Re: Possible error in dtrace

[Maxime Villard <max%m00nbsd.net@localhost>]

Le 25/07/2018 à 15:54, Siddharth Muralee a écrit :
> Hello,
>        While going through sys/arch/amd64/pmap.h, I came across KERN_BASE[1] and confused it for KERNBASE[2]. Looking deeper into the same I think someone made the same mistake in dtrace_isa.c{3](I might be wrong).
>      I compared how the same variable was used in amd64[4] and i386[5]. There seems to be a mismatch. I computed the values for KERN_BASE and KERNBASE for amd64 and
>
>   * KERN_BASE = 0x800000000000
>   * KERNBASE = 0xffffffff80000000
>
> I think this may be an error. However, the names are definitely a bit confusing and there is no documentation to suggest what they are for.

They are not the same. KERNBASE is the base where .text etc are located.
KERN_BASE is where the kernel map begins (VM_MIN_KERNEL_ADDRESS).

In fact, KERN_BASE is incorrect, there should be a VA_SIGN_NEG() around the
multiplication. I've always known this, but I don't know if it's really
harmful, so by default I've never fixed it.