Re: Capabilities, Anybody?

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Sujet : Re: Capabilities, Anybody?
De : already5chosen (at) *nospam* yahoo.com (Michael S)
Groupes : comp.arch
Date : 11. Mar 2024, 15:13:48
Autres entêtes
Organisation : A noiseless patient Spider
Message-ID : <20240311161348.00005123@yahoo.com>
References : 1 2 3 4 5 6 7 8 9 10 11 12 13
User-Agent : Claws Mail 3.19.1 (GTK+ 2.24.33; x86_64-w64-mingw32)
On Mon, 11 Mar 2024 16:10:09 +0200
Michael S <already5chosen@yahoo.com> wrote:

On 11 Mar 2024 11:10:15 +0000 (GMT)
Theo Markettos <theom+news@chiark.greenend.org.uk> wrote:
 
MitchAlsup1 <mitchalsup@aol.com> wrote: 
Theo Markettos wrote:   
The bounds have a certain representation limits, because they're
packing 192+ bits of information into a 128 bit space.  This
boils down to an alignment granularity: eg if you allocate a
(1MiB+1) byte buffer the bounds might be 1MiB+64 (or whatever, I
can't remember what the rounding is at this size).  malloc()
should ensure it doesn't hand out that memory to somebody else;
allocators typically do this anyway since they use slab
allocators which round up the allocation to a certain number of
slabs.   
 
So how to you "encode" a petaByte array ?? of megaByte structs in
a capability ??   
 
You create a capability with petabyte-scale bounds.  The precision
of the bounds may be limited, which means that you can't ram
something else right up against the end or beginning of the array
if they aren't sufficiently aligned.  This is in practice not a
problem: slab allocators will round up your address before they
allocate the next thing, and most OSes won't populate the rounded
up space with pages anyway.
 
When you take a pointer to an array element, then it has megabyte
scale bounds and they can be represented with more precision.  If
your struct elements are of an arbitrary size and packed together at
the byte level then you either have to live with the bounds giving
rights to slightly more than a single struct element, or you decide
that is unacceptable and pad the struct size up to the next
representable size (just like regular non-packed structs enforce
certain alignment), and pay a small memory overhead for that
(<0.25%).  That's a security decision you can make one way or
another.
 
Theo 
 
Your time stamp (most likely +0000 part) confuses my Claws
Mail newsreader. I wonder if others see similar problem.
 

After further examination, it's unlikely that +0000 is a confusing
part. More likely my newsreader does not understand (GMT)


