AVR 的 __brkval 是什么，它在哪里定义？
What is __brkval for AVR, and where is it defined?
我在https://playground.arduino.cc/Code/AvailableMemory中看到了freeMemory函数，它似乎使用了一个叫做__brkval的东西。但是，我根本找不到这个宏或变量定义在哪里：
$ grep -ri brkval /c/arduino-1.8.8/ --include='*.c' --include='*.h'
/c/arduino-1.8.8/libraries/Robot_Control/src/Fat16util.h: extern int* __brkval;
/c/arduino-1.8.8/libraries/Robot_Control/src/Fat16util.h: if (reinterpret_cast<int>(__brkval) == 0) {
/c/arduino-1.8.8/libraries/Robot_Control/src/Fat16util.h: - reinterpret_cast<int>(__brkval);
/c/arduino-1.8.8/libraries/SD/src/utility/SdFatUtil.h: extern int* __brkval;
/c/arduino-1.8.8/libraries/SD/src/utility/SdFatUtil.h: if (reinterpret_cast<int>(__brkval) == 0) {
/c/arduino-1.8.8/libraries/SD/src/utility/SdFatUtil.h: - reinterpret_cast<int>(__brkval);
$ grep -ri brkval /c/avr-gcc-8.2.0-x64-mingw/ --include='*.c' --include='*.h'
# nothing
$ grep -ri brkval /c/Program\ Files\ \(x86\)/Atmel/Studio/ --include='*.c' --include='*.h'
# nothing
$ grep -ri brkval /c/cvavr/ --include='*.c'
# nothing
也就是说，只有Arduino IDE有一些引用，但只是作为extern int*引用，没有定义。
最接近我的某种冗长解释来自 https://github.com/greiman/SdFat/blob/master/src/FreeStack.h :
/** boundary between stack and heap. */
extern char *__brkval;
...但同样，没有定义。
那么这个变量或者宏是在哪里定义的呢？
编辑：根据评论，搜索所有文件：
$ grep -ri brkval /c/cvavr/
# nothing
$ grep -ri brkval /c/Program\ Files\ \(x86\)/Atmel/Studio/
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/avr25/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/avr25/tiny-stack/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/avr3/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/avr31/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/avr35/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/avr4/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/avr5/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/avr51/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/avr6/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/avrtiny/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/avrxmega2/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/avrxmega3/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/avrxmega3/short-calls/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/avrxmega4/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/avrxmega5/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/avrxmega6/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/avrxmega7/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/tiny-stack/libc.a matches
/c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/doc/avr-libc/avr-libc-user-manual/stdlib__private_8h_source.html:<a name="l00045"></a>00045 <span class="keyword">extern</span> <span class="keywordtype">char</span> *__brkval; <span class="comment">/* first location not yet allocated */</span>
$ grep -ri brkval /c/avr-gcc-8.2.0-x64-mingw/
Binary file /c/avr-gcc-8.2.0-x64-mingw/avr/lib/avr25/libc.a matches
Binary file /c/avr-gcc-8.2.0-x64-mingw/avr/lib/avr25/tiny-stack/libc.a matches
Binary file /c/avr-gcc-8.2.0-x64-mingw/avr/lib/avr3/libc.a matches
Binary file /c/avr-gcc-8.2.0-x64-mingw/avr/lib/avr31/libc.a matches
Binary file /c/avr-gcc-8.2.0-x64-mingw/avr/lib/avr35/libc.a matches
Binary file /c/avr-gcc-8.2.0-x64-mingw/avr/lib/avr4/libc.a matches
Binary file /c/avr-gcc-8.2.0-x64-mingw/avr/lib/avr5/libc.a matches
Binary file /c/avr-gcc-8.2.0-x64-mingw/avr/lib/avr51/libc.a matches
Binary file /c/avr-gcc-8.2.0-x64-mingw/avr/lib/avr6/libc.a matches
Binary file /c/avr-gcc-8.2.0-x64-mingw/avr/lib/avrtiny/libc.a matches
Binary file /c/avr-gcc-8.2.0-x64-mingw/avr/lib/avrxmega2/libc.a matches
Binary file /c/avr-gcc-8.2.0-x64-mingw/avr/lib/avrxmega4/libc.a matches
Binary file /c/avr-gcc-8.2.0-x64-mingw/avr/lib/avrxmega5/libc.a matches
Binary file /c/avr-gcc-8.2.0-x64-mingw/avr/lib/avrxmega6/libc.a matches
Binary file /c/avr-gcc-8.2.0-x64-mingw/avr/lib/avrxmega7/libc.a matches
Binary file /c/avr-gcc-8.2.0-x64-mingw/avr/lib/libc.a matches
Binary file /c/avr-gcc-8.2.0-x64-mingw/avr/lib/tiny-stack/libc.a matches
$ grep -ri brkval /c/arduino-1.8.8/
