Dear Wolfgang
Am Samstag, den 12.08.2017, 20:39 +0200 schrieb Wolfgang Denk:
Dear Max,
In message 20170812090346.7887-3-max.krummenacher@toradex.com you wrote:
If compiling for thumb the U-Boot 'go' command can not jump to the entry point, as the jump will be done in the assumption that the code jumped to is using the arm instruction set.
So add add a simple forwarder in arm instruction set which then jumps to the 'real' entry.
This description makes no sense to me. Whatever you do, the address where the image starts executuin is what is called the entry point. Whether this is needs special code to swutch to thumb mode or not does not make any difference. Whichever address you use with the "go" command is the "entry point".
Also, can the mode switching not be done inside the body of the regular hello_world() function? This would be much better as it wuld allow to always use the same method to determine the entry point address (line running "nm" on the binary and grepping for the name "hello_world"). With your code, you would have to fix all documentation and explain that the entry pooint name is suddenly domething totally different (and an unexpected, unusal name like "dummy2" as well) for thumb images.
This again stems from my assumption that one has to write the standalone application in a way that the entry point is actually linked to the beginning of the binary.
One cannot put the mode switching from thumb to arm instruction set inside the body of a C function, as the entry code prepended by the compiler would be in thumb and thus an exception would occur before the mode switching code gets executed.
Probably one can add a pragma conditionally so that the entry function gets compiled in arm instruction set. I investigate further and send a v2.
Max
Sorry, but this does not seem a good idea to me.
Naked-by: Wolfgang Denk wd@denx.de
Best regards,
Wolfgang Denk