Linux 转到u-boot命令提示符。您可以从那里使用u-boot命令检查内存，查看程序是否按预期工作，或者使用其他命令

但如果您想再次使用

go

，则必须重新启动u-boot。 从这里开始，如果您想在Allwinner平台上使用

go

，您可以修改回实现，以便u-boot在执行程序之前不会切换到

EL1

，并在您的系统上安装修改后的版本：

unsigned long do_go_exec(ulong (*entry)(int, char * const []), int argc,
             char *const argv[])
{
    int ret = 0;

    if (current_el() > 1) {
        smp_kick_all_cpus();
        dcache_disable();
        ret = entry(argc, argv);
    } else {
        printf("FAIL: current EL is not above or equal to EL1\n");
        ret = EINVAL;
    }
    return ret;
}

另一种方法是添加一个新的

go2

命令，该命令将使用上述实现

b） hello_world程序的启动代码不会根据ARM调用约定保留寄存器，更重要的是，它会按照一些ARM应用程序注释中的建议清除所有寄存器：

Disassembly of section .text:

0000000000000000 <_vector_table>:
       0:   1400024e    b   938 <_boot>
    ...
     200:   14000061    b   384 <SynchronousInterruptHandler>
    ...
     280:   14000082    b   488 <IRQInterruptHandler>
    ...
     300:   140000a1    b   584 <FIQInterruptHandler>
    ...
     380:   14000099    b   5e4 <SErrorInterruptHandler>


0000000000000938 <_boot>:
     938:   d2800000    mov x0, #0x0                    // #0
     93c:   d2800001    mov x1, #0x0                    // #0
     940:   d2800002    mov x2, #0x0                    // #0
     944:   d2800003    mov x3, #0x0                    // #0
     948:   d2800004    mov x4, #0x0                    // #0
     94c:   d2800005    mov x5, #0x0                    // #0
     950:   d2800006    mov x6, #0x0                    // #0
     954:   d2800007    mov x7, #0x0                    // #0
     958:   d2800008    mov x8, #0x0                    // #0
     95c:   d2800009    mov x9, #0x0                    // #0
     960:   d280000a    mov x10, #0x0                       // #0
     964:   d280000b    mov x11, #0x0                       // #0
     968:   d280000c    mov x12, #0x0                       // #0
     96c:   d280000d    mov x13, #0x0                       // #0
     970:   d280000e    mov x14, #0x0                       // #0
     974:   d280000f    mov x15, #0x0                       // #0
     978:   d2800010    mov x16, #0x0                       // #0
     97c:   d2800011    mov x17, #0x0                       // #0
     980:   d2800012    mov x18, #0x0                       // #0
     984:   d2800013    mov x19, #0x0                       // #0
     988:   d2800014    mov x20, #0x0                       // #0
     98c:   d2800015    mov x21, #0x0                       // #0
     990:   d2800016    mov x22, #0x0                       // #0
     994:   d2800017    mov x23, #0x0                       // #0
     998:   d2800018    mov x24, #0x0                       // #0
     99c:   d2800019    mov x25, #0x0                       // #0
     9a0:   d280001a    mov x26, #0x0                       // #0
     9a4:   d280001b    mov x27, #0x0                       // #0
     9a8:   d280001c    mov x28, #0x0                       // #0
     9ac:   d280001d    mov x29, #0x0                       // #0
     9b0:   d280001e    mov x30, #0x0                       // #0

