newlib中malloc如何获取heap地址

newlib代码：

caddr_t
_sbrk (int incr)
{
extern char end asm (“end”); /* Defined by the linker. */
static char * heap_end;
char * prev_heap_end;

if (heap_end == NULL)
heap_end = & end;

prev_heap_end = heap_end;

if (heap_end + incr > stack_ptr)
{
/* Some of the libstdc+±v3 tests rely upon detecting
out of memory errors, so do not abort here. */
#if 0
extern void abort (void);

  _write (1, "_sbrk: Heap and stack collision\n", 32);
  
  abort ();

#else
errno = ENOMEM;
return (caddr_t) -1;
#endif
}

heap_end += incr;

return (caddr_t) prev_heap_end;
}

第一次调用使用end符号获取堆的起始地址，因此只需要在链接文件中在heap起始地址定义end标号即可。

.heap 0x00200000 (NOLOAD):
{
. = ALIGN(64);
__heap_start = .;
PROVIDE(end = .);
. = . + 0xA0000;
end = .;
}

如上，使用PROVIDE声明了end标号。

原文链接：https://blog.youkuaiyun.com/qq_14892521/article/details/118753374