LibC+Kernel: Remove global variable use from snprintf and fprintf

The global variable use in these functions is super thread-unsafe and
means that any concurrent calls to sprintf or fprintf in a process
could race with each other and end up writing unexpected results.
We can just replace the function + global variable with a lambda that
captures the relevant argument when calling printf_internal instead.

Kernel/kprintf.cpp

@@ -123,26 +123,24 @@ int sprintf(char* buffer, const char* fmt, ...)
  return ret;
 }
 
-static size_t __vsnprintf_space_remaining;
-ALWAYS_INLINE void sized_buffer_putch(char*& bufptr, char ch)
-{
- if (__vsnprintf_space_remaining) {
- *bufptr++ = ch;
- --__vsnprintf_space_remaining;
- }
-}
-
 int snprintf(char* buffer, size_t size, const char* fmt, ...)
 {
  va_list ap;
  va_start(ap, fmt);
+ size_t space_remaining = 0;
  if (size) {
- __vsnprintf_space_remaining = size - 1;
+ space_remaining = size - 1;
  } else {
- __vsnprintf_space_remaining = 0;
+ space_remaining = 0;
  }
+ auto sized_buffer_putch = [&](char*& bufptr, char ch) {
+ if (space_remaining) {
+ *bufptr++ = ch;
+ --space_remaining;
+ }
+ };
  int ret = printf_internal(sized_buffer_putch, buffer, fmt, ap);
- if (__vsnprintf_space_remaining) {
+ if (space_remaining) {
  buffer[ret] = '\0';
  } else if (size > 0) {
  buffer[size - 1] = '\0';

Userland/Libraries/LibC/stdio.cpp

@@ -870,17 +870,10 @@ ALWAYS_INLINE void stdout_putch(char*&, char ch)
  putchar(ch);
 }
 
-static FILE* __current_stream = nullptr;
-ALWAYS_INLINE static void stream_putch(char*&, char ch)
-{
- fputc(ch, __current_stream);
-}
-
 // https://pubs.opengroup.org/onlinepubs/9699919799/functions/vfprintf.html
 int vfprintf(FILE* stream, const char* fmt, va_list ap)
 {
- __current_stream = stream;
- return printf_internal(stream_putch, nullptr, fmt, ap);
+ return printf_internal([stream](auto, char ch) { fputc(ch, stream); }, nullptr, fmt, ap);
 }
 
 // https://pubs.opengroup.org/onlinepubs/9699919799/functions/fprintf.html
@@ -957,25 +950,23 @@ int sprintf(char* buffer, const char* fmt, ...)
  return ret;
 }
 
-static size_t __vsnprintf_space_remaining;
-ALWAYS_INLINE void sized_buffer_putch(char*& bufptr, char ch)
-{
- if (__vsnprintf_space_remaining) {
- *bufptr++ = ch;
- --__vsnprintf_space_remaining;
- }
-}
-
 // https://pubs.opengroup.org/onlinepubs/9699919799/functions/vsnprintf.html
 int vsnprintf(char* buffer, size_t size, const char* fmt, va_list ap)
 {
+ size_t space_remaining = 0;
  if (size) {
- __vsnprintf_space_remaining = size - 1;
+ space_remaining = size - 1;
  } else {
- __vsnprintf_space_remaining = 0;
+ space_remaining = 0;
  }
+ auto sized_buffer_putch = [&](char*& bufptr, char ch) {
+ if (space_remaining) {
+ *bufptr++ = ch;
+ --space_remaining;
+ }
+ };
  int ret = printf_internal(sized_buffer_putch, buffer, fmt, ap);
- if (__vsnprintf_space_remaining) {
+ if (space_remaining) {
  buffer[ret] = '\0';
  } else if (size > 0) {
  buffer[size - 1] = '\0';