On Sun, May 19, 2019 at 04:46:44PM +0200, Ingo Schwarze wrote:
> Hi,
>
> Otto Moerbeek wrote on Sun, May 19, 2019 at 02:55:09PM +0200:
> > On Sun, May 19, 2019 at 08:50:20AM +0200, Jan Stary wrote:
>
> >> Does 'J' simply make the junk level two and
> >> does 'j' simply make the junk level zero?
>
> No, it does not.
>
> For example, if sysctl vm.malloc_conf contains j and MALLOC_OPTIONS
> contains J, or if any one source contains "jJ" or "jjJ", you end
> up with level 1: During the first malloc call in the program, the
> j first lowers the level from 1 to 0, then the J raises the level
> back to 1, but not to 2.
>
> >> The current "increase/decrease" wording in malloc(3)
> >> can suggest it has a memory. For example, setting
> >>
> >> vm.malloc_conf=J
> >>
> >> "increases" junk level to two;
> >> does setting
> >>
> >> vm.malloc_conf=C
> >>
> >> later retain a junk level of two,
> >> as there is no 'j' to "decrease" it,
> >> or is the junk level the defult of one now?
>
> Your question makes no sense whatsoever.
>
> First, the word "later" makes no sense. Malloc initialization is
> only done once during a run of any given program. So if the sysctl
> contains J during startup, that is what governs program behaviour.
> Changing the sysctl later no longer has any effect on the running
> program.
>
> Besides, while J and j manipulate mopts.def_malloc_junk, C sets
> mopts.chunk_canaries. One doesn't have anything to do with the
> other.
>
> > C is a combined flag, containing J amongst others.
>
> Neither the code nor the manual page appears to agree with that
> statement. Are you maybe thinking of S?
yes, I was thinking of S indeed.
>
> To provide another example, MALLOC_OPTIONS=jS results in junk level
> 1 because j lowers it from 1 to 0, then S raises it from 0 to 1.
> MALLOC_OPTIONS=jSS results in junk level 2, whereas MALLOC_OPTIONS=SSj
> results in junk level 1.
>
>
> The manual page already seems quite clear. Well, maybe we could
> add one sentence for even more clarity. Right now, some might think
> that earlier flags win.
>
> OK?
> Ingo
yes,
-Otto
>
>
> Index: malloc.3
> ===================================================================
> RCS file: /cvs/src/lib/libc/stdlib/malloc.3,v
> retrieving revision 1.124
> diff -u -r1.124 malloc.3
> --- malloc.3 13 May 2019 06:04:55 -0000 1.124
> +++ malloc.3 19 May 2019 14:39:30 -0000
> @@ -270,6 +270,8 @@
> in the program.
> Each is scanned for the flags documented below.
> Unless otherwise noted uppercase means on, lowercase means off.
> +During initialization, flags occurring later modify the behaviour
> +that was requested by flags processed earlier.
> .Bl -tag -width indent
> .It Cm C
> .Dq Canaries .
