[U-Boot-Users] another question of relocate_code

[YanMin Qiao <sepherosa@sjtu.edu.cn>]

Wolfgang Denk wrote:

>In message <3E16E5AE.4090002@sjtu.edu.cn> you wrote:
>  
>
>>Hi all:
>>
>><u-boot>/cpu/mpc8xx/start.S
>>
>>....
>>relocate_code:
>>    mr    r1,  r3        /* Set new stack pointer        */
>>    mr    r9,  r4        /* Save copy of Global Data pointer    */
>>    mr    r10, r5        /* Save copy of Destination Address    */
>>....
>>    sub    r15, r10, r4
>>
>>    /* First our own GOT */
>>    add    r14, r14, r15
>>    /* the the one used by the C code */
>>    add    r30, r30, r15
>>              ^^^
>>....
>>
>>I have followed the code to the end of board_init_r().  I didn't figured 
>>out where r30 is used
>>as mentioned.
>>    
>>
>
>Which part of this section from the README didn't you understand?
>
>	... we are restricted  by  the 
>	relevant  (E)ABI  specifications for the current architecture, and by
>	GCC's implementation.
>	   
>	For PowerPC, the following registers have specific use:
>		R1:     stack pointer 
>		R2:     TOC pointer 
>		R3-R4:  parameter passing and return values
>		R5-R10: parameter passing 
>		R13:    small data area pointer 
>		R30:    GOT pointer 
>		R31:    frame pointer 
>	   
>		(U-Boot also uses R14 as internal GOT pointer.)
>
>If you want to know all the ugly details  I  recommend  to  read  the
>(E)ABI specifications and the relevant parts of the GCC source code.
>
>Best regards,
>
>Wolfgang Denk
>
>  
>
thanks for the mention of eabi  :)

Best regards