lib/sanitizer_common/sanitizer_printf.cpp - llvm-project/compiler-rt - Git at Google

 //===-- sanitizer_printf.cpp ----------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
 // This file is shared between AddressSanitizer and ThreadSanitizer.
 //
 // Internal printf function, used inside run-time libraries.
 // We can't use libc printf because we intercept some of the functions used
 // inside it.
 //===----------------------------------------------------------------------===//

 #include "sanitizer_common.h"
 #include "sanitizer_flags.h"
 #include "sanitizer_libc.h"

 #include <stdio.h>
 #include <stdarg.h>

 #if SANITIZER_WINDOWS && defined(_MSC_VER) && _MSC_VER < 1800 &&               \
       !defined(va_copy)
 # define va_copy(dst, src) ((dst) = (src))
 #endif

 namespace __sanitizer {

 static int AppendChar(char **buff, const char *buff_end, char c) {
   if (*buff < buff_end) {
     **buff = c;
     (*buff)++;
   }
   return 1;
 }

 // Appends number in a given base to buffer. If its length is less than
 // |minimal_num_length|, it is padded with leading zeroes or spaces, depending
 // on the value of |pad_with_zero|.
 static int AppendNumber(char **buff, const char *buff_end, u64 absolute_value,
                         u8 base, u8 minimal_num_length, bool pad_with_zero,
                         bool negative, bool uppercase) {
   uptr const kMaxLen = 30;
   RAW_CHECK(base == 10 || base == 16);
   RAW_CHECK(base == 10 || !negative);
   RAW_CHECK(absolute_value || !negative);
   RAW_CHECK(minimal_num_length < kMaxLen);
   int result = 0;
   if (negative && minimal_num_length)
     --minimal_num_length;
   if (negative && pad_with_zero)
     result += AppendChar(buff, buff_end, '-');
   uptr num_buffer[kMaxLen];
   int pos = 0;
   do {
     RAW_CHECK_MSG((uptr)pos < kMaxLen, "AppendNumber buffer overflow");
     num_buffer[pos++] = absolute_value % base;
     absolute_value /= base;
   } while (absolute_value > 0);
   if (pos < minimal_num_length) {
     // Make sure compiler doesn't insert call to memset here.
     internal_memset(&num_buffer[pos], 0,
                     sizeof(num_buffer[0]) * (minimal_num_length - pos));
     pos = minimal_num_length;
   }
   RAW_CHECK(pos > 0);
   pos--;
   for (; pos >= 0 && num_buffer[pos] == 0; pos--) {
     char c = (pad_with_zero || pos == 0) ? '0' : ' ';
     result += AppendChar(buff, buff_end, c);
   }
   if (negative && !pad_with_zero) result += AppendChar(buff, buff_end, '-');
   for (; pos >= 0; pos--) {
     char digit = static_cast<char>(num_buffer[pos]);
     digit = (digit < 10) ? '0' + digit : (uppercase ? 'A' : 'a') + digit - 10;
     result += AppendChar(buff, buff_end, digit);
   }
   return result;
 }

 static int AppendUnsigned(char **buff, const char *buff_end, u64 num, u8 base,
                           u8 minimal_num_length, bool pad_with_zero,
                           bool uppercase) {
   return AppendNumber(buff, buff_end, num, base, minimal_num_length,
                       pad_with_zero, false /* negative */, uppercase);
 }

 static int AppendSignedDecimal(char **buff, const char *buff_end, s64 num,
                                u8 minimal_num_length, bool pad_with_zero) {
   bool negative = (num < 0);
   return AppendNumber(buff, buff_end, (u64)(negative ? -num : num), 10,
                       minimal_num_length, pad_with_zero, negative,
                       false /* uppercase */);
 }


