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[Q] Are bootloaders backwards compatible

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creepyncrawly
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Originally Posted by jpasher View Post
I grabbed the file for UCMD8 (4.1.2) and I'll play around with that. I tried to grab UCLL6 (4.0.4) too, but the links point to the defunct hotfile site. Do you have updated links for that file (or is it exactly the same as what I can download at sammobile.com)? The full stock binaries (.tar.md5) go in the ODIN PDA slot, right?
I haven't finished uploading files to dev-host yet. But I'll be sure to upload that one today. I don't think you can get the file from sammobile either. They also used hotfile, and have not re-uploaded their complete library yet.

Yes, put the tar.md5 in the pda slot.

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Also, for those that may be interested, I made a copy of the bootloader from my stock UCKH7 (partition /dev/block/mmcblk0p2) and looked for strings related to the ODIN download mode, and I was able to find all of the strings that appear when in download (e.g. "ODIN MODE", "PRODUCT NAME", "ERASING DOWNLOAD INFORMATION", etc), so it's safe to say that ODIN download mode is part of the bootloader. All the more reason to just leave the bootloader alone if possible.
So you dd'd the contents of 0p2 and looked at that? What tool did you use to look for strings? And do you know if that is boot.bin or sbl.bin? I think it must be boot.bin.

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I also noticed that the two bootloader partitions (mmcblk0p2 and mmcblk0p3) are almost identical except for the text string SNBL in the mmcblk0p2 partition. I wonder why the two partitions...
Is it possible that there is built in redundancy? If one partition is bad, the second one can be used?
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creepyncrawly
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I have uploaded UCLL6 Odin Flashable tar.md5 to dev-host and posted it in the Download Repository.

By the way, I forgot so didn't mention it earlier in the discussion, but both UCLE5 and UCLL6 contain boot bin, but do not contain either sbl.bin or param.lfs. Evidently, the secondary boot loader and param files were not updated in the upgrade from Gingerbread to ICS.
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jpasher
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Thanks for the files. One more question about them. If I simply remove the boot.bin and sbl.bin from the tar file and flash, that's the same as the "no bootloader" flash images, right? Maybe param.lfs too? I'm just thinking of ways to make things safer while I'm doing my initial testing (and bleggy seems to be running newer ROMs off the original GB bootloader).

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Originally Posted by creepyncrawly View Post
So you dd'd the contents of 0p2 and looked at that? What tool did you use to look for strings? And do you know if that is boot.bin or sbl.bin? I think it must be boot.bin.
It was definitely the SBL, because it's a 1.25MB image instead of the 128K first stage bootloader. I found this thread about the Captivate (another extra phone I have) that says it works the same way (and does a good job explaining the boot process). I haven't figured out where the first stage bootloader (boot.bin) is stored, since it's not in a partition. I'll have to do some research on that.

In Linux, there's actually a command called strings that you can run on a file and it will extract all of the text strings it can find. A grep of that can find specific text. You could of course do the same thing by opening the file in a hex editor.

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Is it possible that there is built in redundancy? If one partition is bad, the second one can be used?
That was my thought, but I'm not brave enough to experiment to see if that's true.
 
bleggy
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whats the point, anyway? having consistent bootloader and rom doesnt seem to matter and plenty of i777 owners are running kitkat which there is no available bootloader to download and flash.

Is this an OCD thing? I get flashing the various modems for signal improvement, but I've never had a problem booting any rom with my old GB or ICS bootloader.

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creepyncrawly
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(Last edited by creepyncrawly; 5th January 2014 at 01:33 AM.)
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One more question... If I simply remove the boot.bin and sbl.bin from the tar file and flash, that's the same as the "no bootloader" flash images, right? Maybe param.lfs too?
Yes, that would be true. As long as you are using Linux to tar the remaining files, they should flash fine. I guess you can add the md5 if you want also.

The UCLE5 and UCLL6 one-click downloaders that I posted have the boot.bin removed. The UCLE5 and UCLL6 stock plus root also have the boot.bin removed. No one has ever said anything about any problems resulting.

My assumption is that it's ok to keep gingerbread boot loaders, or to flash the ICS boot loader, or to flash the JB boot loaders, and you would never be able to tell the difference. On the other hand, there must be a reason that Samsung puts them into the kies download. I just have no knowledge and no speculation on how they differ, or whether it is important to have matching boot loaders.

Edit: Oh, and boot.bin probably goes into 0p0 partition, just a guess. But it gets flashed in the pda slot just like sbl and param, so it must go into a partition.

Edit: A forum friend found this thread for us.

Edit: I just found Adam Outler's online pit file analyzer and ran the pit file from the Download Repository through it. Partition information for the AT&T SGS2 attached.
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File Type: txt SGS2 partition info.txt - [Click for QR Code] (6.8 KB, 3 views)
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jpasher
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Quote:
Originally Posted by bleggy View Post
whats the point, anyway? having consistent bootloader and rom doesnt seem to matter and plenty of i777 owners are running kitkat which there is no available bootloader to download and flash.
I have no reason to make the bootloader match the ROM. I'm just making sure I understand how everything works together to avoid doing something that may potentially brick my phone. I flashed the no bootloader version of stock UCMD8 today and everything seems to be working fine. As long as things work, I don't really care which bootloader I have.

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Originally Posted by creepyncrawly View Post
Edit: Oh, and boot.bin probably goes into 0p0 partition, just a guess. But it gets flashed in the pda slot just like sbl and param, so it must go into a partition.
There's not a "zero" partition. My only guess is that it's embedded somewhere else. Not sure at this point.

I found that post the other day with the S2 partition layout (that's what I was using for my tests). The PIT file analysis gives a little more info, although it says boot.bin partition is 0 bytes. That's what confuses me a bit. But in the end, not really a big deal. More of a curiosity than anything else.
 
yosmokinman
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When this forum was active "Don't mess with bootloaders" was common knowledge. Unless you absolutely have to. You can hard brick this thing if there's a problem while flashing it.

Don't mess with any of the files you mentioned. As far as I know it's unnecessary. I'm running Renders CM11 build with no problems with the original GB bootloader. Never had a problem with ICS or JB roms either.
 
jpasher
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Yea, my main purpose for starting the thread was to make sure I wouldn't break anything beyond repair by having mismatched bootloaders. It makes perfect sense why corrupting the bootloader would hose things (just like if you corrupted the MBR of your hard drive and had to boot off of alternative media to repair it, except for the fact that the phone does not have the ability to boot alternative media). My ASUS Transformer TF300T is nice in that aspect as the Nvidia chipset allows booting into APX mode which is an extremely low level boot mode that allows repair of almost anything. It should would be nice if the additional bootloader slot on the S2 could be used as a fallback with a way to choose which bootloader to run.

I'm the kind of person that likes to know more about the innards of how something works instead of looking at it as a black box. When I'm "flashing the kernel", I like to know exactly what it is I'm changing so I can understand the repercussions, especially if something goes wrong.

So the net result after this conversation is that I'm a lot more confident about flashing android devices (as long as I stay clear of messing with the bootloader whenever possible). I have CM11 running now too (stock CM kernel) while still on the GB bootloader.

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