c - gcc 在优化期间更改映射变量的地址

Question

我正在开源环境中使用arm-none-eabi-gcc v4.9.3 为ARM stm32 微 Controller 编译C 代码。 代码无需编译器优化即可正常运行(gcc -g -O0 ...)。

当我启用哪怕最轻微的优化(gcc -g -O1 ...)时，链接器定义的变量的地址都会更改。

文件内存.ld

register_cortexm3_ACTLR      = 0xe000e008;
...

MEMORY
{
                 rom (rx ) : ORIGIN = 0x08000000,  LENGTH = 256K
                 ram (rxw) : ORIGIN = 0x20000000,  LENGTH = 64K
        sram_bitband (rw ) : ORIGIN = 0x22000000,  LENGTH = 32768K
          peripheral (rw ) : ORIGIN = 0x40000000,  LENGTH = 1024K
  peripheral_bitband (rw ) : ORIGIN = 0x42000000,  LENGTH = 32768K
                sram (rwx) : ORIGIN = 0x60000000,  LENGTH = 1048576K
        ram_external (rwx) : ORIGIN = 0x60000000,  LENGTH = 1048576K
                code (rwx) : ORIGIN = 0x60000000,  LENGTH = 1048576K
     device_external (rw ) : ORIGIN = 0xa0000000,  LENGTH = 1048576K
  private_peripheral (rw ) : ORIGIN = 0xe0000000,  LENGTH = 1024K
       vendor_memory (rw ) : ORIGIN = 0xe0100000,  LENGTH = 523264K
}

SECTIONS
{
 /* Section for variables mapped onto registers */
 .peripherals (OVERLAY) :
 {
    . = ALIGN(4);
    *(.peripherals)
 } >peripheral

 .private_peripherals (OVERLAY) :
 {
    . = ALIGN(4);
    *(.private_peripherals)
} >private_peripheral

...

文件register_cortexm3.h

typedef struct {
    unsigned DISMCYCINT  : 1;
    unsigned DISDEFWBUF  : 1;
    unsigned DISFOLD     : 1;
    unsigned reserved1   : 13;
    unsigned reserved2   : 16;
} __attribute__( ( __packed__ ) ) register_cortexm3_actlr_t;

...

文件register_cortexm3.c

void check_same( volatile void* Address1, volatile void* Address2 ) {

    if ( Address1 != Address2 )
    { Assert_Halt_EC( ec_InvalidImplementation ); }
}

volatile register_cortexm3_actlr_t register_cortexm3_ACTLR   
__attribute__( ( section( ".private_peripherals" ) ) ); 

void register_cortexm3_prepare() {

    // checking for correct linker script settings
    check_same(&( register_cortexm3_ACTLR ), ( volatile void* ) 0xe000e008);
}

---

当启用优化时，上述比较失败，因为在 check_same() 函数内部，根据 gdb，第一个参数是 0xe0000000(其内存部分的起始地址):

Breakpoint 1, Assert_Halt_EC   (ErrorCode=ErrorCode@entry=ec_InvalidImplementation) at ttc-lib/ttc_basic.c:65
65      void Assert_Halt_EC( volatile ErrorCode_e ErrorCode ) { // block endless
(gdb) up
#1  0x08004440 in check_same (Address1=Address1@entry=0xe0000000, Address2=Address2@entry=0xe000e008) at ttc-lib/ttc_basic.c:58
58          { Assert_Halt_EC( ec_InvalidImplementation ); }
(gdb) up
#2  0x080034f6 in register_cortexm3_prepare () at ttc-lib/register/register_cortexm3.c:40
40          Assert_SameAddress( &( register_cortexm3_ACTLR ), ( void* ) 0xe000e008 );
(gdb) x &( register_cortexm3_ACTLR )
0xe000e008:     0x00000000

正如您在最后一个 gdb 输出行中看到的，gdb 知道 register_cortexm3_ACTLR 的正确地址。

这是 gcc 错误还是功能？ 如何解决这个问题？

Answer 1

我不确定为什么优化会对此产生任何影响，但基本问题是您给出了符号 register_cortexm3_ACTLR 的两个不同且相互冲突的定义。链接描述文件中的一个定义表示它位于任何节中的地址 0xe000e008，而 C 代码中的另一个定义表示它位于 .private_peripherals 节的某个偏移处。

您需要选择其中之一。如果您希望变量位于链接描述文件中给定的地址处，请使用 extern 来引用它。像这样的东西:

extern volatile register_cortexm3_actlr_t register_cortexm3_ACTLR;