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/avr25/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/avr25/tiny-stack/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/avr3/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/avr31/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/avr35/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/avr4/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/avr5/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/avr51/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/avr6/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/avrtiny/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/avrxmega2/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/avrxmega3/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/avrxmega3/short-calls/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/avrxmega4/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/avrxmega5/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/avrxmega6/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/avrxmega7/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/tiny-stack/libc.a matches
/c/arduino-1.8.8/libraries/Robot_Control/src/Fat16util.h: extern int* __brkval;
/c/arduino-1.8.8/libraries/Robot_Control/src/Fat16util.h: if (reinterpret_cast<int>(__brkval) == 0) {
/c/arduino-1.8.8/libraries/Robot_Control/src/Fat16util.h: - reinterpret_cast<int>(__brkval);
/c/arduino-1.8.8/libraries/SD/src/utility/SdFatUtil.h: extern int* __brkval;
/c/arduino-1.8.8/libraries/SD/src/utility/SdFatUtil.h: if (reinterpret_cast<int>(__brkval) == 0) {
/c/arduino-1.8.8/libraries/SD/src/utility/SdFatUtil.h: - reinterpret_cast<int>(__brkval);
还有很多人有同样的问题。正如所指出的那样，用最简单的术语来说，它用于标记堆栈和堆内存之间的边界。以下是一些相关讨论，内容包括 __brkval:
- Arduino: Question about memory allocation analysis。
- Free Memory Questions, Arduino。
- Arduino:You know you have a memory problem when...。
- AVRGCC: Monitoring stack usage。
- Arduino Playground: CorruptArrayVariablesAndMemory。
最后的 link 解决了您的主要问题，至少对于 Arduino 环境而言：
with the memory profiler function added (note that it uses freeMemory via MemoryFree.h, which is also given in the thread above), and starting array size of 100 elements (400 bytes):
// minitest.pde
static unsigned long mydata_count;
static const long SERSPEED=115200;
static const int SIZE=100;
static const char RSTSTR[] = "RESET!!";
static unsigned long mydata[SIZE];
#include <MemoryFree.h>
extern unsigned int __data_start;
extern unsigned int __data_end;
extern unsigned int __bss_start;
extern unsigned int __bss_end;
extern unsigned int __heap_start;
//extern void *__malloc_heap_start; --> apparently already declared as char*
//extern void *__malloc_margin; --> apparently already declared as a size_t
extern void *__brkval;
我在https://playground.arduino.cc/Code/AvailableMemory中看到了freeMemory函数，它似乎使用了一个叫做__brkval的东西。但是，我根本找不到这个宏或变量定义在哪里：
$ grep -ri brkval /c/arduino-1.8.8/ --include='*.c' --include='*.h'
/c/arduino-1.8.8/libraries/Robot_Control/src/Fat16util.h: extern int* __brkval;
/c/arduino-1.8.8/libraries/Robot_Control/src/Fat16util.h: if (reinterpret_cast<int>(__brkval) == 0) {
/c/arduino-1.8.8/libraries/Robot_Control/src/Fat16util.h: - reinterpret_cast<int>(__brkval);
/c/arduino-1.8.8/libraries/SD/src/utility/SdFatUtil.h: extern int* __brkval;
/c/arduino-1.8.8/libraries/SD/src/utility/SdFatUtil.h: if (reinterpret_cast<int>(__brkval) == 0) {
/c/arduino-1.8.8/libraries/SD/src/utility/SdFatUtil.h: - reinterpret_cast<int>(__brkval);
$ grep -ri brkval /c/avr-gcc-8.2.0-x64-mingw/ --include='*.c' --include='*.h'
# nothing
$ grep -ri brkval /c/Program\ Files\ \(x86\)/Atmel/Studio/ --include='*.c' --include='*.h'
# nothing
$ grep -ri brkval /c/cvavr/ --include='*.c'
# nothing
也就是说，只有Arduino IDE有一些引用，但只是作为extern int*引用，没有定义。
最接近我的某种冗长解释来自 https://github.com/greiman/SdFat/blob/master/src/FreeStack.h :
/** boundary between stack and heap. */
extern char *__brkval;
...但同样，没有定义。
那么这个变量或者宏是在哪里定义的呢？
编辑：根据评论，搜索所有文件：
$ grep -ri brkval /c/cvavr/
# nothing
$ grep -ri brkval /c/Program\ Files\ \(x86\)/Atmel/Studio/
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/avr25/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/avr25/tiny-stack/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/avr3/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/avr31/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/avr35/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/avr4/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/avr5/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/avr51/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/avr6/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/avrtiny/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/avrxmega2/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/avrxmega3/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/avrxmega3/short-calls/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/avrxmega4/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/avrxmega5/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/avrxmega6/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/avrxmega7/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/tiny-stack/libc.a matches