 // Use the fact that explicitly requesting 0 width (%0s) results in UB and
 // interpret width == 0 as "no width requested":
 // width == 0 - no width requested
 // width  < 0 - left-justify s within and pad it to -width chars, if necessary
 // width  > 0 - right-justify s, not implemented yet
 static int AppendString(char **buff, const char *buff_end, int width,
                         int max_chars, const char *s) {
   if (!s)
     s = "<null>";
   int result = 0;
   for (; *s; s++) {
     if (max_chars >= 0 && result >= max_chars)
       break;
     result += AppendChar(buff, buff_end, *s);
   }
   // Only the left justified strings are supported.
   while (width < -result)
     result += AppendChar(buff, buff_end, ' ');
   return result;
 }

 static int AppendPointer(char **buff, const char *buff_end, u64 ptr_value) {
   int result = 0;
   result += AppendString(buff, buff_end, 0, -1, "0x");
   result += AppendUnsigned(buff, buff_end, ptr_value, 16,
                            SANITIZER_POINTER_FORMAT_LENGTH,
                            true /* pad_with_zero */, false /* uppercase */);
   return result;
 }

 int VSNPrintf(char *buff, int buff_length,
               const char *format, va_list args) {
   static const char *kPrintfFormatsHelp =
       "Supported Printf formats: %([0-9]*)?(z|l|ll)?{d,u,x,X}; %p; "
       "%[-]([0-9]*)?(\\.\\*)?s; %c\nProvided format: ";
   RAW_CHECK(format);
   RAW_CHECK(buff_length > 0);
   const char *buff_end = &buff[buff_length - 1];
   const char *cur = format;
   int result = 0;
   for (; *cur; cur++) {
     if (*cur != '%') {
       result += AppendChar(&buff, buff_end, *cur);
       continue;
     }
     cur++;
     bool left_justified = *cur == '-';
     if (left_justified)
       cur++;
     bool have_width = (*cur >= '0' && *cur <= '9');
     bool pad_with_zero = (*cur == '0');
     int width = 0;
     if (have_width) {
       while (*cur >= '0' && *cur <= '9') {
         width = width * 10 + *cur++ - '0';
       }
     }
     bool have_precision = (cur[0] == '.' && cur[1] == '*');
     int precision = -1;
     if (have_precision) {
       cur += 2;
       precision = va_arg(args, int);
     }
     bool have_z = (*cur == 'z');
     cur += have_z;
     bool have_l = cur[0] == 'l' && cur[1] != 'l';
     cur += have_l;
     bool have_ll = cur[0] == 'l' && cur[1] == 'l';
     cur += have_ll * 2;
     const bool have_length = have_z || have_l || have_ll;
     const bool have_flags = have_width || have_length;
     // At the moment only %s supports precision and left-justification.
     CHECK(!((precision >= 0 || left_justified) && *cur != 's'));
     switch (*cur) {
       case 'd': {
         s64 dval = have_ll  ? va_arg(args, s64)
                    : have_z ? va_arg(args, sptr)
                    : have_l ? va_arg(args, long)
                             : va_arg(args, int);
         result += AppendSignedDecimal(&buff, buff_end, dval, width,
                                       pad_with_zero);
         break;
       }
       case 'u':
       case 'x':
       case 'X': {
         u64 uval = have_ll  ? va_arg(args, u64)
                    : have_z ? va_arg(args, uptr)
                    : have_l ? va_arg(args, unsigned long)
                             : va_arg(args, unsigned);
         bool uppercase = (*cur == 'X');
         result += AppendUnsigned(&buff, buff_end, uval, (*cur == 'u') ? 10 : 16,
                                  width, pad_with_zero, uppercase);
         break;
       }
       case 'p': {
         RAW_CHECK_VA(!have_flags, kPrintfFormatsHelp, format);
         result += AppendPointer(&buff, buff_end, va_arg(args, uptr));
         break;
       }
       case 's': {
         RAW_CHECK_VA(!have_length, kPrintfFormatsHelp, format);
         // Only left-justified width is supported.
         CHECK(!have_width || left_justified);
         result += AppendString(&buff, buff_end, left_justified ? -width : width,
                                precision, va_arg(args, char*));
         break;
       }
       case 'c': {
         RAW_CHECK_VA(!have_flags, kPrintfFormatsHelp, format);
         result += AppendChar(&buff, buff_end, va_arg(args, int));
         break;
       }
       case '%' : {
         RAW_CHECK_VA(!have_flags, kPrintfFormatsHelp, format);
         result += AppendChar(&buff, buff_end, '%');
         break;
       }
       default: {
         RAW_CHECK_VA(false, kPrintfFormatsHelp, format);
       }
     }
   }
   RAW_CHECK(buff <= buff_end);
   AppendChar(&buff, buff_end + 1, '\0');
   return result;
 }

 static void (*PrintfAndReportCallback)(const char *);
 void SetPrintfAndReportCallback(void (*callback)(const char *)) {
   PrintfAndReportCallback = callback;
 }

