MPC8xx u-boot amcro definition

May 18, 2006 3 Replies

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hfei 20 years ago

Hi,

We are just moving to the linux and gnu world from other RTOS. First thing we try to port our own bootloader to U-boot for our MPC8xx board.

Some "naive" questions about u-boot for MPC8xx, the definition of some macro in ppc_asm.tmpl. Can anyone there explain them to me please?

1) 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 ;

2) In START_GOT, any special meaning for the value 32768? >> .LCTOC1=.+32768
3) Syntax for GOT_ENTRY(NAME) and GOT(NAME), like .L_ ## (NAME) ... could not find then in the GNU douments (ld, as, gcc, glibc etc).

Thanks for the helps!!

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Michael Schnell 20 years ago

I'm not fluent in 8xx ASM, but I _think_ 0b-1b just means -1 as an unsigned value, thus a value of the appropriate size with all bits set (supposing the 8xx uses normal integer representation. I do think

-1(r14) should do the same.

No idea.

## is as preprocessor directive that joining two strings. So if NAME is set to xyz , L_ ## (NAME) will be the string L_xyz.

-Michael

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Tauno Voipio 20 years ago

The expressions 0b and 1b refer to the local labels

0: and 1: back. The expression is negative of the distance between the labels 0: and 1:.

For details, see the GNU as manual, local labels.

Tauno Voipio tauno voipio (at) iki fi

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Michael Schnell 20 years ago

Right you are !

Silly me :( .

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