我正在嘗試用 C 構建一個自定義內核，我想在螢屏上放置一個彩色像素。
我已經切換到保護模式并將VGA模式設定為0x13，所以我用C撰寫了一個函式，在螢屏的右上角放置一個粉紅色像素：
#include <stdint.h>
#define VGA_MODE 0x13
#define VRAM 0xA0000
#define MAX_HEIGHT 200
#define MAX_LENGTH 320
void PutPixel(uint8_t color, uint16_t x)
{
// Return if x greater than 320
if(x > MAX_LENGTH) return;
unsigned char* ptr = (unsigned char*) VRAM;
ptr = x;
*ptr = color;
return;
}
void KERNEL_MAIN()
{
PutPixel(5, 320);
return;
}
這段代碼運行得非常好，直到我想將一個 y 偏移量作為引數添加到我的 PutPixel 函式中，以便在另一行上繪制一個像素：
#include <stdint.h>
#define VGA_MODE 0x13
#define VRAM 0xA0000
#define MAX_HEIGHT 200
#define MAX_LENGTH 320
void PutPixel(uint8_t color, uint16_t x, uint16_t y)
{
// Return if x greater than 320
if(x > MAX_LENGTH) return;
unsigned char* ptr = (unsigned char*) VRAM;
ptr = x;
*ptr = color;
return;
}
void KERNEL_MAIN()
{
PutPixel(5, 320, 1);
return;
}
即使我實際上沒有使用該引數，當我在 VirtualBox 中運行代碼時，它也會立即崩潰，并且在 VirtualBox 除錯器中出現以下錯誤：
dbgf event: DBGFSTOP (hyper)
File: VINF_EM_TRIPLE_FAULT
Line: 0
Function: <NULL>
eax=000a013e ebx=00007eae ecx=00000005 edx=00000005 esi=00000000 edi=0000fff0
eip=00000083 esp=0002ffac ebp=490002ff iopl=0 nv up di pl nz na pe nc
cs=0008 ds=0010 es=0010 fs=0010 gs=0010 ss=0010 eflags=00200002
0008:00000083 f0 53 Illegal opcode
VBoxDbg>
我可以得到一些幫助嗎？
編輯：我發現堆疊被一個位元組弄亂了，所以我反匯編了函式呼叫，它看起來像這樣：
%0000000000007ee7 55 push ebp
%0000000000007ee8 48 dec eax
%0000000000007ee9 89 e5 mov ebp, esp
%0000000000007eeb 48 dec eax
%0000000000007eec 83 ec 10 sub esp, byte 000000010h
%0000000000007eef 89 d0 mov eax, edx
%0000000000007ef1 44 inc esp ;???
%0000000000007ef2 89 c2 mov edx, eax
%0000000000007ef4 88 4d 10 mov byte [ebp 010h], cl
%0000000000007ef7 66 89 45 18 mov word [ebp 018h], ax
%0000000000007efb 89 d0 mov eax, edx
%0000000000007efd 66 89 45 20 mov word [ebp 020h], ax
%0000000000007f01 66 81 7d 18 40 01 cmp word [ebp 018h], word 00140h
%0000000000007f07 77 1c jnbe 01ch (000007f25h)
%0000000000007f09 48 dec eax
%0000000000007f0a c7 45 f8 00 00 0a 00 mov dword [ebp-008h], 0000a0000h
%0000000000007f11 0f b7 45 18 movzx eax, [ebp 018h]
%0000000000007f15 48 dec eax
%0000000000007f16 01 45 f8 add dword [ebp-008h], eax
%0000000000007f19 48 dec eax
%0000000000007f1a 8b 45 f8 mov eax, dword [ebp-008h]
%0000000000007f1d 0f b6 55 10 movzx edx, byte [ebp 010h]
%0000000000007f21 88 10 mov byte [eax], dl
%0000000000007f23 eb 01 jmp 001h (000007f26h)
%0000000000007f25 90 nop
%0000000000007f26 48 dec eax
%0000000000007f27 83 c4 10 add esp, byte 000000010h
%0000000000007f2a 5d pop ebp
%0000000000007f2b c3 retn
When I discard the inc esp instruction at 0x7ef1,retn pops the return address correctly, but why is this instruction even there in the first place?
uj5u.com熱心網友回復：
我在添加編譯器選項時找到了解決方案：
gcc -mno-red-zone
它現在完美無缺，謝謝！
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標籤：c assembly x86 virtualbox
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