 // Can be overriden in frontend.
 #if SANITIZER_GO && defined(TSAN_EXTERNAL_HOOKS)
 // Implementation must be defined in frontend.
 extern "C" void __sanitizer_on_print(const char *str);
 #else
 SANITIZER_INTERFACE_WEAK_DEF(void, __sanitizer_on_print, const char *str) {
   (void)str;
 }
 #endif

 static void CallPrintfAndReportCallback(const char *str) {
   __sanitizer_on_print(str);
   if (PrintfAndReportCallback)
     PrintfAndReportCallback(str);
 }

 static void NOINLINE SharedPrintfCodeNoBuffer(bool append_pid,
                                               char *local_buffer,
                                               int buffer_size,
                                               const char *format,
                                               va_list args) {
   va_list args2;
   va_copy(args2, args);
   InternalMmapVector<char> v;
   int needed_length = 0;
   char *buffer = local_buffer;
   // First try to print a message using a local buffer, and then fall back to
   // mmaped buffer.
   for (int use_mmap = 0;; use_mmap++) {
     if (use_mmap) {
       va_end(args);
       va_copy(args, args2);
       v.resize(needed_length + 1);
       buffer_size = v.capacity();
       v.resize(buffer_size);
       buffer = &v[0];
     }
     needed_length = 0;
     // Fuchsia's logging infrastructure always keeps track of the logging
     // process, thread, and timestamp, so never prepend such information.
     if (!SANITIZER_FUCHSIA && append_pid) {
       int pid = internal_getpid();
       const char *exe_name = GetProcessName();
       if (common_flags()->log_exe_name && exe_name) {
         needed_length += internal_snprintf(buffer, buffer_size,
                                            "==%s", exe_name);
         if (needed_length >= buffer_size)
           continue;
       }
       needed_length += internal_snprintf(
           buffer + needed_length, buffer_size - needed_length, "==%d==", pid);
       if (needed_length >= buffer_size)
         continue;
     }
     needed_length += VSNPrintf(buffer + needed_length,
                                buffer_size - needed_length, format, args);
     if (needed_length >= buffer_size)
       continue;
     // If the message fit into the buffer, print it and exit.
     break;
   }
   RawWrite(buffer);

   // Remove color sequences from the message.
   RemoveANSIEscapeSequencesFromString(buffer);
   CallPrintfAndReportCallback(buffer);
   LogMessageOnPrintf(buffer);

   va_end(args2);
 }

 static void NOINLINE SharedPrintfCode(bool append_pid, const char *format,
                                       va_list args) {
   // |local_buffer| is small enough not to overflow the stack and/or violate
   // the stack limit enforced by TSan (-Wframe-larger-than=512). On the other
   // hand, the bigger the buffer is, the more the chance the error report will
   // fit into it.
   char local_buffer[400];
   SharedPrintfCodeNoBuffer(append_pid, local_buffer, ARRAY_SIZE(local_buffer),
                            format, args);
 }

 void Printf(const char *format, ...) {
   va_list args;
   va_start(args, format);
   SharedPrintfCode(false, format, args);
   va_end(args);
 }

 // Like Printf, but prints the current PID before the output string.
 void Report(const char *format, ...) {
   va_list args;
   va_start(args, format);
   SharedPrintfCode(true, format, args);
   va_end(args);
 }

 // Writes at most "length" symbols to "buffer" (including trailing '\0').
 // Returns the number of symbols that should have been written to buffer
 // (not including trailing '\0'). Thus, the string is truncated
 // iff return value is not less than "length".
 int internal_snprintf(char *buffer, uptr length, const char *format, ...) {
   va_list args;
   va_start(args, format);
   int needed_length = VSNPrintf(buffer, length, format, args);
   va_end(args);
   return needed_length;
 }

 void InternalScopedString::append(const char *format, ...) {
   uptr prev_len = length();

   while (true) {
     buffer_.resize(buffer_.capacity());

     va_list args;
     va_start(args, format);
     uptr sz = VSNPrintf(buffer_.data() + prev_len, buffer_.size() - prev_len,
                         format, args);
     va_end(args);
     if (sz < buffer_.size() - prev_len) {
       buffer_.resize(prev_len + sz + 1);
       break;
     }

     buffer_.reserve(buffer_.capacity() * 2);
   }
   CHECK_EQ(buffer_[length()], '\0');
 }

