Difference between revisions of "How does Newlib initialize the heap?"
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== '''How does Newlib initialize the heap? (RL78, RX, ARM targets)''' == | == '''How does Newlib initialize the heap? (RL78, RX, ARM targets)''' == | ||
| − | When using the '''Newlib Library''', | + | When using the '''Newlib Library''', users must overwrite the _sbrk/sbrk_r function implemented in newlib. This is the function malloc() uses in order to define how much space is needed for an allocation. |
| − | + | Users of the '''Newlib-Nano Library''' must provide an implementation of the sbrk() function, since there is no default implementation included. | |
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Below are some examples of the default _sbrk function, depending on the toolchain used: | Below are some examples of the default _sbrk function, depending on the toolchain used: | ||
Latest revision as of 13:06, 13 January 2023
How does Newlib initialize the heap? (RL78, RX, ARM targets)
When using the Newlib Library, users must overwrite the _sbrk/sbrk_r function implemented in newlib. This is the function malloc() uses in order to define how much space is needed for an allocation.
Users of the Newlib-Nano Library must provide an implementation of the sbrk() function, since there is no default implementation included.
Below are some examples of the default _sbrk function, depending on the toolchain used:
RL78:
char *
_sbrk (int adj)
{
extern char end; //end of the bss section (start of heap)
static char * heap = & end;
char * rv = heap;
char * heaptop = (char *) &adj;
heap += adj;
/* The allocated chunk spans our stack? */
if (rv < heaptop && heap > heaptop
/* The allocated chunk spans our address space? */
|| heap < rv)
{
errno = ENOMEM;
return (char *) -1;
}
return rv;
}
RX:
extern void __set_heaptop (void * ptr);
char *
_sbrk (int adj)
{
extern char end;
static char * heap = & end;
char * rv = heap;
heap += adj;
__set_heaptop (heap);
return rv;
}
ARM:
register char * stack_ptr asm ("sp");
caddr_t __attribute__((weak))
_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;
}
These are the functions to overwrite if there is a need to set your own heap.
