Error: variable-sized object may not be initialized?

Question

我正在为我的 OSDev OS 制作键盘驱动程序，我的 kbd.c:

有问题

kbd.c: In function 'scancoderec':
kbd.c:56:2: error: variable-sized object may not be initialized
register int (ScanCode[strlen(ValEAX)-8]) = 0x00; /* Remove last 8 bits from the value we gathered from EAX to get AH and make that the scancode. */

这是包含失败代码行的函数：

int scancoderec() {
  __asm__ volatile( "movl [=11=], %eax" ); /* Moving 00 to EAX. */
  __asm__ volatile( "int [=11=]x16 "); /*int 0x16 */
  register int ValEAX asm("eax"); /* Let's get eax */
  register int (ScanCode[strlen(ValEAX)-8]) = 0x00; /* Remove last 8 bits from the value we gathered from EAX to get AH and make that the scancode. */
}

为什么会这样？

编辑：我仍然认为 "ax" 未定义，这次是在另一个函数中。

kbd.c:65:27: error: 'ax' undeclared (first use in this function)
register int Key = kbdus[ax];

scancode函数和getkey函数代码：

    unsigned short scancodeget()
    {
       unsigned char ax = 0;    /* int 0x16, AH=0 is get keystroke */
       __asm__ __volatile__ ("int [=13=]x16\n\t"
                             : "+a"(ax)); 
       ax = ax >> 8;       /* Shift top 8 bits of ax to lower 8 bits */
                       /* ax now is the scancode returned by BIOS */
       return (unsigned short)ax; /* Return the lower 8 bits */
}

int getkey() { /*This could be used as a keyboard driver. */
       scancoderec(); /*Get our scancode! */
       int Key = kbdus[ax]; /*Use our kbdus array which i copied from a website since i seriously don't want to make an gigantic array */
}

Answer 1

错误信息已经很清楚了。您不能初始化可变长度数组。改写

register int (ScanCode[strlen(ValEAX)-8]);
ScanCode[0] = 0x00;

或者您可以使用标准 C 函数 memset，在 header <string.h> 中声明，将向量的所有元素设置为 0x00。

例如

memset( ScanCode, 0x00, sizeof( ScanCode ) );

Answer 2

行

register int (ScanCode[strlen(ValEAX)-8]) = 0x00;

声明一个 VLA 并尝试初始化它，这是不允许的。将其更改为：

// Declare
int size = strlen(ValEAX)-8
register int ScanCode[size];

// Set values.
for ( int i = 0; i < size; ++i )
{
   ScanCode[i] = 0x00;
}

Answer 3

很难说出您想要达到的目标。此例程 returns 从 BIOS interrupt 16h/AH=0h. It uses GCC extended assembler template using an input/output constraint 返回的原始扫描码将值为 0 的 AX 传递到汇编程序模板并检索 AX[ 中的值=31=] 之后。扫描码位于 ax 变量的高 8 位，因此我们将其右移 8 位。

#include <stdint.h> uint8_t getchar_scancode() { uint16_t ax = 0; /* int 0x16, AH=0 is get keystroke */ __asm__ __volatile__ ("int [=10=]x16\n\t" : "+a"(ax)); /* +a is an input and output constraint using EAX register */ /* The contents of the 'ax' variable will be transferred */ /* into EAX register upon entry, and the value of EAX register */ /* will be transferred into variable 'ax' when finished */ ax = ax >> 8; /* Shift top 8 bits of ax to lower 8 bits */ /* ax now is the scancode returned by BIOS */ return (uint8_t)ax; /* Return the lower 8 bits */ }

如果您没有stdint.h可用于定义uint16_t，您可以将其替换为unsigned short并将uint8_t替换为unsigned char。

如果您需要将扫描码转换为 ASCII 字符，您可以使用其他函数来提供该功能：

unsigned char kbdus[128] = { 0, 27, '1', '2', '3', '4', '5', '6', '7', '8', /* 9 */ '9', '0', '-', '=', '\b', /* Backspace */ '\t', /* Tab */ 'q', 'w', 'e', 'r', /* 19 */ 't', 'y', 'u', 'i', 'o', 'p', '[', ']', '\n', /* Enter key */ 0, /* 29 - Control */ 'a', 's', 'd', 'f', 'g', 'h', 'j', 'k', 'l', ';', /* 39 */ '\'', '`', 0, /* Left shift */ '\', 'z', 'x', 'c', 'v', 'b', 'n', /* 49 */ 'm', ',', '.', '/', 0, /* Right shift */ '*', 0, /* Alt */ ' ', /* Space bar */ 0, /* Caps lock */ 0, /* 59 - F1 key ... > */ 0, 0, 0, 0, 0, 0, 0, 0, 0, /* < ... F10 */ 0, /* 69 - Num lock*/ 0, /* Scroll Lock */ 0, /* Home key */ 0, /* Up Arrow */ 0, /* Page Up */ '-', 0, /* Left Arrow */ 0, 0, /* Right Arrow */ '+', 0, /* 79 - End key*/ 0, /* Down Arrow */ 0, /* Page Down */ 0, /* Insert Key */ 0, /* Delete Key */ 0, 0, 0, 0, /* F11 Key */ 0, /* F12 Key */ 0, /* All other keys are undefined */ }; uint8_t getchar() { return (kbdus[getchar_scancode()]); }

BIOS 中断不会在保护模式下工作，并且可能会导致机器出现故障。 INT 16h/AH=0 仅在实模式下有效。

Error: variable-sized object may not be initialized?

Error: variable-sized object may not be initialized?

gcc

x86

keyboard-events

inline-assembly

osdev