 } // namespace __sanitizer
	//===-- sanitizer_printf.cpp ----------------------------------------------===//
	//
	// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
	// See https://llvm.org/LICENSE.txt for license information.
	// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
	//
	//===----------------------------------------------------------------------===//
	//
	// This file is shared between AddressSanitizer and ThreadSanitizer.
	//
	// Internal printf function, used inside run-time libraries.
	// We can't use libc printf because we intercept some of the functions used
	// inside it.
	//===----------------------------------------------------------------------===//

	#include "sanitizer_common.h"
	#include "sanitizer_flags.h"
	#include "sanitizer_libc.h"

	#include <stdio.h>
	#include <stdarg.h>

	#if SANITIZER_WINDOWS && defined(_MSC_VER) && _MSC_VER < 1800 && \
	!defined(va_copy)
	# define va_copy(dst, src) ((dst) = (src))
	#endif

	namespace __sanitizer {

	static int AppendChar(char *buff, const char buff_end, char c) {
	if (*buff < buff_end) {
	**buff = c;
	(*buff)++;
	}
	return 1;
	}

	// Appends number in a given base to buffer. If its length is less than
	// \|minimal_num_length\|, it is padded with leading zeroes or spaces, depending
	// on the value of \|pad_with_zero\|.
	static int AppendNumber(char *buff, const char buff_end, u64 absolute_value,
	u8 base, u8 minimal_num_length, bool pad_with_zero,
	bool negative, bool uppercase) {
	uptr const kMaxLen = 30;
	RAW_CHECK(base == 10 \|\| base == 16);
	RAW_CHECK(base == 10 \|\| !negative);
	RAW_CHECK(absolute_value \|\| !negative);
	RAW_CHECK(minimal_num_length < kMaxLen);
	int result = 0;
	if (negative && minimal_num_length)
	--minimal_num_length;
	if (negative && pad_with_zero)
	result += AppendChar(buff, buff_end, '-');
	uptr num_buffer[kMaxLen];
	int pos = 0;
	do {
	RAW_CHECK_MSG((uptr)pos < kMaxLen, "AppendNumber buffer overflow");
	num_buffer[pos++] = absolute_value % base;
	absolute_value /= base;
	} while (absolute_value > 0);
	if (pos < minimal_num_length) {
	// Make sure compiler doesn't insert call to memset here.
	internal_memset(&num_buffer[pos], 0,
	sizeof(num_buffer[0]) * (minimal_num_length - pos));
	pos = minimal_num_length;
	}
	RAW_CHECK(pos > 0);
	pos--;
	for (; pos >= 0 && num_buffer[pos] == 0; pos--) {
	char c = (pad_with_zero \|\| pos == 0) ? '0' : ' ';
	result += AppendChar(buff, buff_end, c);
	}
	if (negative && !pad_with_zero) result += AppendChar(buff, buff_end, '-');
	for (; pos >= 0; pos--) {
	char digit = static_cast<char>(num_buffer[pos]);
	digit = (digit < 10) ? '0' + digit : (uppercase ? 'A' : 'a') + digit - 10;
	result += AppendChar(buff, buff_end, digit);
	}
	return result;
	}

	static int AppendUnsigned(char *buff, const char buff_end, u64 num, u8 base,
	u8 minimal_num_length, bool pad_with_zero,
	bool uppercase) {
	return AppendNumber(buff, buff_end, num, base, minimal_num_length,
	pad_with_zero, false /* negative */, uppercase);
	}

	static int AppendSignedDecimal(char *buff, const char buff_end, s64 num,
	u8 minimal_num_length, bool pad_with_zero) {
	bool negative = (num < 0);
	return AppendNumber(buff, buff_end, (u64)(negative ? -num : num), 10,
	minimal_num_length, pad_with_zero, negative,
	false /* uppercase */);
	}


