loader: fix endianness conversion

[royger]

Summary

r328536 broke symbol loading on amd64 at least (and probably other
arches). r328826 contained the problem to ppc only by adding
pre-processors guards.

Fix this properly by moving the endianness conversion to separate
helper functions, and make the conversion more robust by using sizeof
instead of having to manually code the size of each field.

Finally list the fields in each structure in a macro in order to avoid
code repetition.

Sponsored by: Citrix Systems R&D

Test Plan

Tested on AMD64 only, seems to WFM.

[wma]

Nice!

[emaste]

Existing indentation in this file is a mess, but there are a couple of new cases that don't match either of the two existing styles. I suggest tweaking this change to match the surrounding cases, and then someone (@imp or me, perhaps) should follow up with reformatting the portions that don't conform to style(9).

stand/common/load_elf.c

238

indentation - I think this one should be 2 tabs

510

indentation

587–588

indentation

[emaste]

This works in my QEMU test case and LGTM, modulo indentation nits.

[royger]

In D14267#299114, @emaste wrote:

Existing indentation in this file is a mess, but there are a couple of new cases that don't match either of the two existing styles. I suggest tweaking this change to match the surrounding cases, and then someone (@imp or me, perhaps) should follow up with reformatting the portions that don't conform to style(9).

Thanks! I've fixed those, but maybe we should think about re-formatting the whole file to match the coding standards. I think @imp has already done that for other loader related files.

stand/common/load_elf.c

154

I've constified ehdr here and below.