[U-Boot] [PATCH 2/2] hello_world.c: fix entry point in case of arm thumb binary

[Wolfgang Denk]

Dear Max,

In message <1502573515.17070.20.camel at gmail.com> you wrote:
> 
> 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.

No, this stems from your confusion of load address and entry point
address.  Of course it is possib;e that the entry point is at the
very beginning of the binary.  In that case you must load the image
such into memory, that the start addresss of the binary is the same
as the entry point address.

But the load address is not the start of the binary in memory - it
is the start address of the _image_.   Almost always the bianry will
be just a payload within the image - in the most simple cases of the
lecagy uImage files the binary payload will be preceeded by a 64
byte image header.  So when your load addess is set to 0x100000,
the binary will NOT start at this address, but at an offset of 64
bytes.  So the entry poin can NEVER be the same as the load address,
as this is outside of the image payload.

> 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.

If this cannot be a regular C funtion, we should still be able to
provide some trampoline code using the same name.  My main goal is
to avoid confugion to the user who expects that he can look up the
entry point address in the nm ouutput under the well-known name.

> 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.

Thanks.

Best regards,

Wolfgang Denk

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