[U-Boot] Can not access global variable in uboot command function?
Jerry Van Baren
gvb.uboot at gmail.com
Mon Oct 12 03:28:24 CEST 2009
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
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