Date Sujet#  Auteur
9 Mar 24 * Capabilities, Anybody?78Lawrence D'Oliveiro
9 Mar 24 +* Re: Capabilities, Anybody?74mitchalsup@aol.com (MitchAlsup1)
9 Mar 24 i+- Re: Capabilities, Anybody?1BGB
9 Mar 24 i+* Re: Capabilities, Anybody?71BGB
9 Mar 24 ii+* Re: Capabilities, Anybody?61Robert Finch
9 Mar 24 iii+- Re: Capabilities, Anybody?1Lawrence D'Oliveiro
10 Mar 24 iii`* Re: Capabilities, Anybody?59BGB
10 Mar 24 iii +- Re: Capabilities, Anybody?1Chris M. Thomasson
10 Mar 24 iii `* Re: Capabilities, Anybody?57Theo Markettos
10 Mar 24 iii  +* Re: Capabilities, Anybody?4John Dallman
11 Mar 24 iii  i`* Re: Capabilities, Anybody?3Theo
17 Mar 24 iii  i `* Re: Capabilities, Anybody?2John Dallman
18 Mar 24 iii  i  `- Re: Capabilities, Anybody?1Robert Finch
10 Mar 24 iii  +* Re: Capabilities, Anybody?19MitchAlsup1
11 Mar 24 iii  i`* Re: Capabilities, Anybody?18Theo Markettos
11 Mar 24 iii  i +* Re: Capabilities, Anybody?10MitchAlsup1
11 Mar 24 iii  i i`* Re: Capabilities, Anybody?9Theo Markettos
11 Mar 24 iii  i i +- Re: Capabilities, Anybody?1George Neuner
11 Mar 24 iii  i i `* Re: Capabilities, Anybody?7Michael S
11 Mar 24 iii  i i  +- Re: Capabilities, Anybody?1Michael S
11 Mar 24 iii  i i  `* Re: Capabilities, Anybody?5Michael S
11 Mar 24 iii  i i   `* Broken Date formats4Michael S
11 Mar 24 iii  i i    `* Re: Broken Date formats3Michael S
11 Mar 24 iii  i i     `* Re: Broken Date formats2Michael S
11 Mar 24 iii  i i      `- Re: Broken Date formats1Michael S
11 Mar 24 iii  i `* Re: Capabilities, Anybody?7Chris M. Thomasson
12 Mar 24 iii  i  `* Re: Capabilities, Anybody?6Chris M. Thomasson
13 Mar 24 iii  i   `* Re: Capabilities, Anybody?5BGB
14 Mar 24 iii  i    `* Re: Capabilities, Anybody?4Chris M. Thomasson
14 Mar 24 iii  i     `* Re: Capabilities, Anybody?3BGB
14 Mar 24 iii  i      `* Re: Capabilities, Anybody?2Chris M. Thomasson
16 Mar 24 iii  i       `- Re: Capabilities, Anybody?1BGB
10 Mar 24 iii  `* Re: Capabilities, Anybody?33BGB
11 Mar 24 iii   `* Re: Capabilities, Anybody?32Robert Finch
11 Mar 24 iii    `* Re: Capabilities, Anybody?31BGB
13 Mar 24 iii     `* Re: Capabilities, Anybody?30Robert Finch
13 Mar 24 iii      +* Re: Capabilities, Anybody?24MitchAlsup1
13 Mar 24 iii      i`* Re: Capabilities, Anybody?23Robert Finch
13 Mar 24 iii      i +* Re: Capabilities, Anybody?21MitchAlsup1
14 Mar 24 iii      i i`* Re: Capabilities, Anybody?20Robert Finch
14 Mar 24 iii      i i +- Re: Capabilities, Anybody?1Lawrence D'Oliveiro
14 Mar 24 iii      i i `* Re: Capabilities, Anybody?18MitchAlsup1
14 Mar 24 iii      i i  `* Re: Capabilities, Anybody?17Lawrence D'Oliveiro
14 Mar 24 iii      i i   +* Re: Capabilities, Anybody?10MitchAlsup1
14 Mar 24 iii      i i   i`* Re: Capabilities, Anybody?9Lawrence D'Oliveiro
15 Mar 24 iii      i i   i `* Re: Capabilities, Anybody?8MitchAlsup1
15 Mar 24 iii      i i   i  +* Re: Capabilities, Anybody?2Chris M. Thomasson
15 Mar 24 iii      i i   i  i`- Re: Capabilities, Anybody?1Chris M. Thomasson
15 Mar 24 iii      i i   i  `* Re: Capabilities, Anybody?5Lawrence D'Oliveiro
15 Mar 24 iii      i i   i   `* Re: Capabilities, Anybody?4Chris M. Thomasson
15 Mar 24 iii      i i   i    `* Re: Capabilities, Anybody?3Lawrence D'Oliveiro
15 Mar 24 iii      i i   i     `* Re: Capabilities, Anybody?2Lawrence D'Oliveiro
15 Mar 24 iii      i i   i      `- Re: Capabilities, Anybody?1Chris M. Thomasson
14 Mar 24 iii      i i   +* Re: Capabilities, Anybody?5Lawrence D'Oliveiro
15 Mar 24 iii      i i   i`* Re: Capabilities, Anybody?4MitchAlsup1
15 Mar 24 iii      i i   i +- Re: Capabilities, Anybody?1Lawrence D'Oliveiro
18 Mar 24 iii      i i   i +- Re: Capabilities, Anybody?1Paul A. Clayton
18 Mar 24 iii      i i   i `- Re: Capabilities, Anybody?1MitchAlsup1
15 Mar 24 iii      i i   `- Re: Capabilities, Anybody?1MitchAlsup1
14 Mar 24 iii      i `- Re: Capabilities, Anybody?1Theo Markettos
13 Mar 24 iii      `* Re: Capabilities, Anybody?5BGB
14 Mar 24 iii       `* Re: Capabilities, Anybody?4Robert Finch
14 Mar 24 iii        `* Re: Capabilities, Anybody?3BGB
14 Mar 24 iii         +- Re: Capabilities, Anybody?1Lawrence D'Oliveiro
15 Mar 24 iii         `- Re: Capabilities, Anybody?1MitchAlsup1
10 Mar 24 ii`* Re: Capabilities, Anybody?9Theo Markettos
11 Mar 24 ii `* Re: Capabilities, Anybody?8BGB
11 Mar 24 ii  +* Re: Capabilities, Anybody?2Robert Finch
12 Mar 24 ii  i`- Re: Capabilities, Anybody?1BGB
12 Mar 24 ii  +* Re: Capabilities, Anybody?2BGB
12 Mar 24 ii  i`- Re: Capabilities, Anybody?1MitchAlsup1
14 Mar 24 ii  `* Re: Capabilities, Anybody?3Theo Markettos
14 Mar 24 ii   +- Re: Capabilities, Anybody?1MitchAlsup1
14 Mar 24 ii   `- Re: Capabilities, Anybody?1BGB
9 Mar 24 i`- Re: Capabilities, Anybody?1Lawrence D'Oliveiro
9 Mar 24 `* Re: Capabilities, Anybody?3Robert Finch
9 Mar 24  `* Re: Capabilities, Anybody?2Lawrence D'Oliveiro
9 Mar 24   `- Re: Capabilities, Anybody?1Robert Finch

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