On Tue, Aug 15, 2017 at 03:21:15PM +0200, Wolfgang Denk wrote:
Dear Tom,
In message 20170815113952.GE20467@bill-the-cat you wrote:
What CONFIG_STANDALONE_LOAD_ADDR is, is the location that we want hello_world, or other example stand alone applications loaded into memory at. CONFIG_LOADADDR is the safe default location to load things into memory at in order to run them. At least on ARM, where there's a good number of different default memory layouts, what arch/arm/config.mk does today is broken for the majority of platforms.
I agree up to here.
We should be providing at least a functional default value here, which we are not today. This in no way precludes a 'real' standalone application from linking and running at whatever it wants within a platforms memory map.
This is where things become fishy.
We should use clean terms.
OK.
Please keep in mind that even the term "load address" can mean two things: many people use this term (incorrectly) for the address where they load an image to on RAM, and unfortunately we even provide the "loadaddr" environment variable which carries this meaning.
We'll use this for now at least, for consistency.
Originally, the term refers to the address where the image payload gets uncompressed and loaded to when unpacking the image. For example, on Power architecture, a typical setup would look like:
Output of mkimage -l:
Image Name: Linux-4.4.8 Created: Fri Apr 22 09:06:09 2016 Image Type: PowerPC Linux Kernel Image (gzip compressed) Data Size: 2009139 Bytes = 1962.05 kB = 1.92 MB Load Address: 00000000 Entry Point: 00000000
We download the uImage file to - say - 0x400000 in RAM (so the environment variable "loadaddr" might be 0x400000), but when we run "bootm", U-Boot will uncompress and _load_ the Linux kernel to the _Load_Address_ stored in the image header, i. e. 0x00000000, and then it will transfer control to the _Entry_Point_Address_, also stored in the image header, here also 0x00000000.
So we have:
download address (address of image in RAM): 0x00400000 load address (start of unpacked kernel image): 0x00000000 entry point (start of executable code): 0x00000000
The term "load address" has always been meant to mean the address where the kernel gets _loaded_to_ by the bootm command. I know that there has always been confusion of these terms, and I must have explained this at least a hundred times here before.
This is all true. But it's also unrelated to what CONFIG_STANDALONE_LOAD_ADDR is used for. So...
I would really appreciate if you helped to avoid mixing terms of different meaning. If you have an idea how to avoid this it would be more than welcome - unfortunately the (mis)use of the loadaddr environment variable is so widespread that I feat there is no easy way out.
I think the first problem is that we need to rename CONFIG_STANDALONE_LOAD_ADDR to CONFIG_EXAMPLE_STANDALONE_ENTRY_POINT to be more precise about what it is doing and used for, all around. And then, I'm not sure. I had an idea, but I seem to have found that at least right this moment, hello_world.bin doesn't function for me and I would swear I had unit tested be1b8679ce42 but it is not working for me either. But I'm going to put this down for the evening at least...