The CHERI capability model: Revisiting RISC in an age of risk (Light Blue Touchpaper)

the directory structure of a source code tree has no bearing on what is a separate architecture (e.g., the BSDs have kept i386/amd64 separate). if anything, it reflects on some wise engineerig design decisions of AMD that kept the two archs close enough that some linux devs managed to drive through the x86 'unification'. as for how successful the x86 merge is:

$ find linux-3.15.3/arch/x86/ | wc -l
1255
$ grep -rwn CONFIG_X86_32 linux-3.15.3/arch/x86/ | wc -l
414
$ grep -rwn CONFIG_X86_64 linux-3.15.3/arch/x86/ | wc -l
472
$ grep -rn 'def.*CONFIG_X86_32' linux-3.15.3/arch/x86/ | wc -l
341
$ grep -rn 'def.*CONFIG_X86_64' linux-3.15.3/arch/x86/ | wc -l
403
$ find linux-3.15.3/arch/x86/ -name '*_32.[ch]' | wc -l
59
$ find linux-3.15.3/arch/x86/ -name '*_64.[ch]' | wc -l
61
$ find linux-3.15.3/arch/x86/ -name '*_32.[chS]' | wc -l
81
$ find linux-3.15.3/arch/x86/ -name '*_64.[chS]' | wc -l
101

so after several years(!) of effort there're almost as many exceptions as 'unified' files, or in other words, it wasn't done because i386/amd64 are the same arch (which is, ironically, something you'd know yourself if you *actually* worked with these archs). so you tell me who's treating marketing BS as a gospel of truth.