编译使用O2优化后程序起不来，GDB报signal trap，如果打断点到rt_hw_board_init处，又没有问题

发布于 2022-12-13 15:41:24 浏览：535 订阅该版

[tocm]

使用的是GD32W51x的芯片，不优化没有问题，开启O1、O2或Og优化就会单板起不来。

如果不打断点gdb跟上去，会有各种不同的错误调用栈，但都会报`signal trap`。

如果在rt_hw_board_init开始处打断点，gdb跟上去运行，就可以正常启动。

看了下汇编，水平有限，也没看出啥问题：

1、启动.s调用entry()函数
```
Zerobss:
  ldr r3, = _ebss
 8006cc8:	4b08      	ldr	r3, [pc, #32]	; (8006cec <LoopForever+0x12>)
  cmp r2, r3
 8006cca:	429a      	cmp	r2, r3
  bcc FillZerobss
 8006ccc:	d3f9      	bcc.n	8006cc2 <FillZerobss>
/* Call SystemInit function */
  bl  SystemInit
 8006cce:	f7fb f867 	bl	8001da0 <SystemInit>
/* Call static constructors */
    bl __libc_init_array
 8006cd2:	f00a fcbd 	bl	8011650 <__libc_init_array>
/* Call the application's entry point.*/
  bl  entry
 8006cd6:	f000 fbab 	bl	8007430 <entry>
```

2、在entry函数中调用各初始化函数，优化掉了对rtthread_startup的调用
```
08007430 <entry>:
{
 8007430:	b508      	push	{r3, lr}
 * @brief  This function will call all levels of initialization functions to complete
 *         the initialization of the system, and finally start the scheduler.
 */
int rtthread_startup(void)
{
    rt_hw_interrupt_disable();
 8007432:	f7f8 fed1 	bl	80001d8 <rt_hw_interrupt_disable>

/* board level initialization
     * NOTE: please initialize heap inside board initialization.
     */
    rt_hw_board_init();
 8007436:	f7ff fc5d 	bl	8006cf4 <rt_hw_board_init>

/* show RT-Thread version */
    rt_show_version();
 800743a:	f008 fbaf 	bl	800fb9c <rt_show_version>

/* timer system initialization */
    rt_system_timer_init();
 800743e:	f001 fa45 	bl	80088cc <rt_system_timer_init>
```

3、对于rt_hw_board_init函数的调用：
```
void icache_enable()
{
    if (ENABLE != (ICACHE_CTL & ICACHE_CTL_EN))
 8006cf4:	4b15      	ldr	r3, [pc, #84]	; (8006d4c <rt_hw_board_init+0x58>)

/**
 * This function will initial your board.
 */
void rt_hw_board_init()
{
 8006cf6:	b510      	push	{r4, lr}
    if (ENABLE != (ICACHE_CTL & ICACHE_CTL_EN))
 8006cf8:	681a      	ldr	r2, [r3, #0]
 8006cfa:	07d2      	lsls	r2, r2, #31
 8006cfc:	d403      	bmi.n	8006d06 <rt_hw_board_init+0x12>
        ICACHE_CTL |= ICACHE_CTL_EN;
 8006cfe:	681a      	ldr	r2, [r3, #0]
 8006d00:	f042 0201 	orr.w	r2, r2, #1
 8006d04:	601a      	str	r2, [r3, #0]
    /* Enable icache to run quickly */
    icache_enable();

/* System Clock Update */
    SystemCoreClockUpdate();
 8006d06:	f7fb f8d5 	bl	8001eb4 <SystemCoreClockUpdate>
```

以下是rtconfig.py中对于gcc编译选项的设置：
```
DEVICE = ' -mcpu=cortex-m33 -mthumb -mfpu=fpv5-sp-d16 -mfloat-abi=hard -ffunction-sections -fdata-sections'
    CFLAGS = DEVICE + ' -Dgcc' + ' -DSOC_SERIES_' + BOARD
    AFLAGS = ' -c' + DEVICE + ' -x assembler-with-cpp -Wa,-mimplicit-it=thumb '
    LFLAGS = DEVICE + ' -Wl,--gc-sections, -Wl,-cref,-u,Reset_Handler -T board/linker_scripts/link.ld'

CPATH = ''
    LPATH = ''

# distinguish debug and release version
    if BUILD == 'debug':
        CFLAGS += ' -O0 -gdwarf-2 -g'
        AFLAGS += ' -gdwarf-2'
    else:
        CFLAGS += ' -O2 -gdwarf-2 -g'
        AFLAGS += ' -gdwarf-2'

CFLAGS += ' -Wall -Wno-unused-parameter -Wno-unused-function'
    CXXFLAGS = CFLAGS
```