enorm wrote:
Hi, Some "naive" questions about u-boot for MPC85xx, the definition of some macro in ppc_asm.tmpl. Can anyone there explain them to me please?
- In GET_GOT(x) what does " lwz r0,0b-1b(r14) ;" do? what does
"0b-1b" stands for, or the meaning of the syntax? why move the content of the memory pointing by LR?
#define GET_GOT \
bl 1f ; \ .text 2 ; \0: .long .LCTOC1-1f ; \ .text ; \ 1: mflr r14 ; \ lwz r0,0b-1b(r14) ; \ add r14,r0,r14 ;
- In START_GOT, any special meaning for the value 32768?
.LCTOC1=.+32768
- Syntax for GOT_ENTRY(NAME) and GOT(NAME), like . - .LCTOC1 (line
- and .text 2 (line 50)
could not find then in the GNU douments (ld, as, gcc, glibc etc).
Thanks for the help!!
1) 0b and 1b are references to label "0" and "1" in the backwards direction (this is a way to generate and reference "anonymous" labels.
The mflr r14 is getting the return address, which is the start of this snippet of code - the "bl 1f" does a "subroutine call" to label 1 in the forward direction, resulting in the link register containing a pointer to the label 0 IIRC. The lwz is picking up a relative pointer to .LCTOC1 and doing some compensation so that the "add" instruction results in the correct absolute pointer to the GOT table, regardless of where the code is actually being executed (speculating towards the end, there).
gvb