ee_boot.s questions for MPC5644a

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aladdin7938
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ee_boot.s questions for MPC5644a

Post by aladdin7938 » Mon Oct 03, 2016 3:57 am

Hi,Guys.I am pretty new to Erika OS. Lately, I'm reading source code of ee_boot.s, I notice there are some lines like "blt 1b" and "beq 2f". What are "1b" and "2f"? are those lable? or relative address offset? I search ee_boot.s over and over again and don't see any lable as "1b" or "2f".

My second question is also in this file "ee_boot.s", there are multiple instances of lable "1" , "2". Is this a special usage ? i read PowerPC assembly manual and find no similar usage.

Anyone can help me answer those questions?

Thanks a lot for your help!
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e.guidieri
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Re: ee_boot.s questions for MPC5644a

Post by e.guidieri » Mon Oct 03, 2016 10:17 am

Hi,

these are called numeric local labels, it's a GCC asm (gas) feature introduced in a bunch of other compilers (indeed those files are compiled with WindRiver DIAB verbatim and by NXP/Freescale METROWERKS[Codewarrior], after a code to code automatic translation procedure).

Basically the branches you pointed jump forward (f) or backwards (b), to the nearest numeric label of the same value.

Here a deeper explanation found in an ARM page (because ARM has the best documentation for embedded, period).

Chapter 4 Migrating ARM syntax assembly code to GNU syntax - 4.4 4.4 Numeric local labels

Errico

aladdin7938
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Joined: Mon Sep 26, 2016 5:50 am

Re: ee_boot.s questions for MPC5644a

Post by aladdin7938 » Mon Oct 03, 2016 8:21 pm

Thank you, Errico!

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