[TUHS] Introduction

Jose R. Valverde jrvalverde at cnb.csic.es
Wed Jun 25 20:25:05 AEST 2008


	BTW, I am thiking more clearly now and realize I initially confused 
the uap struct in lock() with u_uap, although what is actually assigned is
uap->linkname to u.u_dirp.

	When seeing the type definitions in param.h I also notice that it
defines caddr_t (the type of the u.u_dirp.l side of the saddr_t union) as

typedef char 		*caddr_t;	/* pointer to kernel things */

that leads me to consider that the &0x7F00FFFF may be an additional 
security check to ensure that the pointer falls within valid memory 
space, in which case it would match the memory map.

I notice that nsseg in mch.s may return %7F00 on some cases and is used
in machdep.c as stseg = nsseg(u_state->s_sp); so it seems the stack uses
segment 0x7F00. Then may be the & is shorthand to make sure the address
pointed by the ANDed pointer falls within the stack. It would probably
imply user programs have a maximum stack size of 65536 bytes as well.

That may explain why some pointers are ANDed and others not. I haven't
had a thorough look, but if the &0x7F00FFFF usage is consistent, then
that's is an explanation that may guide source reconstruction.

Does this look sensible?


	These opinions are mine and only mine. Hey man, I saw them first!

			    José R. Valverde

	De nada sirve la Inteligencia Artificial cuando falta la Natural
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