	// Use the fact that explicitly requesting 0 width (%0s) results in UB and
	// interpret width == 0 as "no width requested":
	// width == 0 - no width requested
	// width < 0 - left-justify s within and pad it to -width chars, if necessary
	// width > 0 - right-justify s, not implemented yet
	static int AppendString(char *buff, const char buff_end, int width,
	int max_chars, const char *s) {
	if (!s)
	s = "<null>";
	int result = 0;
	for (; *s; s++) {
	if (max_chars >= 0 && result >= max_chars)
	break;
	result += AppendChar(buff, buff_end, *s);
	}
	// Only the left justified strings are supported.
	while (width < -result)
	result += AppendChar(buff, buff_end, ' ');
	return result;
	}

	static int AppendPointer(char *buff, const char buff_end, u64 ptr_value) {
	int result = 0;
	result += AppendString(buff, buff_end, 0, -1, "0x");
	result += AppendUnsigned(buff, buff_end, ptr_value, 16,
	SANITIZER_POINTER_FORMAT_LENGTH,
	true /* pad_with_zero /, false / uppercase */);
	return result;
	}

	int VSNPrintf(char *buff, int buff_length,
	const char *format, va_list args) {
	static const char *kPrintfFormatsHelp =
	"Supported Printf formats: %([0-9]*)?(z\|l\|ll)?{d,u,x,X}; %p; "
	"%[-]([0-9])?(\\.\\)?s; %c\nProvided format: ";
	RAW_CHECK(format);
	RAW_CHECK(buff_length > 0);
	const char *buff_end = &buff[buff_length - 1];
	const char *cur = format;
	int result = 0;
	for (; *cur; cur++) {
	if (*cur != '%') {
	result += AppendChar(&buff, buff_end, *cur);
	continue;
	}
	cur++;
	bool left_justified = *cur == '-';
	if (left_justified)
	cur++;
	bool have_width = (cur >= '0' && cur <= '9');
	bool pad_with_zero = (*cur == '0');
	int width = 0;
	if (have_width) {
	while (cur >= '0' && cur <= '9') {
	width = width * 10 + *cur++ - '0';
	}
	}
	bool have_precision = (cur[0] == '.' && cur[1] == '*');
	int precision = -1;
	if (have_precision) {
	cur += 2;
	precision = va_arg(args, int);
	}
	bool have_z = (*cur == 'z');
	cur += have_z;
	bool have_l = cur[0] == 'l' && cur[1] != 'l';
	cur += have_l;
	bool have_ll = cur[0] == 'l' && cur[1] == 'l';
	cur += have_ll * 2;
	const bool have_length = have_z \|\| have_l \|\| have_ll;
	const bool have_flags = have_width \|\| have_length;
	// At the moment only %s supports precision and left-justification.
	CHECK(!((precision >= 0 \|\| left_justified) && *cur != 's'));
	switch (*cur) {
	case 'd': {
	s64 dval = have_ll ? va_arg(args, s64)
	: have_z ? va_arg(args, sptr)
	: have_l ? va_arg(args, long)
	: va_arg(args, int);
	result += AppendSignedDecimal(&buff, buff_end, dval, width,
	pad_with_zero);
	break;
	}
	case 'u':
	case 'x':
	case 'X': {
	u64 uval = have_ll ? va_arg(args, u64)
	: have_z ? va_arg(args, uptr)
	: have_l ? va_arg(args, unsigned long)
	: va_arg(args, unsigned);
	bool uppercase = (*cur == 'X');
	result += AppendUnsigned(&buff, buff_end, uval, (*cur == 'u') ? 10 : 16,
	width, pad_with_zero, uppercase);
	break;
	}
	case 'p': {
	RAW_CHECK_VA(!have_flags, kPrintfFormatsHelp, format);
	result += AppendPointer(&buff, buff_end, va_arg(args, uptr));
	break;
	}
	case 's': {
	RAW_CHECK_VA(!have_length, kPrintfFormatsHelp, format);
	// Only left-justified width is supported.
	CHECK(!have_width \|\| left_justified);
	result += AppendString(&buff, buff_end, left_justified ? -width : width,
	precision, va_arg(args, char*));
	break;
	}
	case 'c': {
	RAW_CHECK_VA(!have_flags, kPrintfFormatsHelp, format);
	result += AppendChar(&buff, buff_end, va_arg(args, int));
	break;
	}
	case '%' : {
	RAW_CHECK_VA(!have_flags, kPrintfFormatsHelp, format);
	result += AppendChar(&buff, buff_end, '%');
	break;
	}
	default: {
	RAW_CHECK_VA(false, kPrintfFormatsHelp, format);
	}
	}
	}
	RAW_CHECK(buff <= buff_end);
	AppendChar(&buff, buff_end + 1, '\0');
	return result;
	}

	static void (PrintfAndReportCallback)(const char );
	void SetPrintfAndReportCallback(void (callback)(const char )) {
	PrintfAndReportCallback = callback;
	}

