我正在使用 C 設計我的內核。在制作kprintf函式（類似printf但與內核一起使用的函式）時，我看到有符號整數（準確地說資料型別是long），va_args正在將它們轉換為unsigned long.
這是代碼片段：
kPrint.c
#include <stdarg.h>
// skipped some lines not needed for this question
// ...
/******************
* global variables needed for number to string conversion
* ***************/
// store the converted string temporarily
static char convertedString[30];
// store the index of the filled portion
static char numberIndex;
// TODO: Create function like printf but which works here
_Bool kprintf(const char* stringFormat, ...) {
char* strPtr = (char*)stringFormat;
va_list arguements;
va_start(arguements, stringFormat);
while (*strPtr != 0) {
switch (*strPtr)
{
case '\e':
// printf() also ends the execution
return 1;
case '%':
switch (*(strPtr 1))
{
// signed decimal integer
case 'd':
case 'i':
kprintf(IntToString(va_arg(arguements, long long))); // stringify the integer
// *problem* here
strPtr = 2;
break;
// unsigned decimal integer
case 'u':
kprintf(uIntToString(va_arg(arguements, uint64_t))); // stringify
strPtr = 2;
break;
// will implement U & L case later
// unsigned hexadecimal
case 'x':
case 'X':
kprintf(uHexToString(va_arg(arguements, uint64_t))); // stringify
// doesn't work now
strPtr = 2;
break;
// will implement U & L case later
// 6 numbers after decimal
case 'f':
case 'F':
kprintf(DoubleToString(va_arg(arguements, double), 6)); // stringify
// doesn't work now
strPtr = 2;
break;
// 2 numbers after pt
case 'g':
case 'G':
kprintf(DoubleToString(va_arg(arguements, double), 2));
strPtr = 2;
break;
case 'c':
kPrintChar((char)va_arg(arguements, int));
//
strPtr = 2;
break;
// another string
case 's':
kPrintfHelper(va_arg(arguements, char*)); // just to prevent recursion
strPtr = 2;
break;
case '%':
kPrintChar('%');
strPtr = 2;
break;
}
break;
default:
kPrintChar(*strPtr);
strPtr ;
}
}
va_end(arguements);
return 0;
}
void uIntToStrHelper(uint64_t num) {
if (num < 10)
{
convertedString[numberIndex ] = num '0';
convertedString[numberIndex] = 0;
return;
}
uint8_t numIndexCpy = numberIndex;
while (num > 0) {
convertedString[numberIndex ] = (num % 10) '0';
num /= 10;
}
char swpIndex = (numberIndex - 2 numIndexCpy) / 2;
numberIndex = numberIndex - swpIndex - 1 numIndexCpy;
while (swpIndex >= numIndexCpy) {
convertedString[swpIndex] = convertedString[swpIndex]
convertedString[numberIndex];
convertedString[numberIndex] = convertedString[swpIndex] -
convertedString[numberIndex];
convertedString[swpIndex] = convertedString[swpIndex] -
convertedString[numberIndex];
swpIndex--;
numberIndex ;
}
convertedString[numberIndex] = 0;
}
char* uIntToString(uint64_t num) {
numberIndex = 0;
uIntToStrHelper(num);
return convertedString;
}
char* IntToString(long long num) {
numberIndex = 0;
if (num < 0) {
convertedString[numberIndex ] = '-';
num = -num;
}
uIntToStrHelper(num);
return convertedString;
}
編輯：添加IntToString和uIntToString.
（我不知道這樣做的正確方法，但它就足夠了）
問題概述：
“d”和“i”的案例顯示了問題所在。
的函式原型IntToString：
char* IntToString(long long num);
// part of the reason why I used long long as va_arg data type
// had also tried with long but with no luck :(
我已經在 linux 機器上嘗試過IntToString&功能，它們按預期的方式作業。uIntToString
注意：我沒有kprintf(const char* stringFormat, ...)像上面提到的其他 2 個函式那樣在受控且易于除錯的環境中進行測驗。
Other functions like DoubleToString and uHexToString have not yet been tested but it should not change/be related to the question anyway.
kPrintfHelper is a function just like kprintf but does not do any checking and just prints the string
My Environment
Compiler: x86_64-elf-gcc
Flags (aka CFLAGS): -ffreestanding -mno-red-zone -m64
Linker: x86_64-elf-ld
I use qemu-system-x86_64 to run the final executable.
Tests
I have tried the following cases:
- Normal unsigned case
kprintf("Number: %d\n", 1234);
Output:
Number: 1234
- Does not work but the output seems like
va_argsis doing some weird unsignedintmath (further proved by test 5 that it was indeedva_args, IMO)
kprintf("Number: %d\n", -1234);
Output:
Number: 4294966062
- Works as intended
kprintf("Number: %d\n", 1099511627775);
Output:
Number: 1099511627775
- BUT This
kprintf("Number: %d\n", -1099511627775);
Output:
Number: 1099511627775
- AND here
kprintf("Number: %s\n", IntToString(-1234));
Output:
Number: -1234
uj5u.com熱心網友回復：
您為說明符傳遞的值的型別與預期的%d不匹配。va_arg
你告訴va_arg期望 a long long，但是1234并且-1234有 type int。這些型別的大小不同，因此va_arg從呼叫堆疊中提取的位元組數比您放入的位元組數多。
標準格式說明符具有大小修飾符，因此它們可以處理不同的大小型別。你需要實作類似的東西。
uj5u.com熱心網友回復：
呼叫kprintf("Number: %d\n", -1234);不正確，因為%d提取了long long. 一定是kprintf("Number: %d\n", -1234LL);。
-1234 是 32 位運算元。問題可能是這是在一個 64 位對齊的字中傳遞的，但沒有被符號擴展到 64 位。
也就是說，64位中的-1234值需要是fffffffffffffb2e，但是32位引數00000000fffffb2e在堆疊上產生了一個影像，即4294966062。
然而，根據這個假設，我們必須通過 -1000 才能獲得觀察到的 429496629。它與 -1234 無關。可能會發生其他事情，例如垃圾位被解釋為資料。
畢竟，這種行為并沒有明確定義：您將一個大小的整數推入一個完全無型別且不安全的引數傳遞機制并取出一個不同大小的整數。
轉載請註明出處，本文鏈接：https://www.uj5u.com/yidong/455729.html
標籤：c string variadic-functions elf unsigned-integer
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