/c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/doc/avr-libc/avr-libc-user-manual/stdlib__private_8h_source.html:<a name="l00045"></a>00045 <span class="keyword">extern</span> <span class="keywordtype">char</span> *__brkval; <span class="comment">/* first location not yet allocated */</span>
$ grep -ri brkval /c/avr-gcc-8.2.0-x64-mingw/
Binary file /c/avr-gcc-8.2.0-x64-mingw/avr/lib/avr25/libc.a matches
Binary file /c/avr-gcc-8.2.0-x64-mingw/avr/lib/avr25/tiny-stack/libc.a matches
Binary file /c/avr-gcc-8.2.0-x64-mingw/avr/lib/avr3/libc.a matches
Binary file /c/avr-gcc-8.2.0-x64-mingw/avr/lib/avr31/libc.a matches
Binary file /c/avr-gcc-8.2.0-x64-mingw/avr/lib/avr35/libc.a matches
Binary file /c/avr-gcc-8.2.0-x64-mingw/avr/lib/avr4/libc.a matches
Binary file /c/avr-gcc-8.2.0-x64-mingw/avr/lib/avr5/libc.a matches
Binary file /c/avr-gcc-8.2.0-x64-mingw/avr/lib/avr51/libc.a matches
Binary file /c/avr-gcc-8.2.0-x64-mingw/avr/lib/avr6/libc.a matches
Binary file /c/avr-gcc-8.2.0-x64-mingw/avr/lib/avrtiny/libc.a matches
Binary file /c/avr-gcc-8.2.0-x64-mingw/avr/lib/avrxmega2/libc.a matches
Binary file /c/avr-gcc-8.2.0-x64-mingw/avr/lib/avrxmega4/libc.a matches
Binary file /c/avr-gcc-8.2.0-x64-mingw/avr/lib/avrxmega5/libc.a matches
Binary file /c/avr-gcc-8.2.0-x64-mingw/avr/lib/avrxmega6/libc.a matches
Binary file /c/avr-gcc-8.2.0-x64-mingw/avr/lib/avrxmega7/libc.a matches
Binary file /c/avr-gcc-8.2.0-x64-mingw/avr/lib/libc.a matches
Binary file /c/avr-gcc-8.2.0-x64-mingw/avr/lib/tiny-stack/libc.a matches
$ grep -ri brkval /c/arduino-1.8.8/
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/avr25/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/avr25/tiny-stack/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/avr3/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/avr31/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/avr35/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/avr4/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/avr5/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/avr51/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/avr6/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/avrtiny/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/avrxmega2/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/avrxmega3/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/avrxmega3/short-calls/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/avrxmega4/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/avrxmega5/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/avrxmega6/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/avrxmega7/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/tiny-stack/libc.a matches
/c/arduino-1.8.8/libraries/Robot_Control/src/Fat16util.h: extern int* __brkval;
/c/arduino-1.8.8/libraries/Robot_Control/src/Fat16util.h: if (reinterpret_cast<int>(__brkval) == 0) {
/c/arduino-1.8.8/libraries/Robot_Control/src/Fat16util.h: - reinterpret_cast<int>(__brkval);
/c/arduino-1.8.8/libraries/SD/src/utility/SdFatUtil.h: extern int* __brkval;
/c/arduino-1.8.8/libraries/SD/src/utility/SdFatUtil.h: if (reinterpret_cast<int>(__brkval) == 0) {
/c/arduino-1.8.8/libraries/SD/src/utility/SdFatUtil.h: - reinterpret_cast<int>(__brkval);
还有很多人有同样的问题。正如所指出的那样，用最简单的术语来说，它用于标记堆栈和堆内存之间的边界。以下是一些相关讨论，内容包括 __brkval:
- Arduino: Question about memory allocation analysis。
- Free Memory Questions, Arduino。
- Arduino:You know you have a memory problem when...。
- AVRGCC: Monitoring stack usage。
- Arduino Playground: CorruptArrayVariablesAndMemory。
最后的 link 解决了您的主要问题，至少对于 Arduino 环境而言：
with the memory profiler function added (note that it uses freeMemory via MemoryFree.h, which is also given in the thread above), and starting array size of 100 elements (400 bytes):
// minitest.pde
static unsigned long mydata_count;
static const long SERSPEED=115200;
static const int SIZE=100;
static const char RSTSTR[] = "RESET!!";
static unsigned long mydata[SIZE];
#include <MemoryFree.h>
extern unsigned int __data_start;
extern unsigned int __data_end;
extern unsigned int __bss_start;
extern unsigned int __bss_end;
extern unsigned int __heap_start;
//extern void *__malloc_heap_start; --> apparently already declared as char*
//extern void *__malloc_margin; --> apparently already declared as a size_t
extern void *__brkval;