在 DOS 上使用 C 汇编例程
我已经使用 DOS 实模式汇编有一段时间了，现在我想在 C 程序中利用一些例程。我正在使用 Turbo C 2.01 和 TASM 3.0。但是，我无法修改通过地址传递的变量，请参阅下面的 _setval 例程。我不需要/想要内联汇编。一个简单的例子：
foo.c
#include <stdio.h>
extern void setval(int *x, int *y);
extern int sum(int x, int y);
int main()
{
int result, a, b;
result = a = b = 0;
setval(&a, &b);
result = a + b;
printf("a+b=%i, a=%i, b=%i\n", result, a, b);
result = 0;
a = 42;
b = 19;
result = sum(a, b);
printf("a+b=%i, a=%i, b=%i\n", result, a, b);
return 0;
}
foortn.asm
public _setval
public _sum
.model small
.stack
.data
.code
_setval proc near
push bp
mov bp, sp
mov word ptr [bp+4], 42
mov word ptr [bp+6], 19
pop bp
ret
endp
_sum proc near
push bp
mov bp, sp
mov ax, word ptr [bp+4]
add ax, word ptr [bp+6]
pop bp
ret
endp
end
我像这样编译它：
tcc -c -ms foo.c
tasm /ml foortn.asm
tcc foo.obj foortn.obj
结果是：
a+b=0, a=0, b=0
a+b=61, a=42, b=19
我显然错过了一些东西，但是什么呢？
汉斯、马克和比尔，非常感谢你们及时而有用的回复。
I've been playing with DOS real mode assembly for a while and now I want to utilize some routines in a C program. I'm using Turbo C 2.01 and TASM 3.0. I'm however unable to modify a variable passed by address, see the _setval routine below. I don't need/want inline assembly. A simple example:
foo.c
#include <stdio.h>
extern void setval(int *x, int *y);
extern int sum(int x, int y);
int main()
{
int result, a, b;
result = a = b = 0;
setval(&a, &b);
result = a + b;
printf("a+b=%i, a=%i, b=%i\n", result, a, b);
result = 0;
a = 42;
b = 19;
result = sum(a, b);
printf("a+b=%i, a=%i, b=%i\n", result, a, b);
return 0;
}
foortn.asm
public _setval
public _sum
.model small
.stack
.data
.code
_setval proc near
push bp
mov bp, sp
mov word ptr [bp+4], 42
mov word ptr [bp+6], 19
pop bp
ret
endp
_sum proc near
push bp
mov bp, sp
mov ax, word ptr [bp+4]
add ax, word ptr [bp+6]
pop bp
ret
endp
end
I compile it like this:
tcc -c -ms foo.c
tasm /ml foortn.asm
tcc foo.obj foortn.obj
The result is:
a+b=0, a=0, b=0
a+b=61, a=42, b=19
I'm obviously missing something, but what?
Hans, Mark and Bill, thank you very much for your prompt and helpful responses.
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评论（4）
您当前的代码正在覆盖传递的指针。您需要检索指针并写入它。像这样的事情：
首先用 C 编写此代码，然后查看它生成的汇编代码以确保正确。
Your current code is overwriting the passed pointer. You need to retrieve the pointer and write through it. Something like this:
Write this code in C first and look at the assembly code that it generates to get this right.
尝试替换：
与
Try replacing:
with
这是：
正在写入堆栈，而不是堆栈上的地址。您需要读取堆栈上的地址，然后写入它们：
This:
is writing to the stack, not the addresses on the stack. You'll need to read the addresses on the stack, then write to them instead:
我不知道汇编程序...但是
C按值传递所有内容。在
sum中，[bp+4] 是 42（或 19）；在addsetval[bp+4] 中是0xDEADBEEF0xDECAFBAD （或其他）I don't know assembler ... but
Cpasses everything by value.In
sum[bp+4] is 42 (or 19); inaddsetval[bp+4] is0xDEADBEEF0xDECAFBAD (or whatever)