[U-Boot] Can not access global variable in uboot command function?

[Jerry Van Baren <gvb.uboot@gmail.com>]

Hi Wilbur,

wilbur.chan wrote:
> mips64 , xlr732
> 
> I've added a test command in uboot, say,
> U_BOOT_CMD(test_globa,...do_test_global)  ,which is  in cmd_command.c
> 
> And in cmd_command.c, there is also a global string array ,say ,char*
> p = "test";
> 
> In do_test_global,  I used pointer to access elements of array p like this:
> 
> char c = *(char*)p;
> 
> it seemd that , the code above caused uboot dead and print nothing ,I
> guess that,maybe there was a memory access violation.
> 
> Any suggestions on how could this happended? Thank you in advance

Just a guess, but I suspect your are getting bitten by the manual 
pointer relocation issue.

Your char *p is pointing into flash, but you are dereferencing the 
pointer after relocation to RAM, running out of RAM with a different 
memory map than power-on-reset (initialization has completed).  I 
suspect your flash image is no longer where it was on release of reset 
and thus dereferencing *p now tries to read an invalid memory location, 
causing your "hang."

If you really need the pointers, you need to manually relocate them. 
See ./include/asm-mips/global_data.h and the function
   void board_init_r (gd_t *id, ulong dest_addr)
in lib_mips/board.c.

The bottom line is that you probably need to add gd->reloc_off to your 
compiled-in pointers:
   *(p + gd->reloc_off)

[snip]

gvb