为什么我的指针会改变？（裸机）

Question

我在裸机应用程序中遇到内存问题。

我在 C 文件中有 2 个全局变量：

int var = 1;
int *p_var = &(var);

同一个文件有一个函数（IRQ 处理程序），其中下列语句为真：

var == 1
*p_var != var

期望的行为：*p_var 不应该等于 var 吗？

感谢任何帮助！

更新： 感谢您到目前为止的回复。

由于问题出在内存中，这里是我的代码的一些相关部分：

这是我的切入点。也许el1_entry不好？

#include "mm.h"
#include "arm/sysreg.h"

.section ".text.boot"

.globl _start
_start:
    mrs x0, mpidr_el1   // Get info about the CPU from reg mpidr_el1
    and x0, x0, #0xFF   // Extract the ID of the CPU
    cmp x0, #0          // Comopare the id of the CPU core with 0
    beq master          // If the core's id == 0, branch to mater
    b proc_hang         // If the core' id != 0, branch to hang


master:
    // Disable the MMU
    ldr    x0, =SCTLR_VALUE_MMU_DISABLED
    msr    sctlr_el1, x0

    // EL1 will execute at Aarch64
    ldr    x0, =HCR_VALUE
    msr    hcr_el2, x0

    // EL1 will execute at Aarch64; and EL0 and 1 will be "non secure"
    ldr    x0, =SCR_VALUE
    msr    scr_el3, x0

    
    // Configure EL1 to use its own stack and disable interrupts when EL1 
    ldr    x0, =SPSR_VALUE
    msr    spsr_el3, x0

    // Jump to el1_entry
    adr    x0, el1_entry        
    msr    elr_el3, x0
    eret  

el1_entry:
    /* Clean memory from addresses bss_begin to bss_end */
    adr x0, bss_begin
    ldr x1, =bss_end
    sub x1, x1, x0
     bl memzero          // Call function to clean memory

    mov sp, #LOW_MEMORY // Initialize stack pointer
    bl kernel_main      // Transfer control to kernel_main function
    b proc_hang

proc_hang:
    b proc_hang

向量table，在中断之间保存和恢复状态。也许保存和恢复有问题？

#include "entry.h"

/* Macro to save EL1 state when an exception happens */
.macro  kernel_entry
    sub sp, sp, #S_FRAME_SIZE
    stp x0, x1, [sp, #16 * 0]
    stp x2, x3, [sp, #16 * 1]
    stp x4, x5, [sp, #16 * 2]
    stp x6, x7, [sp, #16 * 3]
    stp x8, x9, [sp, #16 * 4]
    stp x10, x11, [sp, #16 * 5]
    stp x12, x13, [sp, #16 * 6]
    stp x14, x15, [sp, #16 * 7]
    stp x16, x17, [sp, #16 * 8]
    stp x18, x19, [sp, #16 * 9]
    stp x20, x21, [sp, #16 * 10]
    stp x22, x23, [sp, #16 * 11]
    stp x24, x25, [sp, #16 * 12]
    stp x26, x27, [sp, #16 * 13]
    stp x28, x29, [sp, #16 * 14]

    mrs x22, elr_el1
    mrs x23, spsr_el1

    stp x30, x22, [sp, #16 * 15] 
    str x23, [sp, #16 * 16]
.endm

/* Macro to restore EL1 state and return from the exception handling */
.macro  kernel_exit
    ldr x23, [sp, #16 * 16]
    ldp x30, x22, [sp, #16 * 15] 

    msr elr_el1, x22            
    msr spsr_el1, x23

    ldp x0, x1, [sp, #16 * 0]
    ldp x2, x3, [sp, #16 * 1]
    ldp x4, x5, [sp, #16 * 2]
    ldp x6, x7, [sp, #16 * 3]
    ldp x8, x9, [sp, #16 * 4]
    ldp x10, x11, [sp, #16 * 5]
    ldp x12, x13, [sp, #16 * 6]
    ldp x14, x15, [sp, #16 * 7]
    ldp x16, x17, [sp, #16 * 8]
    ldp x18, x19, [sp, #16 * 9]
    ldp x20, x21, [sp, #16 * 10]
    ldp x22, x23, [sp, #16 * 11]
    ldp x24, x25, [sp, #16 * 12]
    ldp x26, x27, [sp, #16 * 13]
    ldp x28, x29, [sp, #16 * 14]
    add sp, sp, #S_FRAME_SIZE       
    eret
.endm


/*
 * Exception vectors table is initialized in this file..., but I'm not including the code in this post.
 */
 ...


// IRQ Handler
el1_irq:
    kernel_entry 
    bl  handle_irq
    kernel_exit

handle_irq

...
void handle_irq(void) {
    u32 irq;

    irq = REGS_IRQ->irq0_pending_0;

    while(irq) {
        if(irq & SYS_TIMER_IRQ_1) {
            irq &= ~SYS_TIMER_IRQ_1;
            handle_timer_1();
        }
    }

}

handle_timer_1

...
void handle_timer_1(void)
{
    // Set the next timer interrupt
    currrent_value_1 += interval_1;
    REGS_TIMER->compare[1] = currrent_value_1;
    REGS_TIMER->control_status |= SYS_TIMER_IRQ_1;
    
    timer_tick();
}

timer_tick()（观察到意外行为）

...
int var = 1;
int *p_var = &(var);      // Current task being executed

void timer_tick(void)
{
    char buff[] = "0000000000000000";

    parse_int(*p_var, buff, 16);
    uart_send_string("*p_var: ");
    uart_send_string(buff);
    uart_send_string("\n");

    parse_int(var, buff, 16);
    uart_send_string("var: ");
    uart_send_string(buff);
    uart_send_string("\n");

    if(p_var == &var) {
        uart_send_string("equal: true");
    } else {
        uart_send_string("equal: false");
    }
}

“最小示例”有点泛泛，所以我不能直接在此处 post。我把它放在 github （我链接到入口点）

Answer 1

Am I messing up with memory elsewhere without realizing?

是的。

为什么我的指针会改变？（裸机）

Why are my pointers changing? (bare metal)

c

assembly

embedded

arm64

bare-metal

为什么我的指针会改变？ （裸机）

Why are my pointers changing? (bare metal)

c

assembly

embedded

arm64

bare-metal

为什么我的指针会改变？（裸机）