	// Can be overriden in frontend.
	#if SANITIZER_GO && defined(TSAN_EXTERNAL_HOOKS)
	// Implementation must be defined in frontend.
	extern "C" void __sanitizer_on_print(const char *str);
	#else
	SANITIZER_INTERFACE_WEAK_DEF(void, __sanitizer_on_print, const char *str) {
	(void)str;
	}
	#endif

	static void CallPrintfAndReportCallback(const char *str) {
	__sanitizer_on_print(str);
	if (PrintfAndReportCallback)
	PrintfAndReportCallback(str);
	}

	static void NOINLINE SharedPrintfCodeNoBuffer(bool append_pid,
	char *local_buffer,
	int buffer_size,
	const char *format,
	va_list args) {
	va_list args2;
	va_copy(args2, args);
	InternalMmapVector<char> v;
	int needed_length = 0;
	char *buffer = local_buffer;
	// First try to print a message using a local buffer, and then fall back to
	// mmaped buffer.
	for (int use_mmap = 0;; use_mmap++) {
	if (use_mmap) {
	va_end(args);
	va_copy(args, args2);
	v.resize(needed_length + 1);
	buffer_size = v.capacity();
	v.resize(buffer_size);
	buffer = &v[0];
	}
	needed_length = 0;
	// Fuchsia's logging infrastructure always keeps track of the logging
	// process, thread, and timestamp, so never prepend such information.
	if (!SANITIZER_FUCHSIA && append_pid) {
	int pid = internal_getpid();
	const char *exe_name = GetProcessName();
	if (common_flags()->log_exe_name && exe_name) {
	needed_length += internal_snprintf(buffer, buffer_size,
	"==%s", exe_name);
	if (needed_length >= buffer_size)
	continue;
	}
	needed_length += internal_snprintf(
	buffer + needed_length, buffer_size - needed_length, "==%d==", pid);
	if (needed_length >= buffer_size)
	continue;
	}
	needed_length += VSNPrintf(buffer + needed_length,
	buffer_size - needed_length, format, args);
	if (needed_length >= buffer_size)
	continue;
	// If the message fit into the buffer, print it and exit.
	break;
	}
	RawWrite(buffer);

	// Remove color sequences from the message.
	RemoveANSIEscapeSequencesFromString(buffer);
	CallPrintfAndReportCallback(buffer);
	LogMessageOnPrintf(buffer);

	va_end(args2);
	}

	static void NOINLINE SharedPrintfCode(bool append_pid, const char *format,
	va_list args) {
	// \|local_buffer\| is small enough not to overflow the stack and/or violate
	// the stack limit enforced by TSan (-Wframe-larger-than=512). On the other
	// hand, the bigger the buffer is, the more the chance the error report will
	// fit into it.
	char local_buffer[400];
	SharedPrintfCodeNoBuffer(append_pid, local_buffer, ARRAY_SIZE(local_buffer),
	format, args);
	}

	void Printf(const char *format, ...) {
	va_list args;
	va_start(args, format);
	SharedPrintfCode(false, format, args);
	va_end(args);
	}

	// Like Printf, but prints the current PID before the output string.
	void Report(const char *format, ...) {
	va_list args;
	va_start(args, format);
	SharedPrintfCode(true, format, args);
	va_end(args);
	}

	// Writes at most "length" symbols to "buffer" (including trailing '\0').
	// Returns the number of symbols that should have been written to buffer
	// (not including trailing '\0'). Thus, the string is truncated
	// iff return value is not less than "length".
	int internal_snprintf(char buffer, uptr length, const char format, ...) {
	va_list args;
	va_start(args, format);
	int needed_length = VSNPrintf(buffer, length, format, args);
	va_end(args);
	return needed_length;
	}

	void InternalScopedString::append(const char *format, ...) {
	uptr prev_len = length();

	while (true) {
	buffer_.resize(buffer_.capacity());

	va_list args;
	va_start(args, format);
	uptr sz = VSNPrintf(buffer_.data() + prev_len, buffer_.size() - prev_len,
	format, args);
	va_end(args);
	if (sz < buffer_.size() - prev_len) {
	buffer_.resize(prev_len + sz + 1);
	break;
	}

	buffer_.reserve(buffer_.capacity() * 2);
	}
	CHECK_EQ(buffer_[length()], '\0');
	}

	} // namespace __sanitizer