节的反汇编。文本：
0000000000000000 :
0:1400024e b 938
...
200:14000061 b 384
...
280:14000082B488
...
300:140000a1 b 584
...
380:14000099 b 5e4
0000000000000938 :
938:d2800000 mov x0，#0x0/#0
93c:d2800001 mov x1，#0x0/#0
940:d2800002 mov x2，#0x0/#0
944:d2800003 mov x3，#0x0/#0
948:d2800004 mov x4，#0x0/#0
94c:D280005MOVx5，#0x0/#0
950:D280006 mov x6，#0x0/#0
954:d2800007 mov x7，#0x0/#0
958:d2800008 mov x8，#0x0/#0
95c:d2800009 mov x9，#0x0/#0
960:D28000A mov x10，#0x0/#0
964:d280000b mov x11，#0x0/#0
968:D28000C mov x12，#0x0/#0
96c:d280000d mov x13，#0x0/#0
970:d280000e mov x14，#0x0/#0
974:d280000f mov x15，#0x0/#0
978:d2800010 mov x16，#0x0/#0
97c:d2800011 mov x17，#0x0/#0
980:d2800012 mov x18，#0x0/#0
984:d2800013 mov x19，#0x0/#0
988:d2800014 mov x20，#0x0/#0
98c:d2800015 mov x21，#0x0/#0
990:d2800016 mov x22，#0x0/#0
994:d2800017 mov x23，#0x0/#0
998:d2800018 mov x24，#0x0/#0
99c:d2800019 mov x25，#0x0/#0
9a0:d280001a mov x26，#0x0/#0
9a4:d280001b mov x27，#0x0/#0
9a8:d280001c mov x28，#0x0/#0
9ac:d280001d mov x29，#0x0/#0
9b0:d280001e mov x30，#0x0/#0

当然，这确实使得优雅地返回u-boot变得不可能，即使这是一种很好的方法，如果您不必返回被调用方

c） u-boot执行的程序应该返回到调用代码，但演示程序的启动代码实际上进入了一个无休止的循环，这通常很好，但在您的用例中不是这样：

00000000000014c0 <_exit>:
    14c0:   14000000    b   14c0 <_exit>

00000000000014c0:
14c0:14000000B 14c0

解决当前行为需要修改Vitis提供的启动代码，或使用您自己的修改版本，以便：

• u-boot使用的寄存器将被保存/恢复
• 程序将返回，而不是进入无休止的循环

当然，您应该如上所述修改

go

命令的行为，这样程序就不会在

EL1

上执行：这对于安全和生产系统来说是完美的，但对于学习来说确实是有害的。我个人在学习

Armv8-a

体系结构时，正在使用运行于

EL3

的u-boot

---

这将需要更多的工作/测试，可能值得，也可能不值得，这取决于您计划做什么。

我删除了我的原始答案，因为我忽略了您能够执行

add.bin

，只有第二次尝试失败，因为程序在切换到

EL1

后返回。我最终能够下载。使用Vitis，并分解hello_world程序。第二个版本应该正确地回答您的原始问题。更具体地说，它确实解释了为什么您的程序永远不会返回u-boot命令提示符。@Prasanna Kotrappa这是否回答了您最初的问题，还是需要改进？谢谢

#include <stdint.h>
int main(int argc, char** argv) {
    register uint64_t __regCurrentEL;
    __asm volatile ("mrs %0, CurrentEL" : "=r" (__regCurrentEL));
    return __regCurrentEL >> 2;
}

CROSS_COMPILE=/opt/arm/10/gcc-arm-10.2-2020.11-x86_64-aarch64-none-elf/bin/aarch64-none-elf-
${CROSS_COMPILE}gcc -O0 -nostdlib -nostartfiles -e main -Wl,-Ttext=0x0000000042000000 -o el.elf el.c
${CROSS_COMPILE}objdump -D el.elf > el.lst
${CROSS_COMPILE}objcopy  el.elf -O srec el.srec

=> loads
## Ready for S-Record download ...

## First Load Addr = 0x42000000
## Last  Load Addr = 0x42000023
## Total Size      = 0x00000024 = 36 Bytes
## Start Addr      = 0x42000000    => go 0x42000000

## Starting application at 0x42000000 ...
## Application terminated, rc = 0x2
=>

fatload mmc 1 0x42000000 el.bin

int main(int argc, char** argv) {
    int rc = 0;

    for (int i = 1; i < argc; i++) {
        rc += *argv[i] - '0';
    }

    return rc;
}

CROSS_COMPILE=/opt/arm/10/gcc-arm-10.2-2020.11-x86_64-aarch64-none-elf/bin/aarch64-none-elf-
${CROSS_COMPILE}gcc -O0 -nostdlib -nostartfiles -e main -Wl,-Ttext=0x0000000042000000 -o add.elf add.c
${CROSS_COMPILE}objdump -D add.elf > adl.lst
${CROSS_COMPILE}objcopy  add.elf -O srec add.srec

loads
## Ready for S-Record download ...

