c - Newlib 在 ARM 嵌入式系统中首次调用时无法分配堆

Question

我正在使用 gcc-arm-none-eabi 4.9 2014q4 为 Cortex-M4 编写裸机应用程序。当应用程序加载时，对 _sbrk 的第一次调用似乎无效。

我已经实现了 _sbrk 如下:

extern unsigned int _start_of_heap;
extern unsigned int _end_of_heap;
caddr_t heap = (caddr_t)&_start_of_heap;

#include "hardware/uart.h"

// low level bulk memory allocator - used by malloc
caddr_t _sbrk ( int increment ) {

    caddr_t prevHeap;
    caddr_t nextHeap;

    send_str("_sbrk(");
    send_dec(increment);
    send_str(")\n");

    prevHeap = heap;

    // Always return data aligned on a 8 byte boundary
    nextHeap = (caddr_t)(((unsigned int)(heap + increment) + 7) & ~7);

    // get current stack pointer
    register caddr_t stackPtr asm ("sp");

    send_str("\tstackPtr(");
    send_hex((uint32_t)stackPtr);
    send_str(")\n");
    send_str("\tprevHeap(");
    send_hex((uint32_t)prevHeap);
    send_str(")\n");

    // Check enough space and there is no collision with stack coming the other way
    // if stack is above start of heap
    if((nextHeap < stackPtr) && (nextHeap >= (caddr_t)&_start_of_heap) && (nextHeap < (caddr_t)&_end_of_heap)) {
        heap = nextHeap;
        return (caddr_t) prevHeap;
    }
    send_str("*\n");
    return NULL; // error - no more memory
}

链接器定义堆限制如下:

MEMORY
{
    SRAM_L (rwx) : ORIGIN = 0x00000000, LENGTH = 32K
    SRAM_U (rwx) : ORIGIN = 0x20000000, LENGTH = 32K
}

SECTIONS
{
    .vectors 0x00000000 :
    {
        *o(.vectors_)
    } >SRAM_L

    .text :
    {
        . = ALIGN (4);
        *(.text);
    } >SRAM_L

    . = . ;
    _datai = . ;
    .data :
    {
        . = ALIGN (4);
        _data = . ; *(.data .data.*); _edata = . ;
    } >SRAM_U AT >SRAM_L

    .data_init : 
    {
        _edatai = .;
    } >SRAM_L

    .bss :
    {
        . = ALIGN (4);
        _bss = . ; *(.bss) *(COMMON); _ebss = . ;
    } >SRAM_U

    . = ALIGN (4);
    . += 8;

    free_memory_start = .;
    _end_of_stack = .;
    end = .;
    _start_of_heap = .;
    . = 0x20007000;
    _start_of_stack = .;
    _end_of_heap = .;

}

程序代码运行快速堆栈和堆测试:

extern unsigned int _start_of_heap;
extern unsigned int _end_of_heap;
extern caddr_t heap;

void foo(uint8_t i)
{
    unsigned long blah = 0;
    unsigned long * halb;
    halb = malloc(sizeof(unsigned long));
    iprintf("blah(%08x) halb(%08x) heap(%08x)\n", &blah, halb, heap);

    if(i)
        foo(i - 1);

    free(halb);

}

int main(int argc, char ** argv)
{
    init_uart((void*)UART2_IPS_BASE_ADDR, 115200);

    iprintf("Heap test (%08x - %08x)\n", &_start_of_heap, &_end_of_heap);
    foo(10);
    return 0;

}

产生以下输出:

_sbrk(1040965006)             <----- Note large size
        stackPtr(20006E18)
        prevHeap(2000089C)
*                             <----- '*' indicates out of range
_sbrk(626)
        stackPtr(20006E18)
        prevHeap(2000089C)
Heap test (2000089c - 20007000)
blah(20006fb8) halb(00000410) heap(20000b10)
blah(20006fa0) halb(00000420) heap(20000b10)
blah(20006f88) halb(00000430) heap(20000b10)
blah(20006f70) halb(00000440) heap(20000b10)
blah(20006f58) halb(00000450) heap(20000b10)
blah(20006f40) halb(00000460) heap(20000b10)
blah(20006f28) halb(00000470) heap(20000b10)
blah(20006f10) halb(00000480) heap(20000b10)
blah(20006ef8) halb(00000490) heap(20000b10)
blah(20006ee0) halb(000004a0) heap(20000b10)
blah(20006ec8) halb(000004b0) heap(20000b10)

第一次分配是 1040965006 字节，这似乎不正确并且失败了。在此之后，我假设 malloc 继续分配 626 个字节。 halb 的每次后续调用 malloc 似乎都会返回一个超出我的堆栈范围的地址。这第一次调用看起来像错误，还是应该忽略它？如果是，malloc 返回的地址怎么了？

谢谢，德文

Answer 1

似乎某些变量可能未正确初始化。我已经更新了我的链接描述文件如下:

SECTIONS
{
    . = ORIGIN(SRAM_L);

    .vectors :
    {
        KEEP(*o(.vectors_))
    } >SRAM_L

    .text :
    {
        . = ALIGN(4);
        _start_text = .;
        *(.text)
        *(.text*)
        *(.rodata)
        *(.rodata*)
        _end_text = .;
    } >SRAM_L

        .ARM.extab :
        {
                *(.ARM.extab* .gnu.linkonce.armextab.*)
        } > SRAM_L

        __exidx_start = .;
        .ARM.exidx :
        {
                *(.ARM.exidx* .gnu.linkonce.armexidx.*)
        } > SRAM_L
        __exidx_end = .;

    _end_text = .;

    . = . ;
    _datai = . ;
    .data :
    {
        . = ALIGN (4);
        _data = . ; 
        *(.data)
        *(.data*)
        . = ALIGN (4);
        _edata = . ;
    } >SRAM_U AT >SRAM_L

    .data_init : 
    {
        _edatai = .;
    } >SRAM_L

    .bss :
    {
        . = ALIGN (4);
        _bss = . ; 
        *(.bss) 
        *(.bss*) 
        *(COMMON)
        . = ALIGN(4);
        _ebss = . ;
    } >SRAM_U

    . = ALIGN (4);
    . += 8;

    free_memory_start = .;
    _end_of_stack = .;
    PROVIDE(end = .);
    _start_of_heap = .;
    . = 0x20007000;
    _start_of_stack = .;
    _end_of_heap = .;

}

感谢sushihangover博文。