXAX32-bit return valueEAXDX:AX64-bit return valueEDX:EAXspace for the return value is allocated on the stack of the calling function, and a ‘hidden’ pointer to this space is passed to the called function128-bit return valuehidden pointerhidden pointer

１.３、C calling convention – saving registers

GCC expects functions to preserve the callee-save registers:

EBX, EDI, ESI, EBP, DS, ES, SS

You need not save these registers:

EAX, ECX, EDX, FS, GS, EFLAGS, floating point registers

In some OSes, FS or GS may be used as a pointer to thread local storage (TLS), and must be saved if you modify it.

１.４、C calling convention – leading underscores

Some C compilers (those for DOS and Windows, and those with COFF output) prepend an underscore to the names of C functions and global variables. If a C global variable, e.g. conv_mem_size, is accessed by asm code, it should be declared with a leading underscore in the asm code:

EXTERN _conv_mem_size      ; NASM syntax

mov [_conv_mem_size],ax

Linux ELF does NOT use underscores. Watcom C uses trailing underscores for function names, and leading underscores for global variables.

If your GCC supports it, leading underscores can be turned off with the compiler option -fno-leading-underscore

Pascal calling conventions

Function arguments are pushed onto the stack from left to right before the function is called. C-style variable-length argument lists are not possible in Pascal. (Look in file STDARG.H and think about it.)

In C, the calling function must ‘clean up the stack’ (remove function arguments from the stack after the called function returns). In Pascal, the called function must do this, before returning.

Pascal identifiers are case-insensitive. MyKewlProc() will be stored in the object code file as MYKEWLPROC

Other calling conventions

The __stdcall calling convention, used by Windows, is a hybrid of the C and Pascal calling conventions. Like C, function arguments are pushed right-to-left. Like Pascal, the called function must clean up the stack. Exception: the caller must clean up the stack for functions that accept a variable number of arguments, e.g. printf(const char *format, …);

Watcom C uses a register-based calling convention. See sections 7.4, 7.5, 10.4, and 10.5 in cuserguide.pdf in the Watcom documentation. Individual functions can be declared to use the normal, stack-based calling convention.

GCC can be made to use a register calling convention by compiling with gcc -mregparm=NNN …
See the GCC documentation for details.

参考网址：http://www.hoverlees.com/blog/?p=17

参考网址：https://eli.thegreenplace.net/2011/09/06/stack-frame-layout-on-x86-64

参考网址：http://www.cs.virginia.edu/~evans/cs216/guides/x86.html