## First Load Addr = 0x42000000
## Last  Load Addr = 0x4200006B
## Total Size      = 0x0000006C = 108 Bytes
## Start Addr      = 0x42000000
=> go 0x42000000
## Starting application at 0x42000000 ...
## Application terminated, rc = 0x0
=> go 0x42000000  1
## Starting application at 0x42000000 ...
## Application terminated, rc = 0x1
=> go 0x42000000  1 3 5
## Starting application at 0x42000000 ...
## Application terminated, rc = 0x9
=>

fatload mmc 1 0x6000000 add.bin
108 bytes read in 9 ms (11.7 KiB/s)
$ go 0x6000000
## Starting application at 0x06000000...
## Application terminated, rc = 0x0

go 0x6000000 1
## Starting application at 0x06000000 ...
FAIL: current EL is not above EL1
## Application terminated, rc = 0x16

unsigned long do_go_exec(ulong (*entry)(int, char * const []), int argc,
             char *const argv[])
{
    int ret = 0;

    if (current_el() > 1) {
        smp_kick_all_cpus();
        dcache_disable();
        armv8_switch_to_el1(0x0, 0, 0, 0, (unsigned long)entry,
                    ES_TO_AARCH64);
    } else {
        printf("FAIL: current EL is not above EL1\n");
        ret = EINVAL;
    }
    return ret;
}

unsigned long do_go_exec(ulong (*entry)(int, char * const []), int argc,
             char *const argv[])
{
    int ret = 0;

    if (current_el() > 1) {
        smp_kick_all_cpus();
        dcache_disable();
        ret = entry(argc, argv);
    } else {
        printf("FAIL: current EL is not above or equal to EL1\n");
        ret = EINVAL;
    }
    return ret;
}

Disassembly of section .text:

0000000000000000 <_vector_table>:
       0:   1400024e    b   938 <_boot>
    ...
     200:   14000061    b   384 <SynchronousInterruptHandler>
    ...
     280:   14000082    b   488 <IRQInterruptHandler>
    ...
     300:   140000a1    b   584 <FIQInterruptHandler>
    ...
     380:   14000099    b   5e4 <SErrorInterruptHandler>


0000000000000938 <_boot>:
     938:   d2800000    mov x0, #0x0                    // #0
     93c:   d2800001    mov x1, #0x0                    // #0
     940:   d2800002    mov x2, #0x0                    // #0
     944:   d2800003    mov x3, #0x0                    // #0
     948:   d2800004    mov x4, #0x0                    // #0
     94c:   d2800005    mov x5, #0x0                    // #0
     950:   d2800006    mov x6, #0x0                    // #0
     954:   d2800007    mov x7, #0x0                    // #0
     958:   d2800008    mov x8, #0x0                    // #0
     95c:   d2800009    mov x9, #0x0                    // #0
     960:   d280000a    mov x10, #0x0                       // #0
     964:   d280000b    mov x11, #0x0                       // #0
     968:   d280000c    mov x12, #0x0                       // #0
     96c:   d280000d    mov x13, #0x0                       // #0
     970:   d280000e    mov x14, #0x0                       // #0
     974:   d280000f    mov x15, #0x0                       // #0
     978:   d2800010    mov x16, #0x0                       // #0
     97c:   d2800011    mov x17, #0x0                       // #0
     980:   d2800012    mov x18, #0x0                       // #0
     984:   d2800013    mov x19, #0x0                       // #0
     988:   d2800014    mov x20, #0x0                       // #0
     98c:   d2800015    mov x21, #0x0                       // #0
     990:   d2800016    mov x22, #0x0                       // #0
     994:   d2800017    mov x23, #0x0                       // #0
     998:   d2800018    mov x24, #0x0                       // #0
     99c:   d2800019    mov x25, #0x0                       // #0
     9a0:   d280001a    mov x26, #0x0                       // #0
     9a4:   d280001b    mov x27, #0x0                       // #0
     9a8:   d280001c    mov x28, #0x0                       // #0
     9ac:   d280001d    mov x29, #0x0                       // #0
     9b0:   d280001e    mov x30, #0x0                       // #0

00000000000014c0 <_exit>:
    14c0:   14000000    b   